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Journal of Low Temperature Physics
Journal Prestige (SJR): 0.471  Citation Impact (citeScore): 1 Number of Followers: 7  Hybrid journal (It can contain Open Access articles)ISSN (Print) 1573-7357 - ISSN (Online) 0022-2291 Published by Springer-Verlag  [2468 journals]
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- Effects of Conical Geometry on Approximate Solutions Under Modified
Pöschl-Teller Potential and Shannon Entropy-
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Abstract: In this study, we investigate the behavior of non-relativistic quantum particles interacting with a modified Pöschl-Teller potential in the backdrop of a topological defect created by global monopoles. We derive the radial equation of the Schrödinger wave equation through a wave function ansatz and obtain an approximate $$\ell \ne 0$$-state eigenvalue solution by employing the Nikiforov-Uvarov method. Our analysis demonstrates that the presence of a global monopole affects both the energy eigenvalue and the wave functions of non-relativistic quantum particles, deviating from the behavior observed in flat space with this potential. Furthermore, we calculate the Shannon entropy for this quantum system and evaluate how the existence of the topological defect and potential influences it.
PubDate: 2025-04-04
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- Surface Electrons on Solid Quantum Substrates: A Brief Review
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Abstract: In this work an overview is given on experiments with surface electrons above the quantum solids hydrogen and neon. While two-dimensional ensembles of surface electrons on the quantum liquid superfluid helium have been studied already in great detail, investigations of electrons on quantum solids are rather sparse. Since recently electron-on-neon qubits have been shown to exhibit very long coherence times, there is a demand for understanding the conditions for a successful growth of thin solid neon films as a qubit substrate. Therefore, in this review also the triple point wetting phenomenon of the hydrogen isotopes and neon is discussed, which dominates the growth of solid films of these materials.
PubDate: 2025-04-03
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- Influence of Fe/Mo Stoichiometry on Structural and Magnetic Properties in
$$\hbox {Sr}_2\hbox {Fe}_x\hbox {Mo}_{2-x}\hbox {O}_6$$: A Theoretical and
Experimental Study-
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Abstract: The influence of nonstoichiometry on the structural and magnetic properties of $$\hbox {Sr}_2\hbox {FeMoO}_6$$ (SFMO) has been investigated by varying the ratio of Fe in polycrystalline samples. We demonstrate that changes in the Fe/Mo ratio can elevate the Curie temperature ($$T_\textrm{C}$$) in SFMO, even though the total magnetic moment is reduced at the same time. The discoveries of the stoichiometric imbalance between the cations Fe and Mo are discussed in the context of first-principles calculations on the electronic and magnetic structures of SFMO using the GGA+U method. Our theoretical results reveal that Fe deficiency reduces the $$T_\textrm{C}$$ due to the antiparallel alignment of Fe moments in Mo positions, which is consistent with experimental observations. In contrast, accurate $$T_\textrm{C}$$ trends for Fe excess are reproduced only by considering spin disorder, with both parallel and antiparallel Fe moment orientations. These insights provide a detailed understanding of the magnetic interactions in SFMO. Our findings lay the groundwork for developing innovative SFMO-based materials and emphasize the significance of stoichiometry control in optimizing SFMO properties.
PubDate: 2025-04-02
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- Investigation on the Mechanism of Maximum Efficiency Point for
Helium-Based Oscillating Heat Pipe-
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Abstract: Liquid helium cryogenic system is crucial for achieving low-temperature superconductivity in particle accelerator and controllable nuclear fusion devices. However, the heat conductivity of copper in the 4K region is 400–800 W m−1 K−1, which limits the performance of superconductivity system. The application of helium-based oscillating heat pipe (OHP) promotes this deficiency mitigation, with a maximum effective thermal conductivity (ETC) ranging from 4000 to 16,000 W m−1 K−1. Although numerous scholars have experimentally observed the maximum efficiency point of OHP, but its underlying mechanism remains unclear. In this study, a test rig for measuring the heat transfer performance and dynamic parameters of helium-based OHP in the 4K region was constructed. A numerical simulation method for the gas–liquid two-phase unsteady flow process in the OHP was established. The amplitude and period distribution of dynamic pressure fluctuations in OHP were analyzed. The correlation between its pressure fluctuations and heat transfer process was explored. Finally, the mechanism of the maximum efficiency point was revealed with the oscillating characteristics for helium-based OHP in the 4K region.
