Authors:Himadri Pandey; Jorge-Daniel Aguirre-Morales, Satender Kataria, Sebastien Fregonese, Vikram Passi, Mario Iannazzo, Thomas Zimmer, Eduard Alarcon, Max C. Lemme Abstract: We report on electronic transport in dual-gate, artificially stacked bilayer graphene field effect transistors (BiGFETs) fabricated from large-area chemical vapor deposited (CVD) graphene. The devices show enhanced tendency to current saturation, which leads to reduced minimum output conductance values. This results in improved intrinsic voltage gain of the devices when compared to monolayer graphene FETs. We employ a physics based compact model originally developed for Bernal stacked bilayer graphene FETs (BSBGFETs) to explore the observed phenomenon. The improvement in current saturation may be attributed to increased charge carrier density in the channel and thus reduced saturation velocity due to carrier-carrier scattering.Bilayer graphene has been suggested as an alternative for obtaining enhanced current saturation in graphene transistors. Large-area CVD grown graphene monolayers are used to prepare scalable artificially stacked bilayers (ASBLG) to study its electronic properties. Transistors based on ASBLG exhibit a reduction in minimum output conductance, resulting in an improved voltage gain compared to monolayer graphene transistors. Plausible reasons behind the present observation are discussed. PubDate: 2017-09-20T02:56:01.367528-05: DOI: 10.1002/andp.201700106

Authors:Bernhard Stanje; Daniel Rettenwander, Stefan Breuer, Marlena Uitz, Stefan Berendts, Martin Lerch, Reinhard Uecker, Günther Redhammer, Ilie Hanzu, Martin Wilkening Abstract: The development of all-solid-state electrochemical energy storage systems, such as lithium-ion batteries with solid electrolytes, requires stable, electronically insulating compounds with exceptionally high ionic conductivities. Considering ceramic oxides, garnet-type Li7La3Zr2O12 and derivatives, see Zr-exchanged Li6La3ZrTaO12 (LLZTO), have attracted great attention due to its high Li+ ionic conductivity of 10−3 S cm−1 at ambient temperature. Despite numerous studies focussing on conductivities of powder samples, only few use time-domain NMR methods to probe Li ion diffusion parameters in single crystals. Here we report on temperature-variable NMR relaxometry measurements using both laboratory and spin-lock techniques to probe Li jump rates covering a dynamic time window spanning several decades. Both techniques revealed a consistent picture of correlated Li ion jump diffusion in the single crystal; the data perfectly mirror a modified BPP-type relaxation response being based on a Lorentzian-shaped relaxation function. The rates measured could be parameterized with a single set of diffusion parameters. Results from NMR are completely in line with ion transport parameters derived from conductivity spectroscopy.The Li ions in single crystals of Li6La3ZrTaO12 are exposed to fast very fast exchange processes. The reason behind these fast hopping processes, which have been revealed by NMR spin-lattice relaxometry, is an enhanced pre-factor of the underlying Arrhenius relation that boosts ion dynamics above room temperature. The pre-factor is, besides other factors, influenced by entropic contributions. PubDate: 2017-09-13T01:08:55.999298-05: DOI: 10.1002/andp.201700140

Authors:Carlos Ramírez Abstract: Calculation of the scattering matrix (S-matrix) of a system allows direct determination of its transport properties. Within the scattering theory, S-matrices relate amplitudes of incoming and outgoing waves in semi-infinite leads attached to a scattering region. Recently, an assembly method to calculate S-matrices of arbitrary tight-binding systems connected to atomic chains has been proposed, were the S-matrices of subsystems are used to obtain S-matrix of the total system. In this paper, a new efficient method to obtain S-matrices of general periodic leads is established, which can be used in the mentioned assembly method, allowing to address coherent quantum transport of arbitrary multiterminal systems with complex geometries trough Landauer-Büttiker formalism. In addition, a new method to determine extended-state band structures of general infinite periodic wires is presented, which exploits properties of the S-matrix. Finally, these methods are used to obtain band structure of graphene arm-chair and zig-zag nanoribbons and transmission functions in three terminal Z-shaped graphene nanoribbon structures.In this work, a new method to determine the S-matrix of semi-infinite periodic tight-binding systems is described. This method is compatible with an assembly process that allow determination of transport properties of complex systems by using simpler elements. Transmission functions of Z-shape graphene systems with arm-chair and zig-zag leads, as shown in figure, are determined as instances of application. PubDate: 2017-09-13T01:07:39.593601-05: DOI: 10.1002/andp.201700170

Authors:Maxim F. Gelin; Raffaele Borrelli Abstract: We develop a wave-function-based method for the simulation of quantum dynamics of systems with many degrees of freedom at finite temperature. The method is inspired by the ideas of Thermo Field Dynamics (TFD). As TFD, our method is based on the doubling of the system's degrees of freedom and thermal Bogoliubov transformation. As distinct from TFD, our method implements the doubling of thermalized degrees of freedom only, and relies upon the explicitly constructed generalized thermal Bogoliubov transformation, which is not restricted to fermionic and bosonic degrees of freedom. This renders the present approach computationally efficient and applicable to a large variety of systems.The authors develop a wave-function-based method for the simulation of quantum dynamics of systems with many degrees of freedom at finite temperature.The method is inspired by the ideas of Thermo Field Dynamics. It implements the doubling of thermalized degrees of freedom and relies upon the explicitly constructed thermal Bogoliubov transformation, which is not restricted to fermionic and bosonic degrees of freedom. PubDate: 2017-09-06T01:51:03.322141-05: DOI: 10.1002/andp.201700200

Authors:Evgueni Talantsev; Wayne P. Crump, Jeffery L. Tallon Abstract: Key questions for any superconductor include: what is its maximum dissipation-free electrical current (its ‘critical current') and can this be used to extract fundamental thermodynamic parameters' Present models focus on depinning of magnetic vortices and implicate materials engineering to maximise pinning performance. But recently we showed that the self-field critical current for thin films is a universal property, independent of microstructure, controlled only by the penetration depth. Here, using an extended BCS-like model, we calculate the penetration depth from the temperature dependence of the superconducting energy gap thus allowing us to fit self-field critical current data. In this way we extract from the T-dependent gap a set of key thermodynamic parameters, the ground-state penetration depth, energy gap and jump in electronic specific heat. Our fits to 79 available data sets, from zinc nanowires to compressed sulphur hydride with critical temperatures of 0.65 to 203 K, respectively, are excellent and the extracted parameters agree well with reported bulk values. Samples include thin films, wires or nanowires of single- or multi-band s-wave and d-wave superconductors of either type I or type II. For multiband or multiphase samples we accurately recover individual band contributions and phase fractions.Self-field critical current data for many different superconductors is fitted by calculating the London penetration depth from the temperature dependence of the superconducting energy gap. This allows key thermodynamic parameters to be determined including the jump in electronic specific heat. Fits to 79 data sets, from zinc nanowires to compressed sulphur hydride with Tc from 0.65 to 203 K, respectively, are excellent and extracted parameters agree well with reported values. PubDate: 2017-09-06T01:41:25.007695-05: DOI: 10.1002/andp.201700197

Abstract: The cover illustrates the link between fractional Schrödinger equation (FSE) and light propagation in honeycomb lattice. The left cone shows the propagation through the honeycomb lattice by exciting the Dirac cones, as highlighted by the flickers in the band structure. The right cone mimics the propagation according to the FSE. The two cones meet at the ring that illustrates the uniformity of them via the Dirac-Weyl equation. PubDate: 2017-09-06T01:06:02.079144-05: DOI: 10.1002/andp.201770070

Authors:Evaldas Stankevičius; Mantas Garliauskas, Mindaugas Gedvilas, Nikolai Tarasenko, Gediminas Račiukaitis Abstract: Here, the structuring of surfaces with gold nanoparticles by using Bessel-like beam array is demonstrated. The experimental results show that the fabricated microring structures containing gold nanoparticles have a surface plasmon resonance in the spectral range of 520–540 nm, which can be tuned by selecting the laser treatment parameters. Fabricated microring structures exhibit a lower light transmittance comparing with the randomly distributed gold nanoparticles for wavelengths 500–570 nm due to the growth in the size of nanoparticles. In the spectral range of 600–700 nm, the light transmittance through microring structures is higher compared with the randomly distributed gold nanoparticles because of the removal of gold nanoparticles as gold has high reflectivity for wavelengths longer than 600 nm. The demonstrated method enables an easy fabrication of microring structures having tunable plasmonic properties.Fabrication of multi-ring structures consisting of gold nanoparticles is presented. Ring structures of gold nanoparticles with micron scale widths and millimeter scale lengths can induce localized surface plasmon resonance. The localized surface plasmon resonance coupling possessed by the ring-typed structure can significantly enhance fluorescence intensities and surface enhanced Raman spectroscopy signals. Furthermore, fabricated structures may find broad applications in near-field imaging, sensing, lithography and nanoparticle manipulations. PubDate: 2017-09-05T11:57:57.665729-05: DOI: 10.1002/andp.201700174

Authors:Anastasia Sokolova; Franziska Kilchert, Stefan Link, Alexander Stöhr, Ulrich Starke, M. Alexander Schneider Abstract: We deposited metals (Ti, Co, Pd) typically used as seed layers for contacts on epitaxial graphene on SiC(0001) and studied the early stages of growth in the sub-monolayer regime by Scanning Tunneling Microscopy (STM). All three metals do not wet the substrate and Ostwalt ripening occurs at temperatures below 400 K. The analysis of the epitaxial orientation of the metal adislands revealed their specific alignment to the graphene lattice. It is found that the apparent height of the islands as measured by STM strongly deviates from their true topographic height. This is interpreted as an indication of the presence of scattering processes within the metal particles that increase the transparency of the metal-graphene interface for electrons. Even large islands are easily picked up by the tip of the STM allowing insight into the bonding between metal island and graphene surface and into mechanisms leading to metal intercalation.For future graphene electronic devices contacts to the one-atom-thick sheet are of paramount importance. We studied the growth of typical seed metals (Co, Pd, and Ti) on epitaxial graphene and found that they do not wet the graphene surface but form three-dimensional islands with well-defined crystallographic orientation. When the islands are picked up by an STM tip, Co and Pd leave the graphene layer largely undisturbed while it is often destroyed underneath Ti. PubDate: 2017-09-05T11:56:42.668633-05: DOI: 10.1002/andp.201700031

