Journal of Low Temperature Physics最新文献

The solution for a scarf type potential is obtained via the supersymmetric approach. The energy equation for any l-state is obtained in a closed and compact form. Some thermodynamic properties like the vibrational enthalpy, Gibbs free energy, heat capacity at constant pressure and entropy are obtained via the vibrational partition function from the energy level. The effect of temperature, potential depth and the screening parameter on these thermodynamic properties are examined. It was shown in the numerical computations that the different parameters have different variations with the thermodynamic properties.

We consider the stabilities and dynamical properties of solitons in one-dimensional spin-tensor-momentum-coupled Bose–Einstein condensates with periodical tunable Raman coupling by numerical simulating and variational approximating the time-dependent Gross–Pitaevskii equations. Our results show for a trapless system, the dynamically stabilized bright solitons can be formed by modulating Raman coupling with the initial state of polar soliton, and its evolution and movement show consistence with analytical prediction. The effects of oscillating frequency of Raman coupling are also investigated. In addition, the evolution of amplitudes of such solitons exhibits nontrivial mode with combination of two oscillations, which is different with the case of fixed Raman coupling. The periodically-modulating Raman coupling provides a new mechanism to stabilize the solitons in spin-tensor-momentum-coupled Bose–Einstein condensates, which would be beneficial for the potential study of soliton dynamics in experiment.

In recent years, there has been increasing interest in developing detectors which are sensitive to sub-GeV dark matter and low-energy events from coherent neutrino scattering. Due to carbon’s light atomic weight and its tendency to form crystals with high-energy, long-lived phonon modes, carbon-based crystals (including diamond and silicon carbide (SiC)) present themselves as natural target materials for scattering-based searches in this regime. We present our preliminary results in adapting our TES-based detectors to these substrates, specifically 4-H SiC and polycrystalline diamond. We focus on our fabrication efforts, specifically tuning the transition temperature ((text {T}_{text {C}})) of tungsten films sputtered on these materials, as well as our advancement toward fabricating and testing devices on these substrates.

We present a method for precise monitoring of the loop gain of transition edge sensors (TES) under electrothermal feedback. The measurement is implemented on the ICE DfMux electronics and operates simultaneously with Digital Active Nulling (DAN). It uses one additional bias sinusoid per TES and does not require any additional readout channels. The loop gain monitor is being implemented on the Simons Array and is an integral part of the baseline calibration strategy for the upcoming LiteBIRD satellite.

High quantum efficiency (QE) X-ray absorbers are needed for future X-ray astrophysics telescopes. The Advanced Telescope for High ENergy Astrophysics (ATHENA) mission requirements for the X-ray Integral Field Unit (X-IFU) instrument dictate, at their most stringent, that the absorber achieve vertical QE > 90.6% at 7 keV and low total heat capacity, 0.731 pJ/K. The absorber we have designed is 313 µm square composed of 1.05 μm Au and 5.51 μm electroplated Bi films (Barret et al. in Exp Astron 55:373–426, 2023). Overhanging the TES, the absorber is mechanically supported by 6 small legs whose 5 μm diameter is tuned to the target thermal conductance for the device. Further requirements for the absorber for X-IFU include a > 40% reflectance at wavelengths from 1 to 20 μm to reduce shot noise from infrared radiation from higher temperature stages in the cryostat. We meet this requirement by capping our absorbers with an evaporated Ti/Au thin film. Additionally, narrow gaps between absorbers are required for high fill fraction, as well as low levels of fine particulate remaining on the substrate and zero shorts between absorbers that may cause thermal crosstalk. The Light Element Mapper (LEM) is an X-ray probe concept optimized to explore the soft X-ray emission from 0.2 to 2.0 keV. These pixels for LEM require high residual resistance ratio (RRR) thin 0.5 µm Au absorbers to thermalize uniformly and narrow < 2 μm gaps between pixels for high areal fill fraction. This paper reports upon technology developments required to successfully yield arrays of pixels for both mission concepts and presents first testing results of devices with these new absorber recipes.

We present the optical characterization of two-scale hierarchical phased-array antenna kinetic inductance detectors (KIDs) for millimeter/submillimeter wavelengths. Our KIDs have a lumped-element architecture with parallel plate capacitors and aluminum inductors. The incoming light is received with a hierarchical phased array of slot dipole antennas, split into 4 frequency bands (between 125 GHz and 365 GHz) with on-chip lumped-element band-pass filters, and routed to different KIDs using microstriplines. Individual pixels detect light for the 3 higher-frequency bands (190–365 GHz), and the signals from four individual pixels are coherently summed to create a larger pixel detecting light for the lowest frequency band (125–175 GHz). The spectral response of the band-pass filters was measured using Fourier transform spectroscopy (FTS), