Journal of Low Temperature Physics最新文献

The paper presents analytic expressions of the Helmholtz free energy, the crystal parameters, the nearest neighbor distance between two atoms, the isothermal compressibility, the thermal expansion coefficient, the heat capacity at constant volume, the Gruneisen parameter, the isothermal elastic modulus, the Young modulus, the mean squared displacement and the Debye–Waller factor for FCC monoatomic crystal builded by the statistical moment method. The paper performs numerical calculation of the obtained theoretical results for FCC quantum crystals ³He and ⁴He using the Lennard–Jones (6–12) pair interaction potential and the coordination sphere method. Some calculated results are compared with the experimental data and other calculations.

We propose a multi-spin Ising model to report a computational study of a mixed spin-1 and spin-1/2 ferrimagnetic nanoisland. Employing the finite cluster approximation (FCA), we thoroughly examine how the four-spin interaction, next-nearest neighbor interaction, and crystal field affect the phase diagrams and the magnetic properties including magnetizations, internal energy, and specific heat. The exact calculations derived from the Hamiltonian at the ground state (T = 0) reveal the existence of a critical equation, J′ + J₄ = − 4J_s delimiting two distinct ground states (I) and (II). Phase diagrams analysis shows that the transition temperature T_c trends toward a tricritical point as the four-spin interaction J₄ varies, without evidence of compensation phenomena; while the next-nearest neighbor interaction J' leads to the manifestation of compensation points only if J′ surpasses a J_s-dependent threshold value. Interestingly, when the crystal field D_S is inserted, one, two, or three compensation points may emerge according to the strength of J′.

Using the strong coupling diagram technique, we calculate the zero-temperature density of states (rho) of electrons on a square lattice immersed in a perpendicular uniform magnetic field. The electrons are described by Hubbard Hamiltonian. For moderate doping, Landau subbands are observed for small Hubbard repulsions U only. For larger U, the subbands are blurred. Instead, small peaks varying with the field induction B arise by opening the Mott gap in its vicinity. The related variation of (rho) with 1/B may be connected with the low-frequency quantum oscillations in lightly doped cuprates. For all considered repulsions, (rho) has gaps near transfer frequencies of the Hubbard atom, (-mu) and (U-mu), with (mu) the chemical potential. In the heavily underdoped case (mu <0), Landau subbands are grouped into the lower and upper Hubbard subbands for moderate and large repulsions. The intensity of the upper Hubbard subband decreases with approaching the Fermi level to the lower edge of the spectrum and finally vanishes.

We describe the design and performance of the cryostat and the multi-stage sub-K single-shot sorption cooler for the MIllimeter Sardinia Radio Telescope Receiver based on Array of Lumped elements kids (MISTRAL) experiment. MISTRAL is a W-band (77 - 103 GHz) Ti/Al bi-layer Lumped Elements Kinetic Inductance Detectors (LEKIDs) camera working at the Gregorian focus of the 64 m aperture Sardinia Radio Telescope (SRT), located in Sardinia (Italy). The cryogenic system, based on a 1.5 W at 4.2 K Pulse Tube (PT) cryocooler, provides the 4 K base temperature for the sub-K refrigerator, and cools down the cold optics and the filters chain of the instrument. The sub-K sorption cooler consists of two intermediate stages, (^{4})He and (^{3})He sorption refrigerators that allow to reduce the heat load on the ultra-cold head, and a twin stage of (^{3})He sorption refrigerator providing the 0.2 K operation temperature for the 415-pixel array of LEKIDs. MISTRAL experiment was installed at SRT in May 2023, the technical commissioning started in June 2023. We will show the performance of the system in the laboratory.

In the context of axion search in the BabyIAXO and IAXO helioscopes, various types of cryogenic detectors are investigated as high energy resolution, low energy threshold alternatives for the standard micromegas X-ray detectors. The setup presented in this paper comprising metallic magnetic calorimeter (MMC) X-ray detectors, a cryogenic local muon veto read out by an MMC, and internal and external lead shields, aims at establishing the background level that can be reached with MMCs in an above-ground experimental site. The low background setup is described in detail, and first observations from a low-temperature run are presented.

