Journal of Low Temperature Physics最新文献

In this work, we study the proximity effects in a single- and two-band superconducting three-dimensional heterostructure, described by two condensates (condensate 1 and condensate 2) in the presence of an external magnetic field perpendicular to the heterostructure. The distance between the interfaces of both condensates is given by the parameter (lambda '). We solve the time-dependent Ginzburg-Landau equations considering a Josephson-like coupling to explore properties such as magnetization, Gibbs free energy, and the Abrikosov vortex state. We propose three cases: case 1, both condensates are composed of a single-band; case 2, the condensates are composed of two bands; and case 3, condensate 1 has a single-band and condensate 2 has two bands. As a result, we highlight the variation of the first critical field and the novel vortex configurations induced by the proximity effect between the superconducting condensates. This phenomenon substantially influences the arrangement of vortices in each of the superconducting bands.

In this paper, the proposal for a new multichroic pixel camera for the QUBIC instrument is presented, which aims to measure the B-mode polarization of the cosmic microwave background. The camera features antenna-coupled magnetic microbolometers (MMB) read out by a microwave SQUID multiplexer and software-defined radio-based room-temperature electronics, which are specifically optimized for MMB readout. The architecture of the detectors and their readout system is introduced, and the main design considerations are also discussed. The initial results of the simulation study suggest that MMBs are capable of achieving background-limited detection of the sky when used in an instrument like QUBIC. Additionally, the time response of these detectors appears to be sufficiently fast for the given telescope scan speed and beam size.

This paper presents the detector developments for the Canfrac Axion Detection Experiment (CADEx), aiming at detecting dark matter axions and dark photons within the W-band. A proof of concept of the detection system is based on an array of lumped-element kinetic inductance detectors (LEKIDs). Microstrip technology is used as read-out scheme, and the ground plane acts as backshort for optimizing optical absorption in the W-band. A titanium/aluminum bilayer is used for ensuring detection below 100 GHz. The detector array design includes an inner active section consisting of 36 detectors for direct detection of the axion signal and an additional outer rim of 28 blind pixels for calibration purposes. The nanofabrication process and a preliminary cryogenic characterization are presented, being the results in good agreement with the frequency design. Measured devices exhibit coupling quality factors of the order of 6 × 10⁴, internal quality factors above 10⁵ and an estimated kinetic inductance of 3.3 pH/□.

In this research work, samples of Pr_0.8Sr_0.2MnO₃ were prepared using two methods: the conventional high-temperature ceramic method (sample R1) and the sol–gel method (sample R2) in order to form a composite. The Curie temperatures were found to be 161 K and 210 K for R1 and R2, respectively. We conducted a theoretical investigation of the magnetic and magnetocaloric (MC) properties of a composite constructed from R1 and R2 compounds to enhance the MC effect.The results suggest that our composite, with a Curie temperature evaluated at 190 K, could be a potential candidate for magnetic refrigeration. Refined values of the critical exponents β, γ, and δ, determined from the modified Arrott plots and the Kouvel–Fisher method, indicate that the behavior of the composite compound is consistent with the 3D Heisenberg model for T ≤ T_C and with the mean-field model for T > T_C.

The Gross–Pitaevskii equation is solved by analytic methods for an external double-well potential, that is, an infinite square well plus a (delta)-function central barrier. We find solutions that have the symmetry of the non-interacting Hamiltonian as well as asymmetric solutions that bifurcate from the symmetric solutions for attractive interactions and from the antisymmetric solutions for repulsive interactions. We present a variational approximation to the asymmetric state as well as an approximate numerical approach. We compare with other approximate methods. Stability of the states is considered.

Based on the characteristic change in the resistance of superconducting devices during the superconducting transition, a quantitative method to determine the temperature of superconducting devices has been proposed. This method can detect in real time whether the temperature of the superconducting device exceeds the superconducting transition temperature, thereby enabling quick reduction of the trapped magnetic flux in devices. We apply this method in our experiment, which uses a superconducting 22 subarrays programmable Josephson voltage standard device and obtains satisfactory results. We conclude that this method can efficiently reduce the trapped magnetic flux in superconducting devices and facilitate testing for measurement systems which do not possess thermometers.

We developed a cryogenic facility to assess the performance of different types of cryogenic mechanisms. The facility can host very large (up to (sim {1},hbox {m}^{3})) and heavy (up to (sim {30},hbox {kg})) instrumentation, cooled down below 10 K. The operation of moving components can be visually monitored by means of two webcams looking inside the 4 K volume. In addition a large number of electrical feedthroughs (444 lines) allow the operation of a set of hall and capacitive sensors to measure both the magnetic field, the position of moving devices with an accuracy of tens of microns and their temperatures with an accuracy of few (%). We present the results of the first tests on a large aperture (500 mm diameter) superconducting magnetic bearing for the SWIPE/LSPE experiment currently under test.

Using the strong coupling diagram technique, we find three phases of the half-filled isotropic Hubbard model on a triangular lattice at finite temperatures. The weak-interaction ((Ulesssim 5t)) and strong-interaction ((Ugtrsim 9t)) phases are similar to those obtained by zero-temperature methods—the former is a metal without perceptible spin excitations; the latter is a Mott insulator with the 120(^circ) short-range spin ordering. Zero-temperature approaches predict a nonmagnetic insulating spin-liquid phase sandwiched between these two regions. In our finite-temperature calculations, the Mott gap in the intermediate phase is filled by the Fermi-level peak, which is a manifestation of the bound states of electrons with pronounced spin excitations. We relate the appearance of these excitations at finite temperatures to the Pomeranchuk effect.

The Gross–Pitaevskii equation (GPE) in a double-well potential produces solutions that break the symmetry of the underlying non-interacting Hamiltonian, i.e., asymmetric solutions. The GPE is derived from the more general second-quantized Fock Schr(ddot{textrm{o}})dinger equation (FSE). We investigate whether such solutions appear in the more general case or are artifacts of the GPE. We use two-mode analyses for a variational treatment of the GPE and to treat the Fock equation. An exact diagonalization of the FSE in dual condensates yields degenerate ground states that are very accurately fitted by phase-state representations of the degenerate asymmetric states found in the GPE. The superposition of degenerate asymmetrical states forms a cat state. An alternative form of cat state results from a change of the two-mode basis set.

We present an analysis method for determining signal amplitudes using a least squares method in combination with an optimally selected bandpass filter. This method has been developed to process heat and light signals obtained in the AMoRE-I experiment. We apply Butterworth filters with various combinations of passbands and filter orders to both the heat and light signals. Subsequently, we employ the least squares method to calculate signal amplitudes by comparing each signal template for the heat and light channels. Optimal filter conditions are identified to achieve the best resolution value. In this paper, we provide a detailed description of the signal processing approach, comparing it with the optimal filter method.