Authors:Borzoo Nazari Abstract: The energy of the massless scalar field inside parallel Casimir plates in a general weak gravitational field under the influence of Robin boundary conditions is calculated. The mode frequencies are found in asymptotic limits and consistency of results with the literature is shown. Experimental evidence for detection of corrections is explored.The Casimir effect is a famous quantum field theoretical phenomenon under external boundary conditions. We study the influence of a general gravitational field on the Casimir plates for Robin boundary conditions. The induced corrections on mode frequencies and energy inside the plates can be used to put constraints on the local behavior of the modified gravitational theories. PubDate: 2017-09-05T11:55:42.797605-05: DOI: 10.1002/andp.201700142

Authors:Michele Merano Abstract: A classical theory of a radiating two-dimensional crystal is proposed and an expression for the radiation-reaction electric field is derived. This field plays an essential role in connecting the microscopic electromagnetic fields acting on each dipole of the crystal to the macroscopic one, via the boundary conditions for the system. The expression of the radiative-reaction electric field coincides with the macroscopic electric field radiating from the crystal and, summed to the incident electric field, generates the total macroscopic electric field.As for a three-dimensional solid, a local electromagnetic field acts on each atom or molecule in a two-dimensional crystal. Thus, the question that arises is how to go from the microscopic description to the macroscopic one. Surprisingly these two descriptions are connected via the radiative-reaction electric field felt by each microscopic constituent. PubDate: 2017-09-05T11:55:33.015045-05: DOI: 10.1002/andp.201700062

Authors:Xiaohu Zhang; Mingbo Pu, Jinjin Jin, Xiong Li, Ping Gao, Xiaoliang Ma, Changtao Wang, Xiangang Luo Abstract: The photonic spin-orbit interaction (PSOI) in inhomogeneous anisotropic metasurface has drawn much attentions recently due to its superior ability to manipulate light wave in the deep-subwavelength scale. Traditional methods involving PSOI are limited to operational spectral bandwidth owing to the intrinsic dispersion of the constitutive materials. In this paper, a helicity-multiplexing scheme is proposed to achieve independent control of the PSOI in both the spectral and spatial domains by combining the broadband characteristic with polarization dependence of the metasurface. Two simultaneous functions of multicolor holographic display and polarization encryption are experimentally demonstrated with a single metasurface perforated with nanoholes. Although the optical response of the nanoholes themselves are almost independent of the light wavelength, the obtained image can have abundant spectral information. The approach proposed here is promising for realizing multifunction optical device, multicolor display, optical storage and information encryption.A helicity multiplexed scheme is proposed by combining the broadband characteristic with polarization dependence of the anisotropic metasurface consisted of elongated nanoapertures. Two different functions, the multicolor holographic display and polarization encryption, are experimentally demonstrated simultaneously by a single metasurface. The proposed method has enormous potential applications in multicolor display, multifunction device and encryption technology etc. PubDate: 2017-09-04T08:26:05.970351-05: DOI: 10.1002/andp.201700248

Authors:Andrey Turchanin Abstract: Despite present diversity of graphene production methods there is still a high demand for improvement of the existing production schemes or development of new. Here a method is reviewed to produce graphene employing aromatic self-assembled monolayers (SAMs) as molecular precursors. This method is based on electron irradiation induced crosslinking of aromatic SAMs resulting in their conversion into carbon nanomembranes (CNMs) with high thermal stability and subsequent pyrolysis of CNMs into graphene in vacuum or in the inert atmosphere. Depending on the production conditions, such as chemical structure of molecular precursors, irradiation and annealing parameters, various properties of the produced graphene sheets including shape, crystallinity, thickness, optical properties and electric transport can be adjusted. The assembly of CNM/graphene van der Waals heterostructures opens a flexible route to non-destructive chemical functionalization of graphene for a variety of applications in electronic and photonic devices.A method is reviewed to produce graphene employing aromatic self-assembled monolayers as molecular precursors. This method is based on the electron irradiation induced chemical reactions and pyrolysis. As shown by complementary spectroscopic, microscopic and electric transport measurements and theoretical analysis, shape, crystallinity, thickness, optical and electronic properties of the graphene sheets can flexibly be adjusted depending on the production conditions. Novel possibilities of the developed method for nanotechnology are discussed. PubDate: 2017-08-31T08:27:44.228864-05: DOI: 10.1002/andp.201700168

Authors:Stefan Meinecke; Benjamin Lingnau, André Röhm, Kathy Lüdge Abstract: Simultaneous two-state lasing is a unique property of semiconductor quantum-dot (QD) lasers. This not only changes steady-state characteristics of the laser device but also its dynamic response to perturbations. In this paper we investigate the dynamic stability of QD lasers in an external optical injection setup. Compared to conventional single-state laser devices, we find a strong suppression of dynamical instabilities in two-state lasers. Furthermore, depending on the frequency and intensity of the injected light, pronounced areas of bistability between both lasing frequencies appear, which can be employed for fast optical switching in all-optical photonic computing applications. These results emphasize the suitability of QD semiconductor lasers in future integrated optoelectronic systems where a high level of stability is required.Semiconductor lasers with quantum-dots as active material are able to simultaneously lase at two wavelength. They can be exploited for all-optical switching applications, if implemented in an optical injection setup. We analyse the stability properties and discuss the parameter dependence of the bi-stability regions between ground-state (GS) and excited-state (ES) emission. Interestingly, a large tolerance to optical perturbations is found for these two-state lasers. PubDate: 2017-08-28T04:57:02.685952-05: DOI: 10.1002/andp.201600279

Authors:Stephan Winnerl; Martin Mittendorff, Jacob C. König-Otto, Harald Schneider, Manfred Helm, Torben Winzer, Andreas Knorr, Ermin Malic Abstract: A joint experiment-theory investigation of the carrier dynamics in graphene, in particular in the energetic vicinity of the Dirac point, is reviewed. Radiation of low photon energy is employed in order to match the intrinsic energy scales of the material, i.e. the optical phonon energy (∼200 meV) and the Fermi energy (10-20 meV), respectively. Significant slower carrier cooling is predicted and observed for photon energies below the optical phonon energy. Furthermore, a strongly anisotropic distribution of electrons in k-space upon excitation with linearly polarized radiation is discussed. Depending on photon energy, the anisotropic distribution decays either rapidly via optical phonon emission, or slowly via non-collinear Coulomb scattering. Finally, a room temperature operated ultra-broadband hot-electron bolometer is demonstrated. It covers the spectral range from the THz to visible region with a single detector element featuring a response time of 40 ps.The carrier dynamics in graphene is investigated in a joint experiment-theory study, with a particular focus on optical excitations at low energies. The role of carrier-phonon and carrier-carrier scattering is clearly disentangled and a twofold behavior for carrier-carrier scattering is revealed: (i) fast collinear scattering and (ii) comparably slow non-collinear scattering. Furthermore fast ultrabroadband detectors, covering the range from THz to visible, are demonstrated. PubDate: 2017-08-23T12:27:35.622518-05: DOI: 10.1002/andp.201700022

Authors:Felix Schwarz; Erich Runge Abstract: The potential of disorder to confine and enhance electromagnetic fields is well known and localized fields in turn can be used for non-linear optical sensing and for studying quantum optics. Recently, nanoporous gold nanoparticles (nanosponges) were shown to support highly localized long-lived plasmonic modes in the infrared spectral range. In this paper, we take first steps towards tailoring the disorder for optimal field localization and enhancement by calculating extinction and near-field properties for different filling fractions and correlation lengths. We find that the filling fraction has not only a large effect on the fundamental dipolar surface-plasmon resonance of the nanoparticle, but also on the frequency range in which localized modes of plasmonic nature occur. The influence of the correlation length is more subtle but is seen to influence the coupling between localized and far-field modes as well. We briefly discuss first results on details of the localization process, which takes place on the same length scale as the typical structure size, so a simple cavity-resonance picture cannot account for the relatively low frequency of the modes.Nanoporous gold nanoparticles (nanosponges) intrinsically confine and enhance electromagnetic fields as plasmonic modes on a length scale given by the pore size, which is well below optical wavelengths. This opens new routes towards, e.g., non-linear optical sensing and nano-scale quantum optics. A numerical study varies filling fractions and feature size of the gold sponges in order to understand and optimize the presence of long-lived ultra-localized plasmonic modes. PubDate: 2017-08-23T12:26:58.284084-05: DOI: 10.1002/andp.201600234

Authors:Patrick Zeller; Michael Weinl, Florian Speck, Markus Ostler, Ann-Kathrin Henß, Thomas Seyller, Matthias Schreck, Joost Wintterlin Abstract: Single crystalline metal films deposited on YSZ-buffered Si(111) wafers were investigated with respect to their suitability as substrates for epitaxial graphene. Graphene was grown by CVD of ethylene on Ru(0001), Ir(111), and Ni(111) films in UHV. For analysis a variety of surface science methods were used. By an initial annealing step the surface quality of the films was strongly improved. The temperature treatments of the metal films caused a pattern of slip lines, formed by thermal stress in the films, which, however, did not affect the graphene quality and even prevented wrinkle formation. Graphene was successfully grown on all three types of metal films in a quality comparable to graphene grown on bulk single crystals of the same metals. In the case of the Ni(111) films the originally obtained domain structure of rotational graphene phases could be transformed into a single domain by annealing. This healing process is based on the control of the equilibrium between graphene and dissolved carbon in the film. For the system graphene/Ni(111) the metal, after graphene growth, could be removed from underneath the epitaxial graphene layer by a pure gas phase reaction, using the reaction of CO with Ni to give gaseous Ni(CO)4.A special type of metal substrate has been used to grow monolayer graphene by CVD of hydrocarbons. The substrates consist of 100 to 150 nm thin films of ruthenium, iridium, and nickel, supported on YSZ-buffered Si(111). The films are single-crystalline and available as 4 inch wafers, providing a possibly upscalable route to lattice-oriented graphene. PubDate: 2017-08-14T02:07:36.11311-05:0 DOI: 10.1002/andp.201700023

