Journal of Low Temperature Physics最新文献

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.

Studies of astromaterials provide valuable insights into the formation and evolution of the solar system. To analyze such astromaterials on a sub-micrometer scale, one of the most useful tools is energy-dispersive X-ray spectroscopy (EDS) in conjunction with scanning transmission electron microscope (STEM). The conventional semiconductor-based EDS system is sometimes insufficient to resolve emission lines at closely adjacent energies. A transition edge sensor (TES) X-ray microcalorimeter is a promising solution to overcome this problem. We developed a 64-pixel TES X-ray microcalorimeter array which had an energy resolution of approximately 7 eV (FWHM) at an energy band from B Kα to Cu Kα. However, the counting rate was only approximately 1000 count/s/array. The distance between the detector and the sample is 30 cm, limited by the stage of the refrigerator. Therefore, an X-ray polycapillary is used to focus the X-ray, which focus size is 5 mm in diameter, resulting in a detection efficiency of only 5%. To increase the effective area, we developed a large size absorber with a large-scale array. A three-dimensional structure was created to fill the dead space between TES pixels. Additionally, an array of 224 elements was made to increase the detection efficiency by a factor of 10. In this paper, we provide more details of design, fabrication process of the overhang absorber, and device performance.

Inspired by recent remarkable sets of experiments on UTe(_2): discoveries of the fourth horizontal internal transition line running toward a tetra-critical point (TCP) at H = 15 T, the off-axis high-field phases, and abnormally large Knight shift (KS) drop below (T_textrm{c}) for (H parallel a)-magnetic easy axis, we advance further our theoretical work on the field (H)-temperature (T) phase diagram for (H parallel b)-magnetic hard axis which contains a positive sloped (H_textrm{c2}) departing from TCP. A nonunitary spin-triplet pairing with three components explains these experimental facts simultaneously and consistently by assuming that the underlying normal electron system with a narrow bandwidth characteristic to the Kondo temperature (sim)30 K unsurprisingly breaks the particle-hole symmetry. This causes a special invariant term in Ginzburg–Landau (GL) free energy functional which couples directly with the 5f magnetic system, giving rise to the (T_textrm{c}) splitting and ultimately to the positive sloped (H_textrm{c2}) and the horizontal internal transition line connected to TCP. The large KS drop can be understood in terms of this GL invariance whose coefficient is negative and leads to a diamagnetic response where the Cooper pair spin is antiparallel to the applied field direction. The present scenario also accounts for the observed d-vector rotation phenomena and off-axis phase diagrams with extremely high (H_textrm{c2}) (gtrsim)70 T found at angles in between the b- and c-axes and between the bc-plane and a-axis, making UTe(_2) a fertile playground for a possible topological superconductor.

While closing their famous paper entitled “Pseudogap: friend or foe of high-Tc?” Norman, Pines, and Kallin underlined that before we have a microscopic theory, we must have a consistent phenomenology. This was in 2005. As it turns out in 2006, a phenomenological theory of the pseudogap state was proposed by Gor’kov and Teitel’baum. This originated from their careful analysis of the Hall effect data, and it has been very successful model as numerous investigations over the years have shown. In this mini-review, the essence of the idea of Gor’kov and Teitel’baum is presented. The pseudogap obtained by them from the Hall effect data agrees very well with that obtained from the ARPES data. This famous Gor’kov–Teitel’baum thermal activation model (in short GTTA model) not only presents a consistent phenomenology of the pseudogap state, but also rationalizes the Hall angle data, and it presents a strong case against the famous “two-relaxation times” idea of Anderson and collaborators.