Journal of Low Temperature Physics最新文献

In this study, polycrystalline samples of Pr₂Mn₂O₆ (parent phase) and Pr_1.5A_0.5Mn₂O₆ (A = Mg, Ba) were prepared using the high-temperature solid-phase reaction method. The effects of Mg and Ba doping on magnetocaloric properties and critical behavior of the parent phase were systematically investigated. Under a magnetic field of 7 T, the relative cooling power (RCP) values of Pr₂Mn₂O₆, Pr_1.5Mg_0.5Mn₂O₆, and Pr_1.5Ba_0.5Mn₂O₆ were approximately 483.46 J·kg⁻¹, 428.22 J·kg⁻¹, and 479.88 J·kg⁻¹, respectively. The critical behavior analysis revealed that the parent phase showed short-range exchange interactions, while Pr_1.5A_0.5Mn₂O₆ (A = Mg, Ba) exhibited long-range exchange interactions. The temperature dependence of the order parameter n was studied under different magnetic fields, confirming the phase transition types and validating the accuracy of the critical exponents obtained. The research findings suggest that both the parent phase and Ba-doped ceramics at the A-site hold promise as magnetic refrigeration materials.

Cryogenic microcalorimeters are key tools for high-resolution X-ray spectroscopy due to their excellent energy resolution and quantum efficiency close to 100%. Multiple types of microcalorimeters exist, some of which have already proven outstanding performance. Nevertheless, they cannot yet compete with cutting-edge grating or crystal spectrometers. For this reason, novel microcalorimeter concepts are continuously developed. One such concept is based on the strong temperature dependence of the magnetic penetration depth of a superconductor operated close to its transition temperature. This so-called (lambda)-SQUID provides an in-situ tunable gain and promises to reach sub-eV energy resolution. Here, we present some design considerations with respect to the optimization of such a detector that are derived by analytic means. We particularly show that for this detector concept the heat capacity of the sensor should match the heat capacity of the absorber.

The Center for Axion and Precision Physics Research at the Institute for Basic Science in Republic of Korea is home to multiple active axion search experiments using cavity haloscopes that operate within the frequency range of 1–6 GHz. The haloscopes convert axions to photons, resulting in an output power of about 10({^{-24}})–10({^{-22}}) W. To detect such a small signal amidst noise, quantum-limited noise amplifiers and ultra-low-temperature environment (a few tenths of mK) are required for all critical readout components to minimize noise from all active and passive lossy components. Our primary objective is to achieve the highest possible scanning-frequency speed, which includes the time for maintenance and system calibration. This paper presents the development and operation of low-noise amplifiers for haloscope experiments targeting different frequency ranges and provides design, operational, and performance details of the amplifiers.

We overview and discuss several advances in the understanding of the motion of ions through solid helium. Positive and negative ions in solid helium are microscopic complexes with internal structures embedded into the host crystal lattice. Their low-field mobilities normally decrease with cooling in both bcc and hcp crystals of either isotope of helium ((^3)He and (^4)He). Depending on the density of solid helium (as well as, in the case of positive ions in hcp (^4)He, on the crystal orientation), the corresponding activation energies for the mobility of the two species of ions may or may not coincide, and they are found to be typically either equal to or about twice the vacancy creation energy. In strong electric fields, the field dependence of the drift velocity of ions is often nonlinear but monotonic. However, for positive ions in hcp (^4)He, non-monotonic anomalies in both temperature and field dependences of the drift velocity were observed. We discuss these features within the framework of the theory of ion motion via inelastic scattering of low-energy vacancions put forward by Alexander Andreev and co-workers.

Superconductivity and magnetism are competing effects that can coexist in certain regimes. Their co-existence leads to unexpected new behaviors that include the onset of exotic electron pair mechanisms and topological phases. In this work, we study the properties of a Josephson junction between two spin-split superconductors. The spin-splitting in the superconductors can arise from either the coupling to a ferromagnetic material or an external magnetic field. The properties of the junction are dominated by the Andreev bound states that are also split. One of these states can cross the superconductor’s Fermi level, leading to a ground-state transition characterized by a suppressed supercurrent. We interpret the supercurrent blockade as coming from a dominance of p-wave pairing close to the junction, where the electrons are at both sides. To support this interpretation, we analyze the different pairing channels and show that p-wave pairing is favored in the case where the magnetization of the two superconductors is parallel and suppressed in the anti-parallel case. We also analyze the noise spectrum that shows signatures of the ground-state transition in the form of an elevated zero-frequency noise.

Adsorption of ({}^4)He on graphene substrates has been a topic of great interest due to the intriguing effects of graphene corrugation on the manifestation of commensurate solid and exotic phases in low-dimensional systems. In this study, we employ worm algorithm quantum Monte Carlo to study helium adsorbed on a graphene substrate to explore corrugation effects in the grand canonical ensemble. We utilized a Szalewicz potential for helium–helium interactions and a summation of isotropic interactions between helium and carbon atoms to construct a helium–graphene potential. We implement different levels of approximation to achieve a smooth potential, three partially corrugated potentials, and a fully ab initio potential to test the effects of corrugation on the first and second layers. We demonstrate that the omission of corrugation within the helium–graphene potential could lead to finite-size effects in both the first and second layers. Thus, a fully corrugated potential should be used when simulating helium in this low-dimensional regime.

The solution for a scarf type potential is obtained via the supersymmetric approach. The energy equation for any l-state is obtained in a closed and compact form. Some thermodynamic properties like the vibrational enthalpy, Gibbs free energy, heat capacity at constant pressure and entropy are obtained via the vibrational partition function from the energy level. The effect of temperature, potential depth and the screening parameter on these thermodynamic properties are examined. It was shown in the numerical computations that the different parameters have different variations with the thermodynamic properties.

We consider the stabilities and dynamical properties of solitons in one-dimensional spin-tensor-momentum-coupled Bose–Einstein condensates with periodical tunable Raman coupling by numerical simulating and variational approximating the time-dependent Gross–Pitaevskii equations. Our results show for a trapless system, the dynamically stabilized bright solitons can be formed by modulating Raman coupling with the initial state of polar soliton, and its evolution and movement show consistence with analytical prediction. The effects of oscillating frequency of Raman coupling are also investigated. In addition, the evolution of amplitudes of such solitons exhibits nontrivial mode with combination of two oscillations, which is different with the case of fixed Raman coupling. The periodically-modulating Raman coupling provides a new mechanism to stabilize the solitons in spin-tensor-momentum-coupled Bose–Einstein condensates, which would be beneficial for the potential study of soliton dynamics in experiment.

In recent years, there has been increasing interest in developing detectors which are sensitive to sub-GeV dark matter and low-energy events from coherent neutrino scattering. Due to carbon’s light atomic weight and its tendency to form crystals with high-energy, long-lived phonon modes, carbon-based crystals (including diamond and silicon carbide (SiC)) present themselves as natural target materials for scattering-based searches in this regime. We present our preliminary results in adapting our TES-based detectors to these substrates, specifically 4-H SiC and polycrystalline diamond. We focus on our fabrication efforts, specifically tuning the transition temperature ((text {T}_{text {C}})) of tungsten films sputtered on these materials, as well as our advancement toward fabricating and testing devices on these substrates.