Authors:Ermin Malic; Gunnar Berghäuser, Maja Feierabend, Andreas Knorr Abstract: Chemical functionalization of atomically thin nanostructures presents a promising strategy to create new hybrid nanomaterials with remarkable and externally controllable properties. Here, we review our research in the field of theoretical modeling of carbon nanotubes, graphene, and transition metal dichalcogenides located in molecular dipole fields. In particular, we provide a microscopic view on the change of the optical response of these technologically promising nanomaterials due to the presence of photo-active spiropyran molecules. The feature article presents a review of recent theoretical work providing microscopic view on the optical response of chemically functionalized carbon nanotubes, graphene, and monolayered transition metal dichalcogenides. In particular, we propose a novel sensor mechanism based on the molecule-induced activation of dark excitons. This results in a pronounced additional peak presenting an unambiguous optical fingerprint for the attached molecules.The feature article presents a review of recent theoretical work providing microscopic view on the optical response of chemically functionalized carbon nanotubes, graphene, and monolayered transition metal dichalcogenides. In particular, we propose a novel sensor mechanism based on the molecule-induced activation of dark excitons. This results in a pronounced additional peak presenting an unambiguous optical fingerprint for the attached molecules. PubDate: 2017-08-14T02:06:46.364883-05: DOI: 10.1002/andp.201700097

Authors:Stefan G. Fischer; Clemens Gneiting, Andreas Buchleitner Abstract: We systematically derive the semiclassical limit of a charged particle's motion in the presence of an infinitely long and infinitesimally thin solenoid carrying magnetic flux. Our limit establishes the connection of the particle's quantum mechanical canonical angular momentum to the latter's classical counterpart. A picture of Aharonov-Bohm interference of two half-waves acquiring Dirac's magnetic phase when passing on either side of the solenoid naturally emerges from the quantum propagator. The resulting interference pattern is fully determined by the ratio of the angular part of Hamilton's principal function to Planck's constant, and the wave interference smoothes out discontinuities in the semiclassical propagator which is recovered in the limit when the above ratio diverges. We discuss the relation of our results to the whirling-wave representation of the exact propagator, and to previous approaches on the system's asymptotics.A novel derivation of the semiclassical limit is presented for a particle propagating in the presence of an Aharonov-Bohm vector potential. The derivation shows how the quantum mechanical canonical angular momentum is transformed into the latter's classical counterpart, and a characteristic half-wave interference pattern naturally emerges in an intermediate stage of the limiting procedure. PubDate: 2017-08-14T02:05:50.105018-05: DOI: 10.1002/andp.201700120

Authors:Alexander Stöhr; Jens Baringhaus, Johannes Aprojanz, Stefan Link, Christoph Tegenkamp, Yuran Niu, Alexei A. Zakharov, Chaoyu Chen, José Avila, Maria C. Asensio, Ulrich Starke Abstract: Structured Silicon Carbide was proposed to be an ideal template for the production of arrays of edge specific graphene nanoribbons (GNRs), which could be used as a base material for graphene transistors. We prepared periodic arrays of nanoscaled stripe-mesas on SiC surfaces using electron beam lithography and reactive ion etching. Subsequent epitaxial graphene growth by annealing is differentiated between the basal-plane mesas and the faceting stripe walls as monitored by means of atomic force microscopy (AFM). Microscopic low energy electron diffraction (μ-LEED) revealed that the graphene ribbons on the facetted mesa side walls grow in epitaxial relation to the basal-plane graphene with an armchair orientation at the facet edges. The π-band system of the ribbons exhibits linear bands with a Dirac like shape corresponding to monolayer graphene as identified by angle-resolved photoemission spectroscopy (ARPES).Epitaxial graphene nanoribbons are prepared on lithographically structured Silicon Carbide. The ribbons grow on the facetted mesa side walls in epitaxial relation to the basal-plane graphene. In angle-resolved photoemission spectroscopy (ARPES) the π- electrons from the ribbons display a sharp band and emerge at a distinctly different emission angle compared to the basal-plane graphene. PubDate: 2017-08-09T06:30:32.972227-05: DOI: 10.1002/andp.201700052

Authors:Massimiliano Di Ventra; Fabio L. Traversa, Igor V. Ovchinnikov Abstract: It is well known that dynamical systems may be employed as computing machines. However, not all dynamical systems offer particular advantages compared to the standard paradigm of computation, in regard to efficiency and scalability. Recently, it was suggested that a new type of machines, named digital –hence scalable– memcomputing machines (DMMs), that employ non-linear dynamical systems with memory, can solve complex Boolean problems efficiently. This result was derived using functional analysis without, however, providing a clear understanding of which physical features make DMMs such an efficient computational tool. Here, we show, using recently proposed topological field theory of dynamical systems, that the solution search by DMMs is a composite instanton. This process effectively breaks the topological supersymmetry common to all dynamical systems, including DMMs. The emergent long-range order – a collective dynamical behavior– allows logic gates of the machines to correlate arbitrarily far away from each other, despite their non-quantum character. We exemplify these results with the solution of prime factorization, but the conclusions generalize to DMMs applied to any other Boolean problem.Digital memcomputing machines are dynamical systems that can solve complex problems efficiently. Their computational power originates from a transient instantonic phase that creates non-locality in the system. The instantons connect topologically inequivalent critical points in the phase space as shown in the schematic. PubDate: 2017-08-07T01:40:48.153723-05: DOI: 10.1002/andp.201700123

Authors:Zhi Chen; Concepción Molina-Jirón, Svetlana Klyatskaya, Florian Klappenberger, Mario Ruben Abstract: In solution-based chemistry butadiyne linkage through the homocoupling reaction of alkynes is a versatile tool for the synthesis of π-conjugated polymers, scaffolds and networks. To date this strategy was actively implemented towards chemical synthesis at interfaces. In this review paper we summarize recent advances in the syntheses of 1D wires, 2D single-layers and thin films of graphdiyne-related carbon materials at interfaces and their potential applications in nanotechnology. With a high degree of π-conjunction, uniformly distributed pores and tunable electronic properties such 2D all-carbon networks with butadiyne linkages also known as ‘graphdiynes’ have been successfully employed in the field-effected emission devices, solar cells, for Li ion storage and oil water separation, and as catalysis or chemical sensors.Recent advances in the syntheses of 1D wires, 2D single layers, and 3D-graphdiyne materials at interfacess and the potential applications of the obtained materials in devices have been summarized. PubDate: 2017-07-31T02:17:38.345916-05: DOI: 10.1002/andp.201700056

Authors:T. Finge; F. Riederer, M. R. Mueller, T. Grap, K. Kallis, J. Knoch Abstract: In the present article, experimental and theoretical investigations regarding field-effect transistors based on two-dimensional (2D) materials are presented. First, the properties of contacts between a metal and 2D material are discussed. To this end, metal-to-graphene contacts as well to transition metal dichalcogenides (TMD) are studied. Whereas metal-graphene contacts can be tuned with an appropriate back-gate, metal-TMD contacts exhibit strong Fermi level pinning showing substantially limited maximum possible drive current. Next, tungsten diselenide (WSe2) field-effect transistors are presented. Employing buried-triple-gate substrates allows tuning source, channel and drain by applying appropriate gate voltages so that the device can be reconfigured to work as n-type, p-type and as so-called band-to-band tunnel field-effect transistor on the same WSe2 flake.Two-dimensional (2D) materials are being considered ideally suited for ultimately scaled field-effect transistor devices due to their extremely thin thickness and excellent electronic transport properties. Realizing appropriate contacts and doped source/drain regions is, however, difficult. Multigate substrates are being employed here, that allow generating potential landscapes within 2D field-effect transistor devices facilitating electronic transport studies as well as the realization of reconfigurable device functionalities. PubDate: 2017-07-31T02:16:31.248695-05: DOI: 10.1002/andp.201700087

Authors:Johannes C. Rode; Dmitri Smirnov, Christopher Belke, Hennrik Schmidt, Rolf J. Haug Abstract: Twisted Bilayer Graphene may be viewed as very first representative of the now booming class of artificially layered 2D materials. Consisting of two sheets from the same structure and atomic composition, its decisive degree of freedom lies in the rotation between crystallographic axes in the individual graphene monolayers. Geometrical consideration finds angle-dependent Moiré patterns as well as commensurate superlattices of opposite sublattice exchange symmetry. Beyond the approach of rigidly interposed lattices, this review takes focus on the evolving topic of lattice corrugation and distortion in response to spatially varying lattice registry. The experimental approach to twisted bilayers requires a basic control over preparation techniques; important methods are summarized and extended on in the case of bilayers folded from monolayer graphene via AFM nanomachining. Central morphological parameters to the twisted bilayer, rotational mismatch and interlayer separation are studied in a broader base of samples. Finally, experimental evidence for a number of theoretically predicted, controversial electronic scenarios are reviewed; magnetotransport signatures are discussed in terms of Fermi velocity, van Hove singularities and Berry phase and assessed with respect to the underlying experimental conditions, thereby referring back to the initially considered variations in relaxed lattice structure.Twisted bilayer graphene (TBG) consists of a stack of two rotationally misaligned monolayer lattices. This article reviews the current state of the art in preparation as well as characterization of TBG. Special focus is directed towards the preparation technique of folding monolayer graphene via Atomic Force Microscope and investigation of resulting TBG morphology. Different electronic coupling scenarios, as inferred from magnetotransport measurements, are furthermore evaluated under consideration of superlattice corrugation. PubDate: 2017-07-31T02:15:58.78941-05:0 DOI: 10.1002/andp.201700025

Authors:D. N. Makarov Abstract: At present, the sources of entangled photons have a low rate of photon generation. This limitation is a key component of quantum informatics for the realization of such functions as linear quantum computation and quantum teleportation. In this paper, we propose a method for high intensity generation of entangled photons in a two-mode electromagnetic field. On the basis of exact solutions of the Schrödinger equation, when electrons interact in an atom with a strong two-mode electromagnetic field, it is shown that there may be large quantum entanglement between photons. The quantum entanglement is analyzed on the basis of the Schmidt parameter. It is shown that the Schmidt parameter can reach very high values depending on the choice of characteristics of the two-mode fields. We find the Wigner function for the considered case. Violation of Bell's inequalities for continuous variables is demonstrated.At present, the sources of entangled photons have a low rate of photon generation. This limitation is a key component of quantum informatics for the realization of such functions as linear quantum computation and quantum teleportation. In this paper, the authors propose a method for high intensity generation of entangled photons in a two-mode electromagnetic field. PubDate: 2017-07-31T02:10:57.759456-05: DOI: 10.1002/andp.201600408

Authors:A. Vagov; M. D. Croitoru, I. A. Larkin, V. M. Axt Abstract: This work investigates the influence of non-locality in the dielectric response on the spatio-temporal evolution of surface plasmon-polaritons (SPP). SPP excitations are coherently generated by a quantum scatterer in the vicinity of a flat metal interface. It is demonstrated that the excited non-equilibrium SPP population eventually splits into two coherent localized wave packets. One packet propagates along the interface and the other is centered in the vicinity of the scatter. The amplitude of both waves slowly decreases due to several relaxation mechanisms, with the Landau damping being the strongest. The non-locality of the metallic dielectric response considerably influences spatial profiles of the plasmon field intensity, in particular, leading to coherent spatio-temporal oscillations between the two wave packets.Generation of surface plasmons becomes highly non-trivial when a quantum scatterer is strongly coupled to the metallic surface. In this case Rabi oscillations in the dynamics of the scatterer are imprinted in the spatial distribution of the plasmon wave packets. Quantum correlations between the scatterer and plasmons are manifested in spatial oscillations of the field profile. They persist at large distances and affect the plasmon propagation. PubDate: 2017-07-31T02:10:48.690045-05: DOI: 10.1002/andp.201600387

Authors:A. V. Syromyatnikov Abstract: We discuss a quantum transition from a superfluid to a Mott glass phases in disordered Bose-systems by the example of an isotropic spin-12 antiferromagnet with spatial dimension d≥2 and with disorder in tunable exchange couplings. Our analytical consideration is based on general properties of a system in critical regime, on the assumption that the magnetically order part of the system shows fractal properties near the transition, and on a hydrodynamic description of long-wavelength magnons in the magnetically ordered (“superfluide”) phase. Our results are fully consistent with a scaling theory based on an ansatz for the free energy proposed by M. P. Fisher et al. (Phys. Rev. B 40, 546 (1989)). We obtain z=d−β/ν for the dynamical critical exponent and ϕ=zν, where ϕ, β, and ν are critical exponents of the critical temperature, the order parameter, and the correlation length, respectively. The density of states of localized excitations (fractons) is found to show a superuniversal (i.e., independent of d) behavior.The interplay of quantum fluctuations and quenched disorder leads to a variety of unconventional phenomena and special quantum phases. The author discusses a quantum transition from a magnetically ordered to a Mott glass phases in an isotropic spin-1/2 antiferromagnet with disorder in tunable exchange couplings. Results obtained should be relevant to various Bose-systems from the same universality class. A new method is used for consideration of this transition. PubDate: 2017-07-31T02:10:32.778092-05: DOI: 10.1002/andp.201700055

Authors:Adeline Crépieux Abstract: The electrical and heat currents flowing through a quantum dot are calculated in the presence of a time-modulated gate voltage with the help of the out-of-equilibrium Green function technique. From the first harmonics of the currents, we extract the electrical and thermoelectrical trans-admittances and ac-conductances. Next, by a careful comparison of the ac-conductances with the finite-frequency electrical and mixed electrical-heat noises, we establish the fluctuation-dissipation relations linking these quantities, which are thus generalized out-of-equilibrium for a quantum system. It is shown that the electrical ac-conductance associated to the displacement current is directly linked to the electrical noise summed over reservoirs, whereas the relation between the thermoelectrical ac-conductance and the mixed noise contains an additional term proportional to the energy step that the electrons must overcome when traveling through the junction. A numerical study reveals however that a fluctuation-dissipation relation involving a single reservoir applies for both electrical and thermoelectrical ac-conductances when the frequency dominates over the other characteristic energies.The fluctuation-dissipation theorem linking dc-noise with ac-conductance at equilibrium is well known and widely used. How this relation generalizes out-of-equilibrium' By calculating the time-dependent Keldysh Green functions, it is shown here that one has to sum over noises in both source and drain reservoirs to obtain such a relationship. The existence of a similar relation between thermoelectrical ac-conductance and mixed noise is also questioned. PubDate: 2017-07-26T01:15:36.372193-05: DOI: 10.1002/andp.201600344

Authors:Sowmya Somanchi; Bernat Terrés, Julian Peiro, Maximilian Staggenborg, Kenji Watanabe, Takashi Taniguchi, Bernd Beschoten, Christoph Stampfer Abstract: Graphene nanoribbons and constrictions are envisaged as fundamental components of future carbon-based nanoelectronic and spintronic devices. At nanoscale, electronic effects in these devices depend heavily on the dimensions of the active channel and the nature of edges. Hence, controlling both these parameters is crucial to understand the physics in such systems. This review is about the recent progress in the fabrication of graphene nanoribbons and constrictions in terms of low temperature quantum transport. In particular, recent advancements using encapsulated graphene allowing for quantized conductance and future experiments towards exploring spin effects in these devices are presented. The influence of charge carrier inhomogeneity and the important length scales which play a crucial role for transport in high quality samples are also discussed.Recent technological developments allow the fabrication of etched high-quality graphene nanoconstrictions and nanoribbons that exhibit ballistic transport and quantized conductance. Transport through such devices depends crucially on the nature of edges and localized edge states. By incorporating local top gates, the influence of the localized edge states can be independently tuned from the transmission of the ballistic channel in such devices (see Figure). PubDate: 2017-07-26T01:11:17.692287-05: DOI: 10.1002/andp.201700082

Authors:Carsten Honerkamp Abstract: We investigate the impact of electron self-energy corrections on potential antiferromagnetic ordering instabilities in mono- and bilayer graphene, modeled by a Hubbard-type lattice model with onsite interactions among the electrons, using a self-consistent random phase approximation (RPA). In qualitative agreement with earlier studies we find that the electronic interactions cause non-Fermi liquid behavior at low energies. In self-consistent RPA, the transition scales for antiferromagnetic ordering are renormalized significantly by these self-energy effects, both for interaction-driven and temperature-driven cases.Meanfield or random phase approximations (RPA) are widely used to investigate symmetry breaking due to interaction effects in many fermion lattice models, e.g. in models for graphene. While it is known that these approximations overestimate ordering, the quantitative error is rarely estimated. Here the authors incorporate selfenergy effects describing quasiparticle degradation into the RPA analysis. The authors find marked reductions of the temperature scales where the ordering tendencies become strong. PubDate: 2017-07-26T01:10:40.868115-05: DOI: 10.1002/andp.201700044

Authors:Matthias M. Müller; Stefano Gherardini, Filippo Caruso Abstract: Quantum measurements play a crucial role in quantum mechanics since they perturb, unavoidably and irreversibly, the state of the measured quantum system. More extremely, the constant observation of a quantum system can even freeze its dynamics to a subspace, effectively truncating the Hilbert space of the system. It represents the quantum version of the famous flying arrow Zeno paradox, and is called quantum Zeno dynamics. In general, it can be obtained by applying frequent consecutive quantum measurements that are equally spaced in time. Here, we introduce time disorder in the measurement sequence, and analytically investigate how this temporal stochasticity may affect the confinement probability of the system in the subspace. As main result, we then exploit how different dissipative and coherent Zeno protocols can be generalized to this stochastic scenario. Finally, our analytical predictions are numerically tested on a paradigmatic spin chain where we find a trade-off between a probabilistic scheme with high fidelity (compared to perfect subspace dynamics) and a deterministic one with a slightly lower fidelity, moving further steps towards new schemes of Zeno-based control for future quantum technologies.The authors discuss effects of localization in a many-body system subjected to random interaction. For a spin chain we investigate different protocols of coherent and dissipative control to confine the dynamics of the system, effectively implementing a stochastic version of so-called Quantum Zeno dynamics. PubDate: 2017-07-21T07:15:35.699022-05: DOI: 10.1002/andp.201600206

Authors:Zhansong Geng; Bernd Hähnlein, Ralf Granzner, Manuel Auge, Alexander A. Lebedev, Valery Y. Davydov, Mario Kittler, Jörg Pezoldt, Frank Schwierz Abstract: Graphene nanoribbons show unique properties and have attracted a lot of attention in the recent past. Intensive theoretical and experimental studies on such nanostructures at both the fundamental and application-oriented levels have been performed. The present paper discusses the suitability of graphene nanoribbons devices for nanoelectronics and focuses on three specific device types – graphene nanoribbon MOSFETs, side-gate transistors, and three terminal junctions. It is shown that, on the one hand, experimental devices of each type of the three nanoribbon-based structures have been reported, that promising performance of these devices has been demonstrated and/or predicted, and that in part they possess functionalities not attainable with conventional semiconductor devices. On the other hand, it is emphasized that – in spite of the remarkable progress achieved during the past 10 years – graphene nanoribbon devices still face a lot of problems and that their prospects for future applications remain unclear.Graphene nanoribbons (GNRs) show unique properties and may constitute the basic components of future nanoelectronic systems. In the present work, the state of the art, the merits, and also the drawbacks of three types of GNR devices – GNR MOSFETs, GNR side-gate FETs, and GNR three terminal junctions, see figure on the left – are examined and the potential of these devices for future nanoelectronics is discussed. PubDate: 2017-07-21T05:47:00.971282-05: DOI: 10.1002/andp.201700033

Authors:Chang-Chun Ding; Qin-Sheng Zhu, Shao-Yi Wu, Wei Lai Abstract: A two qubits system interacting with two independent spin-environments connecting with the third environment is constructed in order to demonstrate the effect of the multi-environment for quantum correlation. In this process, the freezing phenomenon appears for SCI and X states under Quantum Discord and Geometric Discord measures, respectively, but not for the same initial state measured by different measures. Meanwhile, the properties of the freezing platform, characterized by the collapse, revival and persistent time, are researched by the different parameters. The result of this paper may pave a way to control quantum correlation and design nanospintronic devices.The interacting muti-environment affects the properties of quantum correlation, even some environments do not directly interact with the system. The freezing behavior emerges only by the QD or GD method under the same condition and can be effectively affected by the intrinsic parameters (the coupling parameter b between the spin particles and environments, the environments temperature T and the coupling parameters q between the environments). PubDate: 2017-07-20T08:37:08.874168-05: DOI: 10.1002/andp.201700014

Authors:D. Felbacq; E. Rousseau Abstract: Metamaterials made of periodic collections of dielectric nanorods are considered theoretically. When quantum resonators are embedded within the nanorods, one obtains a quantum metamaterial, whose electromagnetic properties depend upon the state of the quantum resonators. The theoretical model predicts that when the resonators are pumped and reach the inversion regime, the quantum metamaterial exhibits an all-optical switchable conduction band. The phenomenon can be described by considering the pole stucture of the scattering matrix of the metamaterial.Quantum metamaterials are metamaterials in which quantum degrees of freedom are inserted. Such a metamaterial comprising quantum dots is presented. It is predicted that there exists a photonic conduction band that can be switched on and off by using an external pump field that serve to saturate the quantum dots and reach the emission regime. PubDate: 2017-07-17T03:42:16.574003-05: DOI: 10.1002/andp.201600371

Authors:Manoel P. Araújo; Stefano Leo, Gabriel G. Maia Abstract: We analyze and compare the angular deviations for an optical beam reflected by and transmitted through a dielectric triangular prism. The analytic expressions derived for the angular deviations hold for arbitrary incidence angles. For incidence approaching the internal and external Brewster angles, the angular deviations transverse magnetic waves present the same behavior leading to the well-known giant Goos-Hänchen angular shift. For incidence near the critical angle a new region of large shift is seen both for transverse magnetic and transverse electric waves. While a direct measuring procedure is better in the vicinity of the Brewster region, a weak measurement breaks off the giant Goos-Hänchen effect, preserving the amplification in the critical region. We discuss under which conditions it is possible to optimize the amplification and we also determine when a weak measurement is preferred to a direct measuring procedure.Angular deviations of a beam transmitted through a triangular dielectric block have been theoretically studied and related analytical expressions have been found. Using these analytical expresssions, the weak measurement procedure has been optimized showing a breaking off in the Brewester region and an effective amplification for incidence near the critical angle. PubDate: 2017-07-17T03:41:58.035014-05: DOI: 10.1002/andp.201600357

Authors:Juan Jose Mendoza-Arenas; Fernando Javier Gómez-Ruiz, Martin Eckstein, Dieter Jaksch, Stephen R. Clark Abstract: Motivated by cold atom and ultra-fast pump-probe experiments we study the melting of long-range antiferromagnetic order of a perfect Néel state in a periodically driven repulsive Hubbard model. The dynamics is calculated for a Bethe lattice in infinite dimensions with non-equilibrium dynamical mean-field theory. In the absence of driving melting proceeds differently depending on the quench of the interactions to hopping ratio U/ν0 from the atomic limit. For U≫ν0 decay occurs due to mobile charge-excitations transferring energy to the spin sector, while for ν0≳U it is governed by the dynamics of residual quasi-particles. Here we explore the rich effects that strong periodic driving has on this relaxation process spanning three frequency ω regimes: (i) high-frequency ω≫U,ν0, (ii) resonant lω=U>ν0 with integer l, and (iii) in-gap U>ω>ν0 away from resonance. In case (i) we can quickly switch the decay from quasi-particle to charge-excitation mechanism through the suppression of ν0. For (ii) the interaction can be engineered, even allowing an effective U=0 regime to be reached, giving the reverse switch from a charge-excitation to quasi-particle decay mechanism. For (iii) the exchange interaction can be controlled with little effect on the decay. By combining these regimes we show how periodic driving could be a potential pathway for controlling magnetism in antiferromagnetic materials. Finally, our numerical results demonstrate the accuracy and applicability of matrix product state techniques to the Hamiltonian DMFT impurity problem subjected to strong periodic driving.Motivated by state-of-the-art experiments on ultra-fast control of many-body quantum systems, the dynamics of a periodically-driven Hubbard lattice is analyzed in an infinite-dimensional Bethe geometry. Its evolution from an antiferromagetic state is simulated by combining nonequilibrium DMFT with a MPS impurity solver. Tuning the driving frequency, magnetic melting slowdown (high frequency), enhancement and dynamics reversal (resonance) are induced. Periodic driving thus provides a pathway for manipulating magnetism in complex systems. PubDate: 2017-07-17T03:41:12.688786-05: DOI: 10.1002/andp.201700024

Authors:Markus Morgenstern; Nils Freitag, Alexander Nent, Peter Nemes-Incze, Marcus Liebmann Abstract: Scanning tunneling spectroscopy results probing the electronic properties of graphene quantum dots are reviewed. After a short summary of the study of squared wave functions of graphene quantum dots on metal substrates, we firstly present data where the Landau level gaps caused by a perpendicular magnetic field are used to electrostatically confine electrons in monolayer graphene, which are probed by the Coulomb staircase revealing the consecutive charging of a quantum dot. It turns out that these quantum dots exhibit much more regular charging sequences than lithographically confined ones. Namely, the consistent grouping of charging peaks into quadruplets, both, in the electron and hole branch, portrays a regular orbital splitting of about 10meV. At low hole occupation numbers, the charging peaks are, partly, additionally grouped into doublets. The spatially varying energy separation of the doublets indicates a modulation of the valley splitting by the underlying BN substrate. We outline that this property might be used to eventually tune the valley splitting coherently. Afterwards, we describe graphene quantum dots with multiple contacts produced without lithographic resist, namely by local anodic oxidation. Such quantum dots target the goal to probe magnetotransport properties during the imaging of the corresponding wave functions by scanning tunneling spectroscopy.Graphene quantum dots are promising as qubits, but currently still suffer from too much disorder. Using scanning tunneling spectroscopy in ultrahigh vacuum, the authors aim to overcome these problems, e.g., by electrostatically inducing quantum dots into monolayer graphene exploiting the gaps caused by Landau quantization. An extraordinary quality of charging patterns results including reliable orbital and valley splittings. The authors review these and other efforts to optimize graphene quantum dots within an ultraclean environment. PubDate: 2017-07-17T03:40:47.061385-05: DOI: 10.1002/andp.201700018

Authors:Florian Speck; Markus Ostler, Sven Besendörfer, Julia Krone, Martina Wanke, Thomas Seyller Abstract: Based on its electronic, structural, chemical, and mechanical properties, many potential applications have been proposed for graphene. In order to realize these visions, graphene has to be synthesized, grown, or exfoliated with properties that are determined by the targeted application. Growth of so-called epitaxial graphene on silicon carbide by sublimation of silicon in an argon atmosphere is one particular method that could potentially lead to electronic applications. In this contribution we summarize our recent work on different aspects of epitaxial graphene growth and interface manipulation by intercalation, which was performed by a combination of low-energy electron microscopy, low-energy electron diffraction, atomic force microscopy and photoelectron spectroscopy.The sublimation growth of epitaxial graphene on silicon carbide in an argon atmosphere is one particular synthesis method that could potentially lead to electronic applications. The paper summarizes recent work on different aspects of epitaxial graphene growth and interface manipulation by intercalation, which was performed by a combination of low-energy electron microscopy, low-energy electron diffraction, atomic force microscopy and photoelectron spectroscopy. PubDate: 2017-07-17T03:36:48.505472-05: DOI: 10.1002/andp.201700046

Authors:E. Malic; T. Winzer, F. Wendler, S. Brem, R. Jago, A. Knorr, M. Mittendorff, J. C. König-Otto, T. Plötzing, D. Neumaier, H. Schneider, M. Helm, S. Winnerl Abstract: Graphene is an ideal material to study fundamental Coulomb- and phonon-induced carrier scattering processes. Its remarkable gapless and linear band structure opens up new carrier relaxation channels. In particular, Auger scattering bridging the valence and the conduction band changes the number of charge carriers and gives rise to a significant carrier multiplication - an ultrafast many-particle phenomenon that is promising for the design of highly efficient photodetectors. Furthermore, the vanishing density of states at the Dirac point combined with ultrafast phonon-induced intraband scattering results in an accumulation of carriers and a population inversion suggesting the design of graphene-based terahertz lasers. Here, we review our work on the ultrafast carrier dynamics in graphene and Landau-quantized graphene is presented providing a microscopic view on the appearance of carrier multiplication and population inversion.The feature article presents a review of recent theoretical work providing microscopic view on the time- and energy-resolved dynamics of optically excited carriers in graphene. The remarkable gapless and linear band structure of graphene opens up new relaxation channels giving rise to fascinating ultrafast phenomena. In this work, the authors focus on the appearance of technologially relevant carrier multiplication and population inversion. PubDate: 2017-07-17T03:36:01.052022-05: DOI: 10.1002/andp.201700038

Authors:Enrique Maciá Abstract: A spectral classification of general one-dimensional binary aperiodic crystals (BACs) based on both their diffraction patterns and energy spectrum measures is introduced along with a systematic comparison of the zeroth-order energy spectrum main features for BACs belonging to different spectral classes, including Fibonacci-class, precious means, metallic means, mixed means and period doubling based representatives. These systems are described by means of mixed-type Hamiltonians which include both diagonal and off-diagonal terms aperiodically distributed. An algebraic approach highlighting chemical correlation effects present in the underlying lattice is introduced. Close analytical expressions are obtained by exploiting some algebraic properties of suitable blocking schemes preserving the atomic order of the original lattice. The existence of a resonance energy which defines the basic anatomy of the zeroth-order energy spectra structure for the standard Fibonacci, the precious means and the Fibonacci-class quasicrystals is disclosed. This eigenstate is also found in the energy spectra of BACs belonging to other spectral classes, but for specific particular choices of the corresponding model parameters only. The transmission coefficient of these resonant states is always bounded below, although their related Landauer conductance values may range from highly conductive to highly resistive ones, depending on the relative strength of the chemical bonds.A spectral classification of general one-dimensional binary aperiodic crystals based on both their diffraction and energy spectrum measures is introduced, along with an algebraic approach highlighting chemical correlation effects in the underlying lattice. A number of resonant energies, shared by systems belonging to different spectral classes, are disclosed. Their related Landauer conductance takes on either highly conductive or highly resistive values, depending on the relative strength of the chemical bonds. PubDate: 2017-07-17T03:30:52.700763-05: DOI: 10.1002/andp.201700079

Authors:Slava Emelyanov Abstract: We employ quantum kinetic theory to investigate local quantum physics in the background of spherically symmetric and neutral black holes formed through the gravitational collapse. For this purpose in mind, we derive and study the covariant Wigner distribution function W(x,p) near to and far away from the black-hole horizon. We find that the local density of the particle number is negative in the near-horizon region, while the entropy density is imaginary. These pose a question whether kinetic theory is applicable in the near-horizon region. We elaborate on that and propose a possible interpretation of how this result might nevertheless be self-consistently understood.Classical many-particle systems can be described with the help of macroscopic state variables: energy density, pressure, particle number density and so on. The authors employ relativistic kinetic theory to study local state variables in the background of an evaporating black hole. For that purpose, a distribution function characterising the black-hole evaporation is derived in the far-from- and near-horizon region. It is then used to examine local quantum physics of black holes. The authors find new results which shed light on microscopic nature of the evaporation process. PubDate: 2017-07-17T03:30:29.028799-05: DOI: 10.1002/andp.201700078

Authors:H. Kurkjian; Y. Castin, A. Sinatra Abstract: We study the interactions among phonons and the phonon lifetime in a pair-condensed Fermi gas in the BEC-BCS crossover in the collisionless regime. To compute the phonon-phonon coupling amplitudes we use a microscopic model based on a generalized BCS Ansatz including moving pairs, which allows for a systematic expansion around the mean field BCS approximation of the ground state. We show that the quantum hydrodynamic expression of the amplitudes obtained by Landau and Khalatnikov apply only on the energy shell, that is for resonant processes that conserve energy. The microscopic model yields the same excitation spectrum as the Random Phase Approximation, with a linear (phononic) start and a concavity at low wave number that changes from upwards to downwards in the BEC-BCS crossover. When the concavity of the dispersion relation is upwards at low wave number, the leading damping mechanism at low temperature is the Beliaev-Landau process 2 phonons 1 phonon while, when the concavity is downwards, it is the Landau-Khalatnikov process 2 phonons 2 phonons. In both cases, by rescaling the wave vectors to absorb the dependence on the interaction strength, we obtain a universal formula for the damping rate. This universal formula corrects and extends the original analytic results of Landau and Khalatnikov [ZhETF 19, 637 (1949)] for the 22 processes in the downward concavity case. In the upward concavity case, for the Beliaev 1 2 process for the unitary gas at zero temperature, we calculate the damping rate of an excitation with wave number q including the first correction proportional to q7 to the q5 hydrodynamic prediction, which was never done before in a systematic way.Low temperature phonon damping rates in an unpolarised spin-1/2 superfluid Fermi gas are calculated in the collisionless regime for any interaction strength across the BEC-BCS crossover. Close to unitarity the leading damping mechanism changes from the three-phonon Beliaev-Landau to the yet unobserved four-phonon Landau-Khalatnikov damping. The 1949 Landau and Khalatnikov calculation is corrected and extended. At unitarity at zero temperature the first correction to the Beliaev damping rate is obtained. PubDate: 2017-07-13T06:31:45.629842-05: DOI: 10.1002/andp.201600352

Authors:A. F. Kemper; M. A. Sentef, B. Moritz, T. P. Devereaux, J. K. Freericks Abstract: We review recent work on the theory for pump/probe photoemission spectroscopy of electron-phonon mediated superconductors in both the normal and the superconducting states. We describe the formal developments that allow one to solve the Migdal-Eliashberg theory in nonequilibrium for an ultrashort laser pumping field, and explore the solutions which illustrate the relaxation as energy is transferred from electrons to phonons. We focus on exact results emanating from sum rules and approximate numerical results which describe rules of thumb for relaxation processes. In addition, in the superconducting state, we describe how Anderson-Higgs oscillations can be excited due to the nonlinear coupling with the electric field and describe mechanisms where pumping the system enhances superconductivity.This paper reviews work on nonequilibrum dynamical mean-field theory for superconductors emphasizing different phenomena that can be observed in photoemission. PubDate: 2017-07-13T05:52:53.539043-05: DOI: 10.1002/andp.201600235

Authors:Ferdinand Kisslinger; Matthias Popp, Johannes Jobst, Sam Shallcross, Heiko B. Weber Abstract: We present an overview of recent charge carrier transport experiments in both monolayer and bilayer graphene, with emphasis on the phenomena that appear in large-area samples. While many aspects of transport are based on quantum mechanical concepts, in the large-area limit classical corrections dominate and shape the magnetoresistance and the tunneling conductance. The discussed phenomena are very general and can, with little modification, be expected in any atomically thin 2D conductor.The authors present an overview of recent charge carrier transport experiments in both monolayer and bilayer graphene, with emphasis on the phenomena that appear in large-area samples. In the large-area limit classical corrections dominate and shape the magnetoresistance and the tunneling conductance. The discussed phenomena are very general and can, with little modification, be expected in any atomically thin 2D conductor. PubDate: 2017-07-13T05:52:23.636001-05: DOI: 10.1002/andp.201700048

Authors:J. R. M. Nova; F. Sols, I. Zapata Abstract: The outcoupling of a Bose-Einstein condensate through an optical lattice provides an interesting scenario to study quantum transport phenomena or the analog Hawking effect as the system can reach a quasi-stationary black-hole configuration. We devote this work to characterize the quantum transport properties of quasi-particles on top of this black-hole configuration by computing the corresponding scattering matrix. We find that most of the features can be understood in terms of the usual Schrödinger scattering. In particular, a transmission band appears in the spectrum, with the normal-normal transmission dominating over the anomalous-normal one. We show that this picture still holds in a realistic experimental situation where the actual Gaussian envelope of the optical lattice is considered. A peaked resonant structure is displayed near the upper end of the transmission band, which suggests that the proposed setup is a good candidate to provide a clear signal of spontaneous Hawking radiation.Due to its high quasi-stationarity, the analog black-hole resulting from the outcoupling of a condensate through an optical lattice is an optimal scenario for studying quantum transport phenomena, including the analog of Hawking radiation. This work presents a study of the associated quasi-particle spectrum. The Hawking spectrum shows a highly non-thermal behavior whenever the top of the conduction band is below the threshold frequency, which could ease its detection. PubDate: 2017-07-13T05:51:10.894926-05: DOI: 10.1002/andp.201600385

Authors:Yi-Hao Kang; Ye-Hong Chen, Bi-Hua Huang, Jie Song, Yan Xia Abstract: In this paper, a scheme is put forward to design pulses which drive a three-level system based on the reverse engineering with Lewis-Riesenfeld invariant theory. The scheme can be applied to a three-level system even when the rotating-wave approximation (RWA) can not be used. The amplitudes of pulses and the maximal values of detunings in the system could be easily controlled by adjusting control parameters. We analyze the dynamics of the system by an invariant operator, so additional couplings are unnecessary. Moreover, the approaches to avoid singularity of pulses are studied and several useful results are obtained. We hope the scheme could contribute to fast quantum information processing without RWA.The authors have proposed a scheme that design feasible pulses for fast manipulation of a three-level quantum system without using the the rotating-wave approximation. By analysis dynamics of the system via a new found Lewis-Riesenfeld invariant, the authors have given three approaches to design pulses, which could be smoothly turned on and turned off, and whose amplitudes could be easily controlled. Besides, no extra couplings are required in the scheme. PubDate: 2017-07-12T03:05:37.548632-05: DOI: 10.1002/andp.201700004

Authors:Adam Balcerzak; Mariusz P. Da̧browski, Vincenzo Salzano Abstract: We extend a new method to measure possible variation of the speed of light by using Baryon Acoustic Oscillations and the Hubble function onto an inhomogeneous pressure model of the universe. The method relies on the fact that there is a simple relation between the angular diameter distance (DA) maximum and the Hubble function (H) evaluated at the same maximum-condition redshift, which includes the speed of light c. One limit of such a method was the assumption of the vanishing of spatial curvature (though, as it has been shown, a non-zero curvature has negligible effect). In this paper, apart from taking into account an inhomogeneity, we consider non-zero spatial curvature and calculate an exact relation between DA and H. Our main result is the evaluation if current or future missions such as Square Kilometer Array (SKA) can be sensitive enough to detect any spatial variation of c which can in principle be related to the recently observed spatial variation of the fine structure constant (an effect known as α-dipole).The authors extend their method of cosmic rulers and cosmic clocks to check for spatial variations of the speed of light c. A specific model from the class of inhomogeneous Stephani cosmological models is proposed. It agrees with cosmological data from Type Ia Supernovae, Baryon Acoustic Oscillations, Cosmic Microwave Background, and Hubble parameter. The spatial variability of c has the merit of being falsifiable by SKA (Square Kilometer Array) mission. PubDate: 2017-07-12T03:05:23.313558-05: DOI: 10.1002/andp.201600409

