Journal of Low Temperature Physics最新文献

Theoretical understanding of spin dynamics in ferromagnets is a crucial question in spintronics. A recent work considered the dynamical equations for ferromagnets using Onsager’s irreversible thermodynamics with fundamental variables magnetization (vec {M}) and spin current (vec {J}_{i}). The resulting equations have the same structure as Leggett’s Fermi liquid theory for the nuclear paramagnet (^{3})He. Specifically, (partial _{t}vec {J}_{i}) contains a term varying as (partial _{i}vec {M}) that we interpret as associated with a vector spin pressure and a term giving a mean-field along (vec {M}), about which (vec {J}_{i}) precesses. (There is also a decay term in (partial _{t}vec {M}) not normally present in the Leggett equations, which are intended for shorter-time spin-echo experiments.) The present work applies Fermi liquid theory to (vec {J}_{i}) of ferromagnets. The resulting dynamical equation for (vec {J}_i) confirms the form of (vec {J}_i) found earlier using irreversible thermodynamics, but now the previously unknown exchange constant is given in terms of the quasiparticle interaction parameters of Fermi liquid theory. Our results indicate that study of spin currents in ferromagnets can yield information about the Fermi liquid coefficients.

This paper presents the design and experimental results of a helium liquefaction system with vibration damping capabilities, tailored for synchrotron radiation light source experiments. A 4.2 K GM cryocooler was utilized as the refrigeration source, integrated with a dedicated helium liquefaction system designed to cool and liquefy helium gas. This helium liquefaction device is suitable for scientific laboratory experiments. By analyzing the process of helium liquefaction, a method to improve liquefaction efficiency was proposed. The helium liquefaction rate was increased from 8.2 L/day at 1.1 bar (charging pressure) to a maximum of 15.9 L/day at 1.5 bar. To mitigate vibration effects from the reciprocating piston motion in the GM cryocooler, specialized vibration damping devices were installed to reduce transmitted vibrations to experimental apparatus. By employing welded bellows as vibration isolators, the system’s vibration amplitude was reduced from ± 9.0 μm in the X-axis, ± 9.0 μm in the Y-axis, and ± 21.0 μm in the Z-axis to ± 0.6 μm in the X-axis, ± 0.6 μm in the Y-axis, and ± 1.7 μm in the Z-axis.

This work investigates the electronic and thermodynamic properties of graphene within the framework of Doubly Special Relativity (DSR), emphasizing its role as an effective analog platform for analyzing modified dispersion relations. By incorporating the Dirac oscillator (DO) interaction and utilizing an energy-dependent effective mass for charge carriers in a magnetic field, we analyze how Planck-scale inspired deformations modify the energy spectrum and thermodynamic observables. We compare two structurally distinct DSR implementations: the Amelino–Camelia (AC) and Magueijo–Smolin (MS) models. Our results demonstrate that while the AC framework introduces significant nonlinear corrections and particle–antiparticle branch bifurcation, the MS corrections are strongly suppressed for massless carriers near the Dirac point. We establish a mapping to the Jaynes–Cummings (JC) and anti-Jaynes–Cummings (AJC) models, providing a bridge to quantum optical interpretation and trapped-ion simulations. While direct Planck-scale observations remain beyond current experimental reach, this study provides a controlled sensitivity analysis of how deformed kinematics propagate into solvable Dirac spectra within engineered analog gravity platforms.

We report a (^{139})La-NMR study of (textrm{Ba}_{2}textrm{La}_{2}textrm{CoTe}_{2}textrm{O}_{12}), (S=1/2) equilateral triangular-lattice antiferromagnet with easy-plane anisotropy at low temperatures. This compound undergoes a magnetic phase transition at (T_textrm{N} =) 3.26 K into an ordered state with the ({120}^circ) spin structure. Under magnetic fields above 3T, (T_textrm{N}) splits into (T_textrm{N1}) and (T_textrm{N2}), which correspond to the transitions from the paramagnetic phase to the up-up-down (uud) phase and from the uud phase to the triangular coplanar phase, respectively. The NMR spin-lattice relaxation rate (1/T_1) exhibits a critical divergence at (T_textrm{N1}), indicating the onset of long-range magnetic order. At (T_textrm{N2}), the NMR-linewidth measured at 5.4 T exhibits an anomalous decrease, which we attribute to a change in the spin structure from the uud to the triangular coplanar phase.