PubDate: 2025-04-02
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- A SFQ-to-CMOS Interface Circuit Based on SiGe BiCMOS for Josephson-CMOS
Hybrid System-
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Abstract: In this article, a novel DC-biased interface for multi-channel superconducting computers was designed, fabricated, and tested. Conventional interfaces for Josephson-CMOS memory rely on Josephson latching drivers (JLDs) or SQUID (Superconducting Quantum Interference Device) stacks to convert weak signals. However, SQUID stacks achieve high frequencies (tens of GHz) but produce only a few millivolts of output and occupy large areas, while JLDs provide higher output voltages (tens of millivolts) but require AC bias. To address these limitations, an interface based on SiGe BiCMOS (Silicon-Germanium Bipolar CMOS) technology was proposed, integrating the functions of JLDs and CMOS amplifiers into a single chip. Fabricated using a 130 nm SiGe BiCMOS process, the interface converts 200 µV to 1.2 V with a power consumption of only 386 µW per channel at 4.2 K. Low-frequency measurements demonstrated 21-channel signal conversion without the need for clock synchronization or additional amplifiers, significantly simplifying the cryogenic system. The proposed interface features key advantages, including DC bias, high gain, and asynchronous operation, making it a practical solution for superconductor–semiconductor signal conversion. While its maximum speed is currently limited, this interface represents a promising step toward scalable, energy-efficient multi-channel superconducting computers.
PubDate: 2025-04-01
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- Growth of Uniform Helium Submonolayers Adsorbed on Single-Surface Graphite
Observed by Surface X-ray Diffraction-
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Abstract: We observed surface X-ray diffraction from 4He submonolayers adsorbed on a single-surface graphite using synchrotron X-rays. Time evolutions of scattering intensities along the crystal truncation rod (CTR) were observed even after reaching the base low temperature in a selected condition of sample preparation. Our simulations for CTR scatterings based on the random double-layer model, in which helium atoms are distributed randomly in the first and second layers with a certain occupancy ratio, can consistently explain the observed intensity changes. These results support the scenario that He atoms are stratified initially as a nonequilibrium state and then relaxed into a uniform monolayer by surface diffusion, where the relaxation process was observed as a decrease in CTR scattering intensity. The observed time constant was, however, much longer than those estimated from quantum and thermal surface diffusions. This implies homogeneous processes in surface diffusions were strongly suppressed by local potentials in such as atomic steps or microcrystalline boundaries.
PubDate: 2025-03-27
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- Studies of Hydrogen Atom Recombination in Solid Hydrogen Deuteride
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Abstract: We used the method of electron spin resonance (ESR) to investigate the temperature-dependent recombination rate of H atoms in solid molecular hydrogen deuteride (HD). A 1.5 $$\mu$$m thick solid molecular HD film was deposited at a rate of 2 monolayer/s, onto a gold surface maintained at T=1.5 K. H and D atoms were accumulated in the film by maintaining radio-frequency electric discharge above the film for 19 days. After further storage of the sample for 48 h, at T < 1 K, the D atom signal vanished. The concentration of H atoms was monitored as the sample was warmed stepwise from 1.1 K to 2.8 K. The recombination rate of H atoms in solid HD was found to be proportional to temperature in this range.