Authors:Qi-Cheng Wu; Ye-Hong Chen, Bi-Hua Huang, Zhi-Cheng Shi, Jie Song, Yan Xia Abstract: In this paper, we propose a scheme to protect quantum state by utilizing the time-dependent decoherence-free subspaces (TDFSs) theory without the rotating-wave approximation (RWA). A coherent control is designed to drive the quantum system into the TDFSs, moreover, the singularities of the designed coherent control can be avoided by appropriately choosing the control parameters. From an experimental view point, the influences of variations of the control parameters and the imperfect initial state are discussed in detail. Numerical simulations confirm that the scheme can protect the quantum information from both the environmental decoherence and the control errors. In addition, by comparing with the scheme employing RWA, we show that the weak coherent control field is not suitable to create the TDFS, the counter-rotating terms in the strong coherent control are helpful to protect the quantum information.The work addresses a long-standing problem of protecting quantum system: when the rotating-wave approximation (RWA) breaks down, how can we protect the quantum information from both the environmental decoherence and the control errors by utilizing coherent control' The authors demonstrate the possibility to drive a two-level system without RWA protecting the purity of the quantum state in an environment that in principle induces decoherence. PubDate: 2017-07-12T01:35:36.033017-05: DOI: 10.1002/andp.201700186

Authors:Giulia Marcucci; Maria Chiara Braidotti, Silvia Gentilini, Claudio Conti Abstract: The description of irreversible phenomena is a still debated topic in quantum mechanics. Still nowadays, there is no clear procedure to distinguish the coupling with external baths from the intrinsic irreversibility in isolated systems. In 1928 Gamow introduced states with exponentially decaying observables not belonging to the conventional Hilbert space. These states are named Gamow vectors, and they belong to rigged Hilbert spaces. This review summarizes the contemporary approach using Gamow vectors and rigged Hilbert space formalism as foundations of a generalized “time asymmetric” quantum mechanics. We study the irreversible propagation of specific wave packets and show that the topic is surprisingly related to the problem of irreversibility of shock waves in classical nonlinear evolution. We specifically consider the applications in the field of nonlinear optics. We show that it is possible to emulate irreversible quantum mechanical process by the nonlinear evolution of a laser beam and we provide experimental tests by the generation of dispersive shock waves in highly nonlocal regimes. We demonstrate experimentally the quantization of decay rates predicted by the time-asymmetric quantum mechanics. This work furnishes support to the idea of intrinsically irreversible wave propagation, and to novel tests of the foundations of quantum mechanics.In 1928 Gamow introduced states with exponentiallydecaying observables belonging to a rigged Hilbert space: the Gamow vectors (GVs). In this review, the contemporary approach using GVs as foundations of the “time asymmetric” quantum mechanics, and its relation with the problem of irreversibility of shock waves in classical nonlinear evolution are shown. The optical dispersive wave breaking in highly nonlocal regimes emulates an irreversible quantum mechanical process, experimentally proved. PubDate: 2017-07-11T06:02:31.622134-05: DOI: 10.1002/andp.201600349

Authors:Shi-Tong Xu; Fu-Tai Hu, Meng Chen, Fei Fan, Sheng-Jiang Chang Abstract: Coupled dielectric-metal gratings are investigated for broadband terahertz (THz) wave polarization conversion and asymmetric transmission by the experiments and numerical simulations, which are composed of the subwavelength Si grating and metallic wire grating layers. The dielectric grating layer with a large artificial birefringence and low dispersion is employed as a phase engineered waveplate, and the metal wire grating arranged with a 45° angle to the dielectric grating is utilized as a high-efficiency polarizer. Due to the subwavelength integration, this coupled grating presents a local resonance coupling mechanism between dielectric and metal gratings, which greatly enhances the polarization rotation and expands the bandwidth, not a simple combination with dielectric and metallic gratings. The results demonstrate that a broadband asymmetric transmission with an extinction ratio of 30dB from 0.2 to 1.2 THz is achieved and the highest transmission of 90% can be obtained. It provides a simple way towards practical applications for THz artificial dispersion materials, polarization control and asymmetric transmission.Terahertz (THz) polarization converter has an irreplaceable role in manipulating the polarization states of the THz waves. Here, a coupled dielectric-metal grating is proposed for broadband THz wave polarization conversion and asymmetric transmission, which is composed of subwavelength Si deep relief grating and gold wire grating on the two surfaces of a Si substrate. The results show that a broadband asymmetric transmission is achieved with an extinction ratio of 30dB from 0.2 to 1.2 THz and the highest polarization conversion of 90% can be obtained. PubDate: 2017-07-11T06:01:58.289107-05: DOI: 10.1002/andp.201700151

Authors:Da Zhang; Yiqi Zhang, Zhaoyang Zhang, Noor Ahmed, Yanpeng Zhang, Fuli Li, Milivoj R. Belić, Min Xiao Abstract: We suggest a real physical system — the honeycomb lattice — as a possible realization of the fractional Schrödinger equation (FSE) system, through utilization of the Dirac-Weyl equation (DWE). The fractional Laplacian in FSE causes modulation of the dispersion relation of the system, which becomes linear in the limiting case. In the honeycomb lattice, the dispersion relation is already linear around the Dirac point, suggesting a possible connection with the FSE, since both models can be reduced to the one described by the DWE. Thus, we propagate Gaussian beams in three ways: according to FSE, honeycomb lattice around the Dirac point, and DWE, to discover universal behavior — the conical diffraction. However, if an additional potential is brought into the system, the similarity in behavior is broken, because the added potential serves as a perturbation that breaks the translational periodicity of honeycomb lattice and destroys Dirac cones in the dispersion relation.The fractional Schrödinger equation (FSE) is the fundamental equation of the fractional quantum mechanics. The fractional Laplacian in FSE causes a modulation of the dispersion relation of the system, which becomes linear in the limiting case. This change brings profound differences in the behavior of the wave function. Here, the authors compare the similarities between evolution described by FSE, evolution in honeycomb lattice described by usual Schrödinger equation, and find that the connection can be established via the Dirac-Weyl equation. PubDate: 2017-07-10T04:37:03.41991-05:0 DOI: 10.1002/andp.201700149

Authors:Yi-Hao Kang; Zhi-Cheng Shi, Bi-Hua Huang, Jie Song, Yan Xia Abstract: In this paper, we propose a protocol to achieve fast and robustness quantum information transfer (QIT) in annular and radial superconducting networks, where each quantum node is composed of a superconducting quantum interference device (SQUID) inside a coplanar waveguide resonator (CPWR). The process is based on reversely constructing time-dependent control Hamiltonian by designing evolution operator. With the protocol, the maximal population of lossy intermediate states and the amplitudes of pulses can be easily controlled by two corresponding control parameters. Therefore, one can design feasible pulses for QIT with great flexibility. Besides, the speed of the QIT here is much faster compared with that with adiabatic QIT. Moreover, numerical simulations show that the protocol still possesses high fidelity when lossy factors and imperfect operations are taken into account. Therefore, the protocol may provide a useful way to manipulate quantum information networks.The authors have proposed a protocol to achieve fast and robustness quantum information transfer (QIT) in annular and radial superconducting networks. Based on the method, which reversely constructs time-dependent control Hamiltonian by designing evolution operator, QIT in referenced superconducting networks are much faster than adiabatic QIT. Moreover, numerical simulations show that the protocol still possesses high fidelity when lossy factors and imperfect operations are taken into account. PubDate: 2017-07-10T04:36:53.597116-05: DOI: 10.1002/andp.201700154

Authors:Sergey D. Ganichev; Dieter Weiss, Jonathan Eroms Abstract: Terahertz field induced photocurrents in graphene were studied experimentally and by microscopic modeling. Currents were generated by cw and pulsed laser radiation in large area as well as small-size exfoliated graphene samples. We review general symmetry considerations leading to photocurrents depending on linear and circular polarized radiation and then present a number of situations where photocurrents were detected. Starting with the photon drag effect under oblique incidence, we proceed to the photogalvanic effect enhancement in the reststrahlen band of SiC and edge-generated currents in graphene. Ratchet effects were considered for in-plane magnetic fields and a structure inversion asymmetry as well as for graphene with non-symmetric patterned top gates. Lastly, we demonstrate that graphene can be used as a fast, broadband detector of terahertz radiation.The authors review experimental and theoretical studies of photocurrents driven by polarized terahertz radiation in graphene. The phenomenological and microscopic theory of various second order phenomena and the state-of-the-art of the experiments are discussed. They show that nonlinear transport opens up new opportunities for probing helical Dirac electron states, address prospectives of theoretical and experimental studies and discuss the application of structured graphene for fast room temperature detection of THz radiation. PubDate: 2017-07-07T05:56:31.378606-05: DOI: 10.1002/andp.201600406

Authors:Boris N. Narozhny; Igor V. Gornyi, Alexander D. Mirlin, Jörg Schmalian Abstract: The last few years have seen an explosion of interest in hydrodynamic effects in interacting electron systems in ultra-pure materials. In this paper we briefly review the recent advances, both theoretical and experimental, in the hydrodynamic approach to electronic transport in graphene, focusing on viscous phenomena, Coulomb drag, non-local transport measurements, and possibilities for observing nonlinear effects.The last few years have seen an explosion of interest in hydrodynamic effects in interacting electron systems in ultra-pure materials. This paper reviews the recent advances, both theoretical and experimental, in the hydrodynamic approach to electronic transport in graphene, focusing on viscous phenomena, Coulomb drag, non-local transport measurements, and possibilities for observing nonlinear effects. PubDate: 2017-07-07T04:21:36.423926-05: DOI: 10.1002/andp.201700043

