Journal of Low Temperature Physics最新文献

Recent researches on tilted Dirac cone materials have revealed an remarkable property; the spacetime metric can be altered in these materials by applying a perpendicular electric field. This phenomenon emerges near the Fermi velocity, which is significantly lower than the speed of light. According to this property, we derive the Ginzburg–Landau action from the microscopic BCS Hamiltonian for tilted Dirac cone materials. The derivation is performed near the superconductivity critical point within the framework of Dirac cone spacetime. The novelty of the present work lies in deriving a generalized Ginzburg–Landau action that explicitly depends on the spacetime metric, where the metric is tuned by an external electric field. This framework also enables the extension of the Ginzburg–Landau theory to higher temperatures, though subject to certain limitations.

We study the localization properties of the quasiperiodic one-dimensional helical chain with two tunneling paths: nearest-neighbor and a long-range hop that connects sites of consecutive helical turns. Using exact diagonalization, we quantify localization employing the inverse participation ratio (IPR) and the normalized participation ratio (NPR) and combine them into a single measure to create a phase map. The resulting diagrams reveal three regimes: a completely extended phase, a completely localized phase, and a mixed domain where localized and extended states coexist. In the diagrams, we investigate the behaviors of tightly and loosely wound helices and examine a special case where the number of sites per turn is a Fibonacci number. For moderate numbers of sites per helical turn, the mixed region is broad and also shifts with the long-range coupling. When the turn size is a Fibonacci number, the phase boundary becomes nearly horizontal and the mixed region fades out, effectively recovering the standard Aubry–André model behavior.

We investigate the magnetic properties of the system Fe₂(SO₄)(TeO₃)₂·3H₂O by susceptibility and high-field electron spin resonance (ESR) and dielectric measurements. The research reveals a dual magnetic ordering regime: short-range antiferromagnetic (AFM) correlations emerge at 53.6 K, followed by long-range AFM order at 32.0 K. A spin-flop transition is induced at 7 T (2 K) when the magnetic field aligns with the magnetically easy c-axis, accompanied by spin canting along the b-axis and antiparallel alignment of Fe³⁺ spins along the c-axis and chains. Weak ferromagnetism probably results from a significant Dzyaloshinskii–Moriya interaction. Notably, the compound shows a magnetically tunable dielectric behavior.

15R-BaMnO₃ as a perovskite manganite known for its antiferromagnetic and other physical properties, However, their transport properties, magnetoresistance (MR), temperature coefficient of resistance (TCR) and magnetic entropy change are rarely reported. In this work, these physical properties of the 15R-BaMnO₃ sample with uniform morphology and correct stoichiometry are investigated. Magnetic measurements show antiferromagnetic ordering below the Néel temperature (T_N≈233 K), with spins aligned ferromagnetically within planes and antiferromagnetically between layers. Below 50 K, spin canting induces weak ferromagnetism. Magnetotransport studies reveal significant negative MR, with a maximum of -11.6% at approximately 271 K under 6 T field. At 220 K, the TCR reaches its maximum value of 6.1%·K⁻¹ and reaches an excellent value of −3.06%·K⁻¹ near room temperature. Fitting the paramagnetic ρ(T) data to transport models indicates the existence of small-polaron (SP) hopping mechanism. The entropy change (ΔS_M), calculated via the Maxwell relation, reaching a maximum value of 0.133 J/kg·K at 49 K under 5 T. These results highlight the strong unique properties of crystal structure, magnetism, and transport behavior in 15R-BaMnO₃, filling the research gap in its transport and magnetocaloric fields.

Hydrogen energy is a zero-carbon, versatile clean energy source that serves as an ideal storage medium for renewable energy peak shaving and is the optimal choice for achieving large-scale, deep decarbonization in transportation, power, industry, and buildings. This paper addresses the key technical challenges in the catalytic conversion of ortho and para hydrocarbons during liquid hydrogen production. It systematically compares the catalytic performance, flow characteristics, and heat transfer efficiency of packed-bed and wall-mounted catalysts. Through a combination of experimental research and numerical simulation, it was found that wall-mounted catalysts significantly outperform traditional packed catalysts in terms of low pressure drop (pressure drop is only one-third of that of packed catalysts at flow rates of 5–10 m/s) and high hydrogen gas processing capacity (allowing for higher flow rates). The study also revealed the influence of the length-to-diameter ratio of the conversion column on catalytic performance: When the length-to-diameter ratio is between 1.5 and 5, the average conversion rate of para hydrogen increases by 4%, and the outlet temperature decreases by 37.6%. This study provides new insights for the efficient production of liquid hydrogen and lays the theoretical foundation for the large-scale application of wall-mounted catalysts in the field of cryogenic chemical engineering.

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.