Journal of Low Temperature Physics最新文献

CaAgP has been accepted as a nodal-line semimetal exhibiting unusual physical properties, such as anomalous magnetoresistance, high-mobility electron carriers (HMEC), and surface superconductivity. In this study, we performed angular-dependent Hall resistivity and magnetoresistance measurements on Pd-doped CaAgP single crystals, with the applied current oriented parallel (I // c) and perpendicular (I ⟂ c) to the c-axis. Analysis of the Hall resistivity using a two-carrier model reveals that the electron contribution was larger for the I ⟂ c configuration, which was more seriously influenced by the (001) surface. Moreover, the Hall resistivity exhibits different angular dependences between the high- and low-field regimes. These findings indicate that the HMEC are highly concentrated on the (001) surface. Meanwhile, the angular dependences of the magnetoresistance are interpreted as arising from the competition between two-dimensional weak antilocalization and three-dimensional weak localization, consistent with the presence of a torus-shaped nontrivial Fermi surface. Taken together, the Hall resistivity and magnetoresistance results demonstrate that Pd-doped CaAgP is a nodal-line semimetal hosting drumhead surface states on the (001) surface.

Carbon-fiber-reinforced polymers (CFRPs) are among the most promising structural materials for aerospace applications, particularly for systems operating at cryogenic temperatures, where high strength, low mass, and low thermal conductivity are essential. In this work, the thermal conductivity of a set of CFRP samples: T300 (67% 0(^circ )), T700 (62% 0(^circ )), HS40 (67% 0(^circ )/0(^circ )/0(^circ )/90(^circ )), HS40 (62% 0(^circ )/0(^circ )/0(^circ )/90(^circ )), M55J (0(^circ )), HS40 (67% 0(^circ )), HS40 (62% 0(^circ )), IMA (0(^circ )), and IMA (90(^circ )), was measured over the temperature range 100 mK to 20 K. Thermal conductivities were extracted using a new analysis method developed. The resulting temperature-dependent behavior for each sample is presented and compared with the existing literature.

Motivated by recent experimental findings on (hbox {UTe}_2) via NMR and specific-heat experiments, we theoretically explore the thermodynamic signatures of condensates with small superfluid density and characterize their physical properties. We identify a hidden superconducting phase (A_2) composed of spin-up Cooper pairs at lower temperature (T) and field (H) under ambient pressure of (hbox {UTe}_2) and show that (A_2) reappears at higher H for all three principal field directions, a-, b-, and c-axis. The phase-transition lines from the (A_1) phase with spin-down pairs to the (A_2) phase in the H-T plane are horizontal and common to all three axes. With increasing magnetic field, the magnetic energy gain of the spin-up pairs is greater than that of the spin-down pairs. This multiple-phase diagram is extended to these under pressure (P), resulting in a simple picture based on non-unitary spin-triplet pairing symmetry (^3B_{3u}), which enables us to consistently capture the evolution of the superconducting phases throughout the entire H-T-P phase space.

In this work, quantum mechanics theory was applied to the thermoacoustic heat pump, and a quantum mechanical model within a one-dimensional harmonic potential well, namely the quantum thermoacoustic heat pump micro-cycle (TAHPMC), was constructed. Based on this model, the coefficient of performance (text{C}text{O}text{P}) and heating rate (H) of the thermoacoustic heat pump were derived, and dimensionless form ({H}^{*}) of (H) was defined for further analysis. The effects of the characteristic width of the potential well (A) and the width ratio (y) on these two parameters were systematically analyzed. To achieve synergistic optimization of the two performance indicators, an optimization objective function (Omega) was established. Through numerical optimization, the parameter interval that optimizes the comprehensive performance of (text{C}text{O}text{P}) and ({H}^{*}) was identified, and it was proved that the reduction in heat leakage can significantly improve the heating capability of the thermoacoustic heat pump.

High-temperature superconductors such as REBa₂Cu₃O_7−x (REBCO) tape conductor and Bi₂Sr₂CaCu₂O_x (Bi-2212) superconducting round wires exhibit great promise for future high-field magnet applications due to their advantages including high-field performance and high current-carrying capacity. Among these, Bi-2212 demonstrates significant advantages in the design of magnets for accelerators, NMR, and similar applications, owing to its isotropic characteristics. After heat treatment, bridges formed between the filaments of the Bi₂Sr₂CaCu₂O_x superconducting round wires. The impact of these bridges on the current-carrying capacity has not been fully studied and understood, especially the influence of such bridges on the AC loss remains unclear. In this paper, based on the three-dimensional finite element method, numerical simulation studies are conducted using the Kim model and the power law model. Within the frequency range of 50 to 100,000 Hz, and under the condition where the transport current is I_c multiplied by 0.1 to 1, the influence mechanism of the bridging and connection degree of the Bi-2212 filaments on the AC loss is investigated. When the transport current is less than 0.5 times the value of I_c, compared with the ideal Bi-2212 multifilamentary wire without bridging, the bridges hardly affect the magnitude of AC loss. However, when the transport current is greater than 0.5 times value of I_c, the AC loss will rises significantly. As the volume of the bridge structure increases, the AC loss will increase by almost more than 10 times. Furthermore, when large current is transmitted in the low-frequency range, the AC loss will significantly increase due to the presence of the bridge. However, as the frequency increases, the AC loss gradually decreases and eventually approaches the AC loss value of the ideal Bi-2212 multifilamentary wire without the bridges. It suggests that for large current transmission, high frequency can alleviate the impact on the bridge.