Authors:Mehrdad Shaygan; Martin Otto, Abhay A. Sagade, Carlos A. Chavarin, Gerd Bacher, Wolfgang Mertin, Daniel Neumaier Abstract: The exploitation of the excellent intrinsic electronic properties of graphene for device applications is hampered by a large contact resistance between the metal and graphene. The formation of edge contacts rather than top contacts is one of the most promising solutions for realizing low ohmic contacts. In this paper the fabrication and characterization of edge contacts to large area CVD-grown monolayer graphene by means of optical lithography using CMOS compatible metals, i.e. Nickel and Aluminum is reported. Extraction of the contact resistance by Transfer Line Method (TLM) as well as the direct measurement using Kelvin Probe Force Microscopy demonstrates a very low width specific contact resistance down to 130 Ωμm. The contact resistance is found to be stable for annealing temperatures up to 150°C enabling further device processing. Using this contact scheme for edge contacts, a field effect transistor based on CVD graphene with a high transconductance of 0.63 mS/μm at 1 V bias voltage is fabricated.In this work, the authors report on the fabrication of edge contacts to large area CVD monolayer graphene using a CMOS compatible metal with a very low contact resistance. The improved contacting scheme enables the realization of high performance graphene devices. PubDate: 2017-07-05T12:32:35.88435-05:0 DOI: 10.1002/andp.201600410

Authors:M. Hilke; H. Eleuch Abstract: We evaluate the localization length of the wave (or Schrödinger) equation in the presence of a disordered speckle potential. This is relevant for experiments on cold atoms in optical speckle potentials. We focus on the limit of large disorder, where the Born approximation breaks down and derive an expression valid in the “quasi-metallic” phase at large disorder. This phase becomes strongly localized and the effective mobility edge disappears.The authors evaluate the localization length of the wave (or Schrödinger) equation in the presence of a disordered speckle potential. This is relevant for experiments on cold atoms in optical speckle potentials. The authors focus on the limit of large disorder, where the Born approximation breaks down and derive an expression based on a non-linear approximation valid in the “quasi-metallic” phase at large disorder. The picture shows an example of the amplitude (ln ψ ) of the wave solution as a function of position for a very strong speckle potential, which has several tunneling regions. PubDate: 2017-07-04T11:23:33.778577-05: DOI: 10.1002/andp.201600347

Authors:P. Willke; M. A. Schneider, M. Wenderoth Abstract: The continuous progress in device miniaturization demands a thorough understanding of the electron transport processes involved. The influence of defects - discontinuities in the perfect and translational invariant crystal lattice - plays a crucial role here. For graphene in particular, they limit the carrier mobility often demanded for applications by contributing additional sources of scattering to the sample. Due to its two-dimensional nature graphene serves as an ideal system to study electron transport in the presence of defects, because one-dimensional defects like steps, grain boundaries and interfaces are easy to characterize and have profound effects on the transport properties. While their contribution to the resistance of a sample can be extracted by carefully conducted transport experiments, scanning probe methods are excellent tools to study the influence of defects locally. In this letter, the authors review the results of scattering at local defects in graphene and other 2D systems by scanning tunneling potentiometry, 4-point-probe microscopy, Kelvin probe force microscopy and conventional transport measurements. Besides the comparison of the different defect resistances important for device fabrication, the underlying scattering mechanisms are discussed giving insight into the general physics of electron scattering at defects.In this review the recent research on local electron transport across extended, one-dimensional defects in graphene using scanning probe methods is summarized. In particular substrate steps, wrinkles, stacking faults, monolayer/bilayer-interfaces, collapsed wrinkles and grain boundaries are discussed. While these defects can have a significant influence on the total resistance of a sample they also help to shed light on the general physics of electron scattering at defects and the underlying scattering mechanisms. PubDate: 2017-07-04T11:22:50.881735-05: DOI: 10.1002/andp.201700003

Authors:Jürgen Kraus; Lena Böbel, Gregor Zwaschka, Sebastian Günther Abstract: Understanding and controlling the growth kinetics of graphene is a prerequisite to synthesize this highly wanted material by chemical vapor deposition on Cu, e.g. for the construction of ultra-stable electron transparent membranes. It is reviewed that Cu foils contain a considerable amount of carbon in the bulk which significantly exceeds the expected amount of thermally equilibrated dissolved carbon in Cu and that this carbon must be removed before any high quality graphene may be grown. Starting with such conditioned Cu foils, systematic studies of the graphene growth kinetics in a reactive CH4/H2 atmosphere allow to extract the following meaningful data: prediction of the equilibrium constant of the graphene formation reaction within a precision of a factor of two, the confirmation that the graphene growth proceeds from a C(ad)-phase on Cu which is in thermal equilibrium with the reactive gas phase, its apparent activation barrier and finally the prediction of the achievable growth velocity of the growing graphene flakes during chemical vapor deposition. As a result of the performed study, growth parameters are identified for the synthesis of high quality monolayer graphene with single crystalline domains of 100–1000 μm in diameter within a reasonable growth time.A systematic study of the graphene growth on carbon depleted Cu foils allows to understand the chemical vapor deposition kinetics and to predict the achievable growth velocity of graphene flakes. The experimentally determined thermal equilibrium constant of the reaction agrees with an approximation by thermodynamic data within a factor of two. The identified optimum of the growth parameters allows the growth of high quality graphene. PubDate: 2017-07-03T08:10:16.960401-05: DOI: 10.1002/andp.201700029

Authors:Nils Richter; Zongping Chen, Marie-Luise Braatz, Fabienne Musseau, Nils-Eike Weber, Akimitsu Narita, Klaus Müllen, Mathias Kläui Abstract: We present an overview of charge transport in selected one-, two- and three-dimensional carbon-based materials with exciting properties. The systems are atomically defined bottom-up synthesized graphene nanoribbons, doped graphene and turbostratic graphene micro-disks, where up to 100 graphene layers are rotationally stacked. For turbostratic graphene we show how this system lends itself to spintronic applications. This follows from the inner graphene layers where charge carriers are protected and thus highly mobile. Doped graphene and graphene nanoribbons offer the possibility to tailor the electronic properties of graphene either by introducing heteroatoms or by confining the system geometrically. Herein, we describe the most recent developments of charge transports in these carbon systems.This review describes the properties of carbon allotropes from 1D graphene nanoribbons to 2D doped graphene and 3D turbostratic graphene micro-disks. While turbostratic graphene lends itself to spintronic applications resulting from protected graphene layers, where charge carriers are highly mobile, doped graphene and graphene nanoribbons offer the possibility to tailor the electronic properties by introducing heteroatoms and using geometrical confinement. PubDate: 2017-07-03T08:09:39.470098-05: DOI: 10.1002/andp.201700051

Authors:Y. F. Chen; J. C. Tung, P. H. Tuan, K. F. Huang Abstract: In the three-dimensional (3D) transversely symmetric oscillator, there are plentiful degeneracies and gaps in the quantum energy spectrum as a function of the ratio of the transverse to longitudinal frequency. It is theoretically verified that while the SU(2) interaction destroys the original degeneracies, numerous new degeneracies and gaps emerge around the original degeneracies to form a similar fine energy spectrum. The classical trajectories at the emergent degeneracies are analyzed to be localized on the 3D parametric surfaces which are constituted by the topologically invariant curves in the transverse tomography. The quantum coherent states are exploited to develop the wave functions that correspond to the 3D geometric surfaces in classical dynamics. Furthermore, the wave structures of the stationary coherent states at small quantum numbers are explored and found to display peculiar patterns with symmetries related to classical trajectories.It is theoretically verified that while the SU(2) interaction destroys the original degeneracies in the three-dimensional (3D) transversely symmetric oscillator, numerous new degeneracies and gaps emerge around the original degeneracies to form a fine energy spectrum. The classical trajectories at the emergent degeneracies are localized on the 3D parametric surfaces which are constituted by the topologically invariant curves in the transverse tomography. The quantum coherent states are developed to obtain the wave functions for manifesting the correspondence with the 3D geometric surfaces in classical dynamics. The feature of the theoretical coherent states can be linked to the formation of the experimental 3D structured laser modes. PubDate: 2017-06-26T01:08:16.498495-05: DOI: 10.1002/andp.201600253

Authors:Konstantin G. Zloshchastiev Abstract: It is shown that quantum sustainability is a universal phenomenon which emerges during environment-assisted electronic excitation energy transfer (EET) in photobiological complexes (PBCs), such as photosynthetic reaction centers and centers of melanogenesis. We demonstrate that quantum photobiological systems must be sustainable for them to simultaneously endure continuous energy transfer and keep their internal structure from destruction or critical instability. These quantum effects occur due to the interaction of PBCs with their environment which can be described by means of the reduced density operator and effective non-Hermitian Hamiltonian (NH). Sustainable NH models of EET predict the coherence beats, followed by the decrease of coherence down to a small, yet non-zero value. This indicates that in sustainable PBCs, quantum effects survive on a much larger time scale than the energy relaxation of an exciton. We show that sustainable evolution significantly lowers the entropy of PBCs and improves the speed and capacity of EET.The work addresses a long-standing problem of quantum photobiology and UV-physiology: is there a universal mechanism, which would explain high efficiency and sustainability of energy transfer in otherwise completely different photobiological systems inside living organisms or organelles, such as photosynthetic reaction centers and centers of melanogenesis? It is shown that certain interactions of these systems with their environment facilitate energy transfer, preserve quantum coherence and reduce entropy. PubDate: 2017-03-30T06:20:46.923457-05: DOI: 10.1002/andp.201600185

Authors:Dario Bercioux; Omjyoti Dutta, Enrique Rico Abstract: We investigate the spectral properties of a quasi-one-dimensional lattice in two possible dimerisation configurations. Both configurations are characterised by the same lattice topology and the identical spectra containing a flat band at zero energy. We find that, one of the dimerised configuration has similar symmetry to a one-dimensional chain proposed by Su-Schrieffer-Heeger for studying solitons in conjugated polymers. Whereas, the other dimerised configuration only shows non-trivial topological properties in the presence of chiral-symmetry breaking adiabatic pumping.We study an enlarged version of the popular SSH model for studying solitons in polyacetylene. Our system allows for two possible dimerized phases. We show that one of the two is a higher dimensional representation of the SSH model, whereas the second one is a trivial representation that does not show any topological phase. PubDate: 2017-03-08T03:15:44.38263-05:0 DOI: 10.1002/andp.201600262