Journal of Low Temperature Physics最新文献

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.

In rotating (^3)He superfluids, the Kelvin–Helmholtz (KH) instability of the AB interface has been found to follow the theoretical model above (0.4 , T_textrm{c}). A deviation from this dependence has been assumed possible at the lowest temperatures. Our NMR and thermal bolometer measurements down to (0.2 , T_textrm{c}) show that the critical KH rotation velocity follows the extrapolation from higher temperatures. We interpret this to mean that the KH instability is a bulk phenomenon and is not compromised by interactions with the wall of the rotating container, although weak pinning of the interface to the wall is observed during slow sweeping of the magnetic field. The KH measurement provides the only so far existing determination of the interfacial surface tension at temperatures down to (0.2 , T_textrm{c}) as a function of pressure.

A rapid and reliable quench detection is vital for high current superconducting magnet system to prevent irreversible damage to a magnet by the quench phenomenon. The method for detecting the occurrence of a resistive transition has been widely adopted in the superconducting magnet. In the case of the voltage monitoring by means of dedicated taps, the electron quench detection device (EQDD) conversion unit, which converts detected high voltages into voltage-drop signal, should be required in the superconducting high field magnet. The power source of traditional quench detecting system, which can monitor for superconducting magnet with middle power operation, is supplied through the power transformer since the transformer can provide galvanic isolation between circuits. On the other hand, in the case of the super high magnet systems such as Korea Superconducting Tokamak Advanced Research and International Thermonuclear experimental reactor, since the maximum operation current and voltage of the super high field magnet keep over 60 kA and 50 kV DC, a passive component, which has strong an isolation device and high dielectric resistor qualities, has been required in the super high field magnet. If the power transformer is adopted in the super high field magnet, it can cause high cost for volume capacity since it needs for higher dielectric resistance value over 500 MΩ. Authors proposed the wireless resonance antenna and multi-receiver coils which can keep high level of dielectric resistance value with stability. As well as, the wireless power charging unit can reduce system volume due to multi-charging receivers for one antenna. In this study, authors investigated the effect of inserted resonator (Sx) coil between antenna and receiver coils, as well as, evaluated the electric field and magnetic field among the resonance coils under 300 W 370 kHz RF power generator since the strong electro-magnetic fields by the resonance coils can affect the electron devices inside of the EQDD module.