Journal of Low Temperature Physics最新文献

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.

The effects of vacuum and oxygen annealing on Sr_2-xNb_xIrO₄ samples have been systematically investigated. The annealing under vacuum leads to an enhanced insulating state of the Sr_2-xNb_xIrO₄ compounds, which could be due to the evaporation of oxygen atoms which breaks the superexchange interaction between Ir and O ions. The annealing under oxygen atmosphere results in substantial straightening of the in-plane Ir–O–Ir bond and rapid depression of the canted antiferromagnetic ordering state. Importantly, the insulator-to-metal transition has been achieved by oxygen annealing of the Sr_2-xNb_xIrO₄ samples, which could be due to the enhanced hybridization of Ir 5d orbitals with the neighboring O 2p orbitals. The present results suggest that the annealing treatment could be an effective way for exploring of novel physical phenomena in Sr₂IrO₄ and related compounds.

High sensitivity and low noise of superconducting quantum interference devices make them ideal for reading the minute changes in resistance of a transition-edge sensor, which occurs when it absorbs energy or power. A series of first-order gradient, cross-coupling octagonal SQUIDs specifically tailored for use in TES were developed and fabricated for the advantage of lower parasitic capacitance compared with the overlap-coupling ones. It is obtained that a lower screening parameter and increased shunt resistance per junction lead to a higher flux-to-voltage transfer coefficient. This enhancement significantly boosts detection sensitivity and effectively minimizes noise contributions from electronics operating at room temperature. The low-temperature measurement results of the sample with an input coil of 3.5 turns indicate that a small device current white noise of 4.8 pA/√Hz, a device flux white noise of 1.1 μΦ₀/√Hz, and an optimal flux-to-voltage transfer coefficient of 338.2 μV/Φ₀ are achieved. The bandwidth of a SQUID current sensor with a smaller inductance of the input coil and a larger shunt resistance exceeds 10 MHz. SQUID current sensors, featuring octagonal structures with the first-order gradient cross-coupling, exhibit low flux noise, low current noise, and a high flux-to-voltage transfer coefficient, which can satisfy the requirements of TES applications.

Erbium orthophosphate ErPO₄ was successfully prepared. The XRD pattern analyses have proved that the ErPO₄ crystallizes in the tetragonal structure (I4₁/amd). Under a magnetic field of 50 kOe, the magnetic entropy change (− ΔS_M) reaches 23.78 J/kg K at 2.6 K for ErPO₄. The value of the relative cooling power is 475 J/kg. The lowest temperature and the large MCE have inferred that ErPO₄ is a potential candidate for sub-kelvin magnetic refrigeration applications.