Journal of Low Temperature Physics最新文献

In this study, we employed Density Functional Theory to explore the electronic structure and superconducting properties of pristine LiFeAs and 50% Ru-substituted LiFeAs ((hbox {LiFe}_{0.5}) (hbox {Ru}_{0.5})As). The calculations were performed using the Quantum ESPRESSO package with projector-augmented wave pseudopotentials and the Perdew–Burke–Ernzerhof exchange–correlation functional. Superconducting characteristics were evaluated within the framework of Density Functional Perturbation Theory, through which we determined the superconducting transition temperature ((hbox {T}_textrm{c})), electronic density of states, phonon dispersion relations, electron–phonon coupling constant ((lambda)), Eliashberg spectral function [(alpha {^{2}}F(omega ))], and the logarithmic average phonon frequency ((langle omega_{log } rangle)). The optimized lattice parameters were determined to be a = 3.34 (mathring{A}) and c = 5.32 (mathring{A}) for LiFeAs, and a = 3.50 (mathring{A}) and c = 5.43 (mathring{A}) for (hbox {LiFe}_{0.5}) (hbox {Ru}_{0.5})As, in good agreement with previously reported theoretical values. The phonon dispersion curves of both LiFeAs and LiFe_0.5Ru_0.5 As exhibit no imaginary frequencies, confirming their dynamical stability in this study. Nevertheless, the calculated superconducting transition temperatures ((hbox {T}_textrm{c})) at 0 kbar and 600 kbar were 0.639 K and 4.38 K, respectively, both significantly lower than experimental measurements. (hbox {Ru}_{0.5}) This discrepancy suggests that, beyond electron–phonon coupling, additional mechanisms particularly spin and orbital fluctuations likely play a significant role in driving superconductivity in Fe-based compounds.

A novel (H_{textrm{c2}}) suppression mechanism is theoretically proposed in a spin-triplet superconductor (SC) with equal spin pairs. We show that the upper critical field (H_{textrm{c2}}) can be reduced from the orbital depairing limit (H^{textrm{orb}}_{textrm{c2}}) to arbitrarily small value, keeping the second-order phase transition nature. This mechanism is sharply different from the known Pauli–Clogston limit for a spin-singlet SC where the reduction is limited to (sim)0.3(H^{textrm{orb}}_{textrm{c2}}) with the first-order transition when the Maki parameter goes infinity. This novel (H_{textrm{c2}}) suppression mechanism is applied to (hbox {UTe}_2), which is a prime candidate for a spin-triplet SC, to successfully analyze the (H_{textrm{c2}}) data for various crystalline orientations both under ambient and applied pressure, and to identify the pairing symmetry. It is concluded that the non-unitary spin-triplet state with equal spin pairs is realized in (hbox {UTe}_2), namely (({hat{b}}+i{hat{c}})k_a) in (^3hbox {B}_{textrm{3u}}) which is classified under finite spin–orbit coupling scheme.

In this study, the effect of 1 mol% hexylbenzene doping on the structural, thermal, and magnetic properties of MgB₂/Fe superconducting wires was investigated. Differential scanning calorimetry (DSC) showed that the additive reduced the MgB₂ formation temperature, while X-ray diffraction (XRD) analysis indicated decreased crystallite size (from 51.6 to 39.9 nm) and increased microstress. The superconducting transition temperature (T_c) decreased slightly from 38.6 K to 38.2 K, accompanied by a broader transition. The critical current density (J_c) of the doped sample was one order of magnitude lower, with values of ~ 10⁵ A/cm² at 5 K (self-field) in the pure wire compared to ~ 10⁴ A/cm² in the doped one. Flux pinning analysis revealed that the normalized pinning force (F_p/F_p,max) shifted to lower fields and weakened after doping, confirming the degradation of pinning efficiency. These results demonstrate that while hexylbenzene facilitates MgB₂ phase formation, it negatively affects the superconducting performance of MgB₂/Fe wires.

The present work examines magnetization plateaus in bilayer pentagraphene-like nanostructures by Monte Carlo techniques. The result reveals a sequence of distinct magnetization plateaus influenced by the balance between exchange interactions, the applied crystal field, and thermal fluctuations. These results highlight how subtle changes in system parameters can drive complex magnetic behavior, contributing to a deeper understanding of nanoscale magnetism and aiding in the development of advanced 2D magnetic devices.

We study the dynamics of solitons in a driven-dissipative exciton–polariton superfluid; by employing a perturbed variational approximation, we get a set of ordinary differential equations to describe the dynamics of solitons. A spontaneously walking soliton is found in this driven-dissipative superfluid, and the soliton position exhibits a unidirectional motion. We mainly discuss how the pumping strength F and decay rate (gamma) influence the solitons dynamics. Meanwhile, the stability properties of the corresponding solitons are also investigated on the P(V) criterion, with P and V being the momentum and the velocity of the solitons.