PubDate: 2025-03-25
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- Structure of a Single-Quantum Vortex in 3He-A
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Abstract: We have performed numerical calculations of the structure of the single-quantum vortex in superfluid $$^3$$He-A. The GPU-accelerated large-scale numerical simulation is performed in the Ginzburg-Landau model and resolves length scales of both coherence-length-sized hard core and dipolar-length-sized soft core of the vortex. The calculations support previously suggested qualitative structure of the vortex, recently named as eccentric fractional skyrmion, and provide numerical values for the vortex energy, sizes and locations of the hard and soft cores and highly-asymmetric flow profile of the vortex.
PubDate: 2025-03-18
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- Correction: Benefits of the Use of Monte Carlo Simulations in Cryogenic
Detector Design-
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PubDate: 2025-03-15
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- Revisiting the properties of superfluid and normal liquid 4He using ab
initio potentials-
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Abstract: We investigate the properties of liquid $$^4$$He in both the normal and superfluid phases using path-integral Monte Carlo simulations and recently developed ab initio potentials that incorporate pair, three-body, and four-body interactions. By focusing on the energy per particle as a representative observable, we use a perturbative approach to quantify the individual contributions of the many-body potentials and systematically propagate their associated uncertainties. Our findings indicate that the three-body and four-body potentials contribute to the total energy by approximately 4% and 0.5%, respectively. However, the primary limitation in achieving highly accurate first principles calculations arises from the uncertainty in the four-body potential, which currently dominates the propagated uncertainty. In addition to the energy per particle, we analyze other key observables, including the superfluid fraction, condensed fraction, and pair distribution function, all of which demonstrate excellent agreement with experimental measurements.
PubDate: 2025-03-15
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- Nambu-Goldstone Modes in Two Segregated Bose-Einstein Condensates Limited
by a Hard Wall-
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Abstract: In the framework of the Gross-Pitaevskii theory, based on the double-parabola approximation method, we successfully found the expressions for dispersion relations of three NG modes of two immiscible Bose-Einstein condensates restricted by a hard wall (two phonons and a ripplon). For the first condensate component, which is not confined by a hard wall, we found one phonon and one ripplon. Meanwhile, for the second component confined by a hard wall, we found only one phonon (the dispersion relation depends on the position of the hard wall), and this manifests explicitly the finite-size effect.
PubDate: 2025-03-12
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- Some Thermomechanical Properties of an FCC Helium Cryocrystal
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Abstract: The paper presents analytic expressions of the Helmholtz free energy, the crystal parameters, the nearest neighbor distance between two atoms, the isothermal compressibility, the thermal expansion coefficient, the heat capacity at constant volume, the Gruneisen parameter, the isothermal elastic modulus, the Young modulus, the mean squared displacement and the Debye–Waller factor for FCC monoatomic crystal builded by the statistical moment method. The paper performs numerical calculation of the obtained theoretical results for FCC quantum crystals 3He and 4He using the Lennard–Jones (6–12) pair interaction potential and the coordination sphere method. Some calculated results are compared with the experimental data and other calculations.
PubDate: 2025-03-06
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- Density of States of the Hubbard Model Supplemented with the Quantizing
Magnetic Field-
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Abstract: Using the strong coupling diagram technique, we calculate the zero-temperature density of states $$\rho$$ of electrons on a square lattice immersed in a perpendicular uniform magnetic field. The electrons are described by Hubbard Hamiltonian. For moderate doping, Landau subbands are observed for small Hubbard repulsions U only. For larger U, the subbands are blurred. Instead, small peaks varying with the field induction B arise by opening the Mott gap in its vicinity. The related variation of $$\rho$$ with 1/B may be connected with the low-frequency quantum oscillations in lightly doped cuprates. For all considered repulsions, $$\rho$$ has gaps near transfer frequencies of the Hubbard atom, $$-\mu$$ and $$U-\mu$$, with $$\mu$$ the chemical potential. In the heavily underdoped case $$\mu
PubDate: 2025-03-05
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- Insights into Magnetic Properties of an Ising Nanoisland with Four-Spin
and Next-Nearest Neighbor Interactions-
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Abstract: We propose a multi-spin Ising model to report a computational study of a mixed spin-1 and spin-1/2 ferrimagnetic nanoisland. Employing the finite cluster approximation (FCA), we thoroughly examine how the four-spin interaction, next-nearest neighbor interaction, and crystal field affect the phase diagrams and the magnetic properties including magnetizations, internal energy, and specific heat. The exact calculations derived from the Hamiltonian at the ground state (T = 0) reveal the existence of a critical equation, J′ + J4 = − 4Js delimiting two distinct ground states (I) and (II). Phase diagrams analysis shows that the transition temperature Tc trends toward a tricritical point as the four-spin interaction J4 varies, without evidence of compensation phenomena; while the next-nearest neighbor interaction J' leads to the manifestation of compensation points only if J′ surpasses a Js-dependent threshold value. Interestingly, when the crystal field DS is inserted, one, two, or three compensation points may emerge according to the strength of J′.