The low-temperature T-linear resistivity is a generic feature in the strange metal phase of overdoped cuprate superconductors; however, its origin is still not well understood. Based on the t–J model and the full charge-spin recombination scheme, the temperature dependence of electrical resistivity in the strange metal phase of the optimally doped and overdoped cuprates is studied. It is shown that at the optimal doping, the resistivity develops a linear-in-temperature behavior, while in the overdoped regime, the resistivity exhibits a nonlinear behavior which contains T-linear and T-quadratic components. The T-linear resistivity is thought to be dominated by isotropic inelastic scattering in the nodal region of the Fermi surface, where the most quasiparticle spectrum weight is assembled at around the tips of Fermi arcs.

Mechanical objects have been widely used at low temperatures for decades, for various applications; from quantum fluids sensing with vibrating wires or tuning forks, to torsional oscillators for the study of mechanical properties of glasses, and finally micro and nano-mechanical objects with the advent of clean room technologies. These small structures opened up new possibilities to experimentalists, thanks to their small size. We report on the characterization of purely metallic goalpost nano-mechanical structures, which are employed today for both quantum fluids studies (especially quantum turbulence in (^4)He, (^3)He) and intrinsic friction studies (Two-level-systems unraveling). Extending existing literature, we demonstrate the analytic modeling of the resonances, in good agreement with numerical simulations, for both first and second mechanical modes. Especially, the impact of the curvature of the whole structure (and therefore, in-built surface stress) is analyzed, together with nonlinear properties. We demonstrate that these are of geometrical origin and device-dependent. Motion and forces are expressed in meters and Newtons experienced at the level of the goalpost’s paddle, for any magnitude or curvature, which is of particular importance for quantum fluids and solids studies.

In this study, polycrystalline samples of La_0.7Ca_0.3-xDy_xMnO₃ (x = 0, 0.15) were synthesized via the solid-state reaction method. Their structures, magnetic properties, magnetocaloric effects, and critical behaviors associated with phase transitions were systematically investigated. All samples exhibited structures belonging to the Pbnm space group, characterized by precise compositions and good single-phase. The samples underwent paramagnetic-ferromagnetic (PM-FM) phase transitions at Curie temperatures (T_C) of approximately 244 K for x = 0 and 132 K for x = 0.15. The incorporation of Dy significantly broadened the half height wide temperature range (ΔT_FWHM) from 39.36 K (x = 0) to 121.92 K (x = 0.15). Consequently, the relative cooling capacity (RCP) of the samples was markedly increased, rising from 369.76 J·kg⁻¹ (x = 0) to 721.09 J·kg⁻¹ (x = 0.15). Furthermore, upon doping with x = 0.15, the phase transition type shifted from the first-order phase transition (FOPT) of the parent phase to a second-order phase transition (SOPT). This shift is attributed to the substitution of some Ca²⁺ ions by Dy³⁺, which weakened the double-exchange interaction and altered the phase transition type. Analysis of the critical behavior using the Kouvel-Fisher (K-F) and Modified Arrott plot (MAP) methods revealed that the critical features of the phase transition in La_0.7Ca_0.15Dy_0.15MnO₃ are better described by a Mean-Field Model with long-range ordering. Therefore, this study not only enriches our understanding of the physical properties of this class of materials but also enhances their potential for magnetic refrigeration (MR) applications.

When the frequencies (omega _A) and (omega _B) for trapping A- and B-species, respectively, in a binary Bose–Einstein condensates are tuned so that the mixture is in a special status, then all the parameters would fulfill a special relation. It implies that in this case the unknown parameter can be determined by the known parameters. In this paper, (omega _A) and (omega _B), which can be accurately controlled, are tuned so that the two clouds of this system either overlap completely with each other or one cloud just disappears from the center. In each case, based on the analytical solution of the coupled Gross–Pitaevskii equations which is obtained under the Thomas–Fermi approximation, two formulae relating to the parameters have been derived. When the two intraspecies interactions have been known, the interspecies interaction can be thereby determined via these formulae.