We investigate the momentum- and frequency-resolved longitudinal spin response of the half-filled triangular-lattice Hubbard model in the (120^circ ) antiferromagnetically ordered state. Using a spiral Hartree–Fock (HF) reference state and the random-phase approximation (RPA), we calculate the longitudinal spectral function (S_L(textbf{q},omega )=-(1/pi )operatorname {Im}chi _L^R(textbf{q},omega )) along the high-symmetry path (Gamma rightarrow Krightarrow Mrightarrow Gamma ) for (U/t=6), 8, and 10. In contrast to the coherent transverse Goldstone sector, the longitudinal response forms a broad high-energy continuum with momentum-dependent ridge-like enhancements that remain embedded in the interband particle–hole spectrum. Full-spectrum moment analysis yields centroid ranges (omega _L^textrm{cen}/tsimeq 5.9)–6.7, 7.9–8.5, and 9.9–10.4 for (U/t=6), 8, and 10, respectively, demonstrating a systematic upward shift of the characteristic longitudinal energy scale with increasing interaction strength. The corresponding second-moment spectral width remains large and strongly momentum dependent, with a broad maximum (Gamma _L/tsimeq 3.2)–3.3 near K, and does not exhibit a uniform narrowing with increasing U/t. Fixed-momentum cuts further reveal distinct longitudinal structures at K and M, with principal enhancements near (omega /tsimeq 4.8) and 7.2, respectively, at (U/t=8). Within HF+RPA, the broad response originates from direct coupling of longitudinal amplitude fluctuations to interband particle–hole excitations in the electronic Stoner continuum, which prevents the formation of an isolated amplitude-mode pole. With increasing U/t, this high-energy Stoner sector is displaced upward and progressively separates from the low-energy spin sector; it should not be identified with the longitudinal response of the localized-spin Heisenberg model, which arises from multi-magnon processes beyond the present treatment. These results provide a finite-U itinerant description of longitudinal amplitude fluctuations as broad continuum responses rather than well-defined Higgs quasiparticles in the triangular-lattice Hubbard antiferromagnet.

Based on Maxwell’s equations, the heat conduction equation, and basic equations of elasticity, a two-dimensional (2D) axisymmetric coupled thermal–magneto–mechanical model for an insulated pancake coil with real dimensions is constructed and theoretically validated in a rigorous manner. Using finite element modeling, the effects of the system dump trigger time and background magnetic field on the quench behaviors of a high-temperature superconducting (HTS)-insulated pancake coil are systematically studied. To analyze the electromagnetic and mechanical behaviors of HTS coils, a 2D coupled electromagnetic–mechanical model is used to incorporate the effect of coil deformation on the critical current dependence. The effectiveness of the coupled model is validated by comparing the numerical results with published experimental data. Numerical simulations of a 2D HTS coil under an external electromagnetic field are performed using the fully coupled and sequentially coupled methods, respectively. The results indicate that increasing the time taken to trigger the system dump has no influence on the energy dissipation rate. Compared with sequential coupling, the maximum temperature of the coil increases significantly under the fully coupled formulation, and the maximum value is achieved at an earlier time. An apparent slope change in the radial strain rate is observed when the quench occurs, regardless of the magnitude of the background magnetic field. Under full coupling, the radial strain rate increases slightly, reaches its maximum value earlier, and then begins to decrease. During quench protection, the radial stress and strain reach their maximum values and then decrease as the temperature decreases. Under full coupling, the stress and strain reach their maximum values at a faster rate.

The Josephson oscillation of a Bose-Einstein condensate (BEC) in a double-well potential is typically characterized by the population imbalance between the two wells. Within the two-mode approximation, the dynamics of the center of mass of the condensate is predicted to coincide with that of the population imbalance. However, numerical simulations reveal a discrepancy between the dynamics of the center of mass and that of the population imbalance, indicating that the two-mode model fails to fully capture the dynamics of BEC Josephson oscillations. To address this limitation, a four-mode approximation is employed to describe the dynamics of the system. The four-mode model not only describes the dynamics of the population imbalance but also accounts for the oscillation of the center of mass, thereby explaining the origin of the discrepancy between the two-mode model and the simulation results. Moreover, we find that although higher-order excitation modes are always present in Josephson oscillations, the two-mode model can still describe the dynamics of the population imbalance. This phenomenon is explained by the interference of population oscillations between local states.

A new approach describing Luttinger Liquid with point-like impurity as field theory for the phase of scattering is developed. It is based on a matching of the electron wave functions at an impurity position point. As a result of the approach, an expression for non-local action has been taken. The non-locality of the theory leads to the convergence of the observed values in an ultraviolet region. It allows studying conductance of the channel up to electron–electron interaction strength of the order of unit. Expansion of the non-local action in small frequency powers makes possible to develop a new approach to the renormalization group analysis of the problem. This method differs from the “poor man’s” approach widely used in solid-state physics. We have shown, that in the Luttinger liquid “poor man’s” approach breaks already in two-loop approximation. We analyse the reason of this discrepancy. The qualitative description of the phenomenon is discussed in detail.

We investigate the quantum transport through a rectangular velocity barrier in the (alpha )-(mathcal {T}_3) lattice. The scattering states are solved analytically, and the transport properties including conductance, shot noise, and Fano factor are obtained by following the zero-temperature Landauer–Büttiker formalism. The velocity mismatch across the barrier reshapes oblique tunneling channels while preserving the perfect transmission at normal incidence. In particular, this velocity mismatch shifts the critical incident energy for super-Klein tunneling, where transport becomes nearly noiseless as the conductance approaches unity. At the Dirac point, the velocity modulation leaves the finite conductance minimum of the honeycomb limit intact, accompanied by a universal Fano factor peak. In the dice limit, however, both conductance and shot noise vanish at this point owing to channel depletion. In addition, a slow barrier facilitates the high-energy transport for the dice lattice, while a fast barrier can suppress it in both lattice limits.