Journal of Low Temperature Physics最新文献

The performance of the micro thermoacoustic refrigerator under the condition of weak gas degeneracy is studied, and a new analysis model for an irreversible quantum thermoacoustic refrigerator is established in this paper. Based on quantum statistics and thermodynamics theory, some important performance parameters of the thermoacoustic refrigerator such as the dimensionless cooling rate and the Coefficient of Performance (COP) are derived with the new model. Through numerical examples, the method to optimize the performance by adjusting some operation or structure parameters is given. At the same time, a new method to select the length of the regenerator is also found.

In this work, we investigate the magnetic, magnetocaloric, and hysteresis properties of the Spin-2 Blume–Capel model with second nearest neighbor interaction, which is a good candidate for exploring the magnetic properties of the compound LaMnO₃, within the mean-field approximation. The Hamiltonian considered includes exchange interactions between first and second neighbors ((J_1) and (J_2)), the crystal field D, and an external magnetic field h. Phase diagrams reveal the presence of a tricritical point separating first- and second-order transitions. The magnetization shows a second-order transition in the absence of the external magnetic field and a transition to a superparamagnetic phase for (h/J_{2} ne 0). The magnetic entropy (-Delta S_m) increases with field strength, reaching a maximum of 0.272 for (h/J_2 = 5), while the relative cooling power (RCP) increases linearly. Finally, the system exhibits complex hysteresis behavior, with one, three, or four loops depending on the physical parameters considered. These results highlight the potential of the compound (hbox {LaMnO}_3) for magnetic refrigeration applications.

Faraday rotation of Weyl fermions under uniaxial strain has been investigated in which the tight-binding Hamiltonian and Kubo approach have been employed. The influence of the strain has been considered as a change of hopping parameter. Results show that the Faraday rotation angle can be controlled by the external strain. Meanwhile, results show that the sign of the Faraday rotation can be reversed at some ranges of strain and incident light frequency.

The behavior of the thermodynamic compressibility of a trapped ultracold Fermi gas at unitarity is explored as the temperature approaches the critical temperature and the gas undergoes a phase transition to a superfluid state. This phase transition offers an opportunity to probe the microscopic underpinnings of this transition and can serve as a test of theoretical approaches. In this study, the collective behavior of the gas as it undergoes this phase transition is described using normal modes. The Pauli principle is applied “on paper” using specific normal mode assignments that are consistent with this fundamental principle. This study finds a small signature of the transition at the critical temperature in contrast to previous experimental and theoretical results.

In the process of 25% K and 12.5% P-doped BaFe₂As₂, the decrease of Fe ions height is accompanied by the suppression of antiferromagnetic order. Both K and P-doping cause an increase in the distance between Fe–As layers and a contraction of Fe–As bonds, and the contraction of Fe–As bond seems to be one of the most sensitive factors affecting antiferromagnetic suppression. It is found that the contraction of Fe–As bonds tends to be coordinated with an increase in Fe–Fe average distance to ultimately suppress antiferromagnetism to a smaller value. Similar structural changes result in K/P-doping causing Lifshitz transition (LT) and electronic topological transition (ETT). At the Fermi level, K-doping increases the density of states of Fe 3d and As 4p, while P-doping reduces these values.

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.