Journal of Low Temperature Physics最新文献

This study presents a computational investigation of the rotating effects on the thermomagnetic properties of a charged particle confined to a two-dimensional quantum ring with the Aharonov–Bohm flux and external magnetic field. To this end, we have considered the Schrödinger equation (SE) including the gauge field for the rotating process and the potential model of the electromagnetic field. By solving the SE, we have calculated the eigenvalues and eigenfunctions of the system. Using obtained eigenvalues, we have evaluated the partition function of the considered system and have deduced thermodynamic properties such as mean energy, specific heat in constant volume, entropy and free energy. Also, we have calculated magnetic properties of the system such as the magnetization and magnetic susceptibility of the charged particle. Our findings represents that the rotation has a significant effect on thermodynamic and magnetic properties of a 2D quantum ring.

In this paper, we studied the photon blockade (PB) effect within a fully coupled tripartite hybrid system, where a two-level atom is integrated into a cavity optomechanical system. By applying the Schrieffer–Wolff transformation, the tripartite problem is effectively converted into a bipartite problem. The resulting effective Hamiltonian features multi-adjustable parameters: the detunings among the atomic transition frequency, the cavity resonance frequency, the driving field frequency, and the driving amplitude. By means of the probability amplitude method and the quantum master equation method, we investigated the PB effects of the system under varying detunings and driving amplitude. Furthermore, the results show that the PB effect can be achieved within a broader detuning range when the driving amplitude increases. It is noteworthy that the two-level atom plays a non-negligible role in the PB effect because it induces a cavity frequency shift, thereby providing an additional adjustable parameter for the system to optimize the PB effect. Our findings hold instructive and practical value for the design and optimization of relevant experiments in the field of quantum optics.

Quantum droplets formed by rubidium, lithium, and sodium atoms have been analyzed in this paper by using a logarithmic-type Gross–Pitaevskii equation. Variational methods and numerical techniques were employed to solve the corresponding nonlinear equations. A disk-shaped Bose–Einstein condensate was analyzed to assess its radial evolution. Additionally, free expansion under rotation of the BEC was studied. Compression and expansion around the equilibrium radius were observed in different scenarios, predicting self-confinement, which implies the formation of quantum droplets originating from a BEC state. Briefly, the physical aspects of the system and the possible formation of Bose-nova effects are discussed.

The static magnetic properties of the silica-based aerogels of Cryogel® and Pyrogel®, manufactured by Aspen Aerogels®, were measured over a range of temperatures ((2,textrm{K} le T le 400,textrm{K})) and in magnetic fields up to 70 kG. These data and a model of the responses are reported, so these properties are familiar to others who may benefit from knowing them before the materials are employed in potential applications.

We have investigated how the low concentrations of ferromagnetic Co-nanoparticles in intergranular networks of multi-layered Y₃Ba₅Cu₈O_18-δ (Y358) superconductor affect the coherence length (ξ_c) at absolute zero temperature and critical current density, J_c, near the superconducting phase transition region. Fluctuation-induced conductivity (FIC) is used to extract ξ_c (0). An increasing trend of ξ_c (0) with increasing concentration of Co is observed, attributed to the deterioration of the superconducting properties. We have extracted J_c from current–voltage (IV) characteristics in the phase transition region. Reduction in J_c has also been observed with increasing the concentration of Co-nanoparticles.

We describe a newly developed top-loading ⁴He sorption refrigerator. The top-loading configuration allows for rapid sample exchange, efficient cooling, and modular probe construction. A prototype comprises a condenser, an evaporator, a charcoal adsorption pump, and a top-loading probe, precooled by a Gifford–McMahon cryocooler. The base temperature and hold time in single-shot mode are 0.95 K and 2.5 h, respectively. The prototype provides a useable cooling power of 1.85 mW at 1 K.

This study explores quantum information dynamics in asymmetrically coupled double quantum dots, analyzing the effects of symmetry, initial state, and Coulomb interactions on correlation preservation. Results show that symmetry enhances entanglement robustness, while asymmetry and high entanglement increase sensitivity to decoherence. Strong Coulomb interactions support fidelity and capacity retention. These insights are relevant for optimizing protocols such as dense coding and teleportation in decohering environments.

Superconducting cables with complex multi-stage helical structures are essential components of the superconducting magnet systems of the International Thermonuclear Experimental Reactor. These cables often experience contact issues that can adversely affect their conductive properties. This study introduces a three-dimensional numerical model designed to accurately analyze the contact characteristics of multi-stage superconducting cables subjected to tensile strain. The model begins by defining the multi-stage geometry of the cable, and then evaluates the distribution of contact pressures and contact regions across individual strands. The numerical model was validated through comparison with existing reference data. An average contact force is introduced to quantify the magnitude of contact force on each strand. The study analyzes the effects of variations in the helical pitches of each stage of the cable on contact characteristics, as well as the influence of changes in the helical pitches of lower-stage cables on the contact characteristics of higher-stage cables. This research enhances the understanding of contact characteristics in multi-stage superconducting cables and provides valuable insights for optimizing the design of advanced hierarchical helical structures.

CaMnO₃, a perovskite manganite known for its antiferromagnetic (AFM) and other physical properties, has underexplored transport properties and temperature coefficient of resistance (TCR). We report exceptional charge transport phenomena in orthorhombic CaMnO₃, revealing a record negative temperature coefficient of resistance (TCR =  − 31.8% K⁻¹ at 21 K) for antiferromagnetic insulators. Magnetic characterization shows a Néel temperature (T_N) of 81.5 K. This magnetic transition govern distinct charge transport regimes, variable-range hopping (VRH) below T_N and small polaron (SP) conduction above T_N, demonstrating the existence of magnetic-electric coupling. Remarkably, the material exhibits field-independent TCR stability up to 6 T and significant magnetoresistance (MR =  − 17.5% at 22 K). These findings demonstrate CaMnO₃ potential for antiferromagnetic spintronic applications, particularly in magnetic sensors and spin-engineered thermal detection technologies in extreme environments.

Helium sorption coolers are widely used for achieving sub-kelvin temperatures due to their advantages of no moving parts, simple structure, and high reliability. While research has primarily focused on system design and sorption characteristics, studies on the condensation process of helium gas in these coolers remain limited. In this study, a three-dimensional simulation model is developed based on a laboratory helium sorption cooler prototype using helium-4 (4He) as the working fluid. The cooler reaches a minimum temperature of 827 mK with a holding time of 20 h. Experimental validation confirms the high accuracy of the model. The study analyzes the flow dynamics of liquid helium during condensation. Liquid helium flows along the narrow walls of the condenser heat exchanger, enters the evaporator through the pump tube, and evaporates, lowering the evaporator temperature. The evaporated helium gas then rises through the center of the pump tube. The study also examines the effect of pre-cooling temperature and operating pressure on the cooling rate. A decrease in pre-cooling temperature from 3.3 to 3.2 K leads to a sharp increase in the cooling rate, with cooling time dropping from 167 to 123 s. As the pre-cooling temperature further drops, the cooling time continues to decrease, but the impact on the cooling rate diminishes. Similarly, increasing the operating pressure from 37 to 41 kPa accelerates the cooling process initially, but the impact lessens as pressure continues to rise.