Journal of Low Temperature Physics最新文献

We investigate the properties of liquid (^4)He in both the normal and superfluid phases using path-integral Monte Carlo simulations and recently developed ab initio potentials that incorporate pair, three-body, and four-body interactions. By focusing on the energy per particle as a representative observable, we use a perturbative approach to quantify the individual contributions of the many-body potentials and systematically propagate their associated uncertainties. Our findings indicate that the three-body and four-body potentials contribute to the total energy by approximately 4% and 0.5%, respectively. However, the primary limitation in achieving highly accurate first principles calculations arises from the uncertainty in the four-body potential, which currently dominates the propagated uncertainty. In addition to the energy per particle, we analyze other key observables, including the superfluid fraction, condensed fraction, and pair distribution function, all of which demonstrate excellent agreement with experimental measurements.

In the framework of the Gross-Pitaevskii theory, based on the double-parabola approximation method, we successfully found the expressions for dispersion relations of three NG modes of two immiscible Bose-Einstein condensates restricted by a hard wall (two phonons and a ripplon). For the first condensate component, which is not confined by a hard wall, we found one phonon and one ripplon. Meanwhile, for the second component confined by a hard wall, we found only one phonon (the dispersion relation depends on the position of the hard wall), and this manifests explicitly the finite-size effect.

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.

The evolution of a vortex line following the binormal flow equation (i.e. with a velocity proportional to the local curvature in the direction of the binormal vector) has been postulated as an approximation for the evolution of vortex filaments in both the Euler system for inviscid incompressible fluids and the Gross–Pitaevskii equation in superfluids. We address the issue of whether this is a suitable approximation or not and its degree of validity by using rigorous mathematical methods and direct numerical simulations. More specifically, we show that as the vortex core thickness goes to zero, the vortex core moves (at leading order and for long periods of time) with a velocity proportional to its local curvature and the binormal vector to the curve. The main idea of our analysis lies in a reformulation of the Gross–Pitaevskii equation in terms of associated velocity and vorticity fields that resemble the Euler system written in terms of vorticity in its weak form. We also present full numerical simulations aimed to compare Gross–Pitaevskii and binormal flow in various physical situations of interest such as the periodic evolution of deformed vortex rings and the reconnection of vortex filaments.

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.