PubDate: 2025-03-05
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- Evolution of Vortex Filaments and Reconnections in the Gross–Pitaevskii
Equation and its Approximation by the Binormal Flow Equation-
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Abstract: The evolution of a vortex line following the binormal flow equation (i.e. with a velocity proportional to the local curvature in the direction of the binormal vector) has been postulated as an approximation for the evolution of vortex filaments in both the Euler system for inviscid incompressible fluids and the Gross–Pitaevskii equation in superfluids. We address the issue of whether this is a suitable approximation or not and its degree of validity by using rigorous mathematical methods and direct numerical simulations. More specifically, we show that as the vortex core thickness goes to zero, the vortex core moves (at leading order and for long periods of time) with a velocity proportional to its local curvature and the binormal vector to the curve. The main idea of our analysis lies in a reformulation of the Gross–Pitaevskii equation in terms of associated velocity and vorticity fields that resemble the Euler system written in terms of vorticity in its weak form. We also present full numerical simulations aimed to compare Gross–Pitaevskii and binormal flow in various physical situations of interest such as the periodic evolution of deformed vortex rings and the reconnection of vortex filaments.
PubDate: 2025-02-21
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- The Cryogenic System of the MISTRAL Instrument: Design and In-lab
Performance-
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Abstract: We describe the design and performance of the cryostat and the multi-stage sub-K single-shot sorption cooler for the MIllimeter Sardinia Radio Telescope Receiver based on Array of Lumped elements kids (MISTRAL) experiment. MISTRAL is a W-band (77 - 103 GHz) Ti/Al bi-layer Lumped Elements Kinetic Inductance Detectors (LEKIDs) camera working at the Gregorian focus of the 64 m aperture Sardinia Radio Telescope (SRT), located in Sardinia (Italy). The cryogenic system, based on a 1.5 W at 4.2 K Pulse Tube (PT) cryocooler, provides the 4 K base temperature for the sub-K refrigerator, and cools down the cold optics and the filters chain of the instrument. The sub-K sorption cooler consists of two intermediate stages, $$^{4}$$He and $$^{3}$$He sorption refrigerators that allow to reduce the heat load on the ultra-cold head, and a twin stage of $$^{3}$$He sorption refrigerator providing the 0.2 K operation temperature for the 415-pixel array of LEKIDs. MISTRAL experiment was installed at SRT in May 2023, the technical commissioning started in June 2023. We will show the performance of the system in the laboratory.
PubDate: 2025-02-13
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- A Low Background Setup for Low Energy X-ray Detection in the Context of
the BabyIAXO/IAXO Axion Searches-
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Abstract: In the context of axion search in the BabyIAXO and IAXO helioscopes, various types of cryogenic detectors are investigated as high energy resolution, low energy threshold alternatives for the standard micromegas X-ray detectors. The setup presented in this paper comprising metallic magnetic calorimeter (MMC) X-ray detectors, a cryogenic local muon veto read out by an MMC, and internal and external lead shields, aims at establishing the background level that can be reached with MMCs in an above-ground experimental site. The low background setup is described in detail, and first observations from a low-temperature run are presented.