Neutrinoless double-beta decay (0(nu beta beta)) experiments constitute a pivotal probe for elucidating the characteristics of neutrinos and further discovering new physics. Compared to the neutron transmutation-doped germanium thermistors used in 0(nu beta beta) experiments such as CUORE, transition edge sensors (TESs) theoretically have a relatively faster response time and higher energy resolution. These make TES detectors good choice for next generation 0(nu beta beta) experiments. In this paper, AlMn alloy superconducting films, the main components of TES, were prepared and studied. The relationship between critical temperature ((T_{text{c}})) and annealing temperature was established, and the impact of magnetic field on (T_{text{c}}) was tested. The experimental results demonstrate that the (T_{text{c}}) of AlMn film can be tuned in the required range of 10–20 mK by using the above methods, which is a key step for the application of AlMn TES in 0(nu beta beta) experiment. In the test range, the (T_{text{c}}) of AlMn film is sensitive to out-of-plane magnetic field but not to the in-plane magnetic field. Furthermore, we find that a higher annealing temperature results in a more uniform distribution of Mn ions in depth, which opens a new avenue for elucidating the underlying mechanism for tuning (T_{text{c}}).

Sorption coolers show strong potential for ground-based physical experiments and space exploration in the sub-Kelvin temperature regime, with their performance critically dependent on the adsorption behavior of helium on selected adsorbents. While most previous studies have focused on activated carbon, the present work systematically investigates the helium adsorption behavior of three porous materials: metal–organic framework (MOF) HKUST-1, single-walled carbon nanotubes (SWCNT), and multilayer graphene (MLG), over a temperature range of 4 to 77 K and a pressure range of 1 to 500 kPa. Evaluation of several adsorption isotherm models indicates that the Brunauer–Emmett–Teller (BET) model most accurately captures adsorption characteristics of three materials. Experimental results reveal a pronounced temperature dependence. In the low-temperature domain (4 to 10 K), adsorption capacity increases sharply with pressure; however, in the higher-temperature domain (20 K and above), adsorption tends toward saturation. Moreover, the relative adsorption performance of the three materials varies significantly with both temperature and pressure. Under low-temperature, low-pressure conditions (1 kPa, 4 K), SWCNT exhibit the highest adsorption capacity (24.03 mmol g^-1), making them particularly well suited for low-pressure refrigeration applications. In contrast, MLG shows the most significant enhancement in adsorption at high pressures: at 6 K, its isotherm exhibits a pronounced increase with pressure, indicating strong affinity for helium under high-pressure conditions. HKUST-1, by comparison, exhibits a lower overall adsorption capacity, likely due to limitations associated with its framework stability and pore occupancy behavior. These findings provide an experimental basis and theoretical support for the selection and optimization of adsorbents in low-temperature adsorption refrigeration systems.

The magnetization process of the (S=2) antiferromagnetic chain with two competing anisotropies is investigated using the numerical diagonalization of finite-size clusters and some size scaling analyses. As a result, it is found that the system possibly exhibits the translational symmetry broken magnetization plateaus at 1/4 and 3/4 of the saturation magnetization, as well as at 1/2. The phase diagrams for the anisotropies at 1/4, 3/4 and 1/2 magnetizations are presented. In addition, the magnetization curves for several typical anisotropy parameters are obtained.

The flow measurement of cryogenic fluids is frequently complicated by physical phenomena such as phase transition and cavitation, which can significantly impair measurement accuracy and system stability. Multi-stage perforated plate flowmeters have attracted increasing attention due to their potential for accurate flow measurement. However, most existing studies have focused on performance under non-cryogenic conditions, while the unique flow behavior exhibited by cryogenic fluids is often overlooked. In this study, a numerical approach is employed to investigate the flow characteristics of cryogenic fluids through double-stage perforated plate structures. A systematic evaluation is conducted to assess the influence of various operating conditions and structural features on physical flow properties, key dimensionless measurement parameter configurations, and cavitation-induced thermal effects, including the pressure loss coefficient, discharge coefficient, and temperature drop coefficient. The results indicate that when the spacing between plates exceeds a certain threshold, the variations in these parameters tend to stabilize. Furthermore, a novel asymmetric double-stage perforated plate design is proposed. Compared to the symmetric structure, the pressure loss coefficient and discharge coefficient improved by 26.9% and 29.6%, respectively, while the temperature drop coefficient decreased by approximately 30.6%. This suggests that the asymmetric structure can enhance flow measurement accuracy and stability by trading off energy loss. These findings can reveal the underlying mechanisms by which plate geometry influences flow characteristics and measurement accuracy, thereby offering valuable theoretical guidance for the high-precision measurement of cryogenic fluids.

AlMn alloy films are widely fabricated into superconducting transition edge sensors (TESs) for the detection of cosmic microwave background radiation. However, the application in X-ray or gamma-ray detection based on AlMn TES is rarely reported. In this study, X-ray TES detectors based on unique annular AlMn films are developed. The fabrication processes of TES detectors are introduced in detail. The characteristics of three TES samples are evaluated in a dilution refrigerator. The results demonstrate that the I-V characteristics of the three annular TES detectors are highly consistent. The TES detector with the smallest absorber achieved the best energy resolution of 11.0 eV @ 5.9 keV, which is inferior to the theoretical value. The discrepancy is mainly attributed to the larger readout electronics noise than expected.