We theoretically investigate the superconducting gap structures in wallpaper fermions, which are surface states of topological nonsymmorphic crystalline insulators, based on a two-dimensional effective model. A symmetry analysis identifies six types of momentum-independent pair potentials. One hosts a point node, two host line nodes, and the remaining three are fully gapped. By classifying the Bogoliubov–de Gennes Hamiltonian in the zero-dimensional symmetry class, we show that the point and line nodes are protected by (mathbb {Z}_2) topological invariants. In addition, for the twofold-rotation-odd pair potential, nodes appear on the glide-invariant line and are protected by crystalline symmetries, as clarified by the Mackey–Bradley theorem.

It is widely believed that cuprates (i) must be strong-coupling superconductors, (ii) their superconducting phase curve is governed by phase fluctuations, and (iii) exhibit a loss of superfluid density with increasing overdoping, hand-in-hand with the fall in T_c. Here we examine these issues for several canonical cuprates in the light of their electronic specific heat. We find evidence for near-weak-coupling behaviour where the mean-field T_c is governed by the gap amplitude, and fluctuations in both amplitude and phase serve only to partially diminish T_c from this mean-field value. We also find that, over the doping range considered, the superfluid density is not depleted with overdoping. As such, this work questions several prevailing paradigms in cuprate physics [1].

At low temperatures, strong electronic correlations in many unconventional superconductors can induce a spin-density-wave (SDW) state as a result of Fermi-surface nesting and enhanced electron–electron interactions, and such SDW order is frequently observed to compete or coexist with superconductivity in correlated materials. In this work, we investigate the coexistence of SDW order and superconductivity using the Green’s function method in the Nambu representation, incorporating both electron–phonon-mediated pairing and pairing associated with SDW order at the antiferromagnetic wave vector. Two cases of gap equations are found to yield identical expressions for the superconducting critical temperature and the zero-temperature order parameter. Our results show that as the SDW order parameter increases, a larger coupling constant is required for superconductivity to emerge. Moreover, the gap-to-Tc ratio exceeds the BCS value at intermediate SDW strength and subsequently decreases to values below the BCS limit as the ratio of the zero-temperature SDW order parameter to the superconducting gap increases.

A comprehensive investigation of the structural, magnetic, and magnetocaloric properties of polycrystalline La_0.67−xGd_xCa_0.33MnO₃ (x = 0, 0.05, 0.1, 0.15, and 0.2), synthesized by the solid-state method, has been carried out. X-ray diffraction confirmed that all compositions crystallize in a single-phase orthorhombic Pbnm structure. A systematic decrease in the Curie temperature, from 257 K (x = 0) to 61 K (x = 0.2), was observed and attributed to the suppression of double-exchange interactions and the emergence of magnetic inhomogeneity. Most notably, the substitution of Gd led to a pronounced enhancement in the magnetic entropy change (|ΔS_M|), reaching a maximum of 11.24 J/kg K under a 5 T field for the x = 0.2 composition, which stands as one of the highest values reported for manganites. In addition, a secondary anomaly in the entropy change curves, particularly at elevated fields, was associated with a field-induced metamagnetic transition arising from the coexistence of paramagnetic and antiferromagnetic states above T_C. Critical behavior analysis based on Arrott plots further revealed that all samples exhibit a first-order magnetic phase transition. These simultaneous observations of exceptionally large ΔS_M values and metamagnetic features highlight the potential of these rare-earth-modified manganites for high-performance magnetocaloric applications.

The recombination rates of D atoms in solid D(_2) films were measured in the temperature range 0.23–(1.64,textrm{K}). Atoms were formed in thin D(_2) films by maintaining radio-frequency discharge above the film surface for several days. After stopping discharge the decay of D atoms concentrations was monitored at different temperatures by the method of electron spin resonance (ESR). Decreasing the films temperature from 1.64 to 0.23 K resulted in reducing the recombination rate from (7.2times 10^{-26},textrm{cm}^3textrm{s}^{-1}) to (1.0times 10^{-27},textrm{cm}^3textrm{s}^{-1}).

Superfluid helium-3 bolometers can be utilised for dark matter direct detection searches. The extremely low heat capacity of the B phase of the superfluid helium-3 at ultra-low temperatures offers the potential to reach world leading sensitivity to spin-dependent interactions of dark matter in the sub-GeV/c(^2) mass range. Here, we describe the development of bolometry using both micron scale and sub-micron diameter vibrating wire resonators, with a SQUID amplifier-based readout scheme. Characterisation of the resonators and bolometer measurements are shown, including the use of nonlinear operation and the corresponding corrections. The bolometer contains two vibrating wire resonators, enabling heat injection calibration and simultaneous bolometer tracking measurements. Coincident events measured on both vibrating wire resonators verify their response. We also demonstrate proof of concept frequency multiplexed readout. Development of these measurement techniques lays the foundations for the use of superfluid helium-3 bolometers, instrumented with vibrating nanomechanical resonators, for future low-threshold dark matter searches.