PubDate: 2025-02-11
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- Study of the T-Linear Resistivity in the Strange Metal Phase of the
Hole-Doped Cuprate Superconductors-
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Abstract: The low-temperature T-linear resistivity is a generic feature in the strange metal phase of overdoped cuprate superconductors; however, its origin is still not well understood. Based on the t–J model and the full charge-spin recombination scheme, the temperature dependence of electrical resistivity in the strange metal phase of the optimally doped and overdoped cuprates is studied. It is shown that at the optimal doping, the resistivity develops a linear-in-temperature behavior, while in the overdoped regime, the resistivity exhibits a nonlinear behavior which contains T-linear and T-quadratic components. The T-linear resistivity is thought to be dominated by isotropic inelastic scattering in the nodal region of the Fermi surface, where the most quasiparticle spectrum weight is assembled at around the tips of Fermi arcs.
PubDate: 2025-02-10
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- Aluminum Goalpost Nano-mechanical Devices at Low Temperatures
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Abstract: Mechanical objects have been widely used at low temperatures for decades, for various applications; from quantum fluids sensing with vibrating wires or tuning forks, to torsional oscillators for the study of mechanical properties of glasses, and finally micro and nano-mechanical objects with the advent of clean room technologies. These small structures opened up new possibilities to experimentalists, thanks to their small size. We report on the characterization of purely metallic goalpost nano-mechanical structures, which are employed today for both quantum fluids studies (especially quantum turbulence in $$^4$$He, $$^3$$He) and intrinsic friction studies (Two-level-systems unraveling). Extending existing literature, we demonstrate the analytic modeling of the resonances, in good agreement with numerical simulations, for both first and second mechanical modes. Especially, the impact of the curvature of the whole structure (and therefore, in-built surface stress) is analyzed, together with nonlinear properties. We demonstrate that these are of geometrical origin and device-dependent. Motion and forces are expressed in meters and Newtons experienced at the level of the goalpost’s paddle, for any magnitude or curvature, which is of particular importance for quantum fluids and solids studies.
PubDate: 2025-02-08
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- Magnetic and Magnetocaloric Effects and Phase Transition Critical Behavior
of Dy-Doped La0.7Ca0.3MnO3-
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Abstract: In this study, polycrystalline samples of La0.7Ca0.3-xDyxMnO3 (x = 0, 0.15) were synthesized via the solid-state reaction method. Their structures, magnetic properties, magnetocaloric effects, and critical behaviors associated with phase transitions were systematically investigated. All samples exhibited structures belonging to the Pbnm space group, characterized by precise compositions and good single-phase. The samples underwent paramagnetic-ferromagnetic (PM-FM) phase transitions at Curie temperatures (TC) of approximately 244 K for x = 0 and 132 K for x = 0.15. The incorporation of Dy significantly broadened the half height wide temperature range (ΔTFWHM) from 39.36 K (x = 0) to 121.92 K (x = 0.15). Consequently, the relative cooling capacity (RCP) of the samples was markedly increased, rising from 369.76 J·kg−1 (x = 0) to 721.09 J·kg−1 (x = 0.15). Furthermore, upon doping with x = 0.15, the phase transition type shifted from the first-order phase transition (FOPT) of the parent phase to a second-order phase transition (SOPT). This shift is attributed to the substitution of some Ca2+ ions by Dy3+, which weakened the double-exchange interaction and altered the phase transition type. Analysis of the critical behavior using the Kouvel-Fisher (K-F) and Modified Arrott plot (MAP) methods revealed that the critical features of the phase transition in La0.7Ca0.15Dy0.15MnO3 are better described by a Mean-Field Model with long-range ordering. Therefore, this study not only enriches our understanding of the physical properties of this class of materials but also enhances their potential for magnetic refrigeration (MR) applications.
PubDate: 2025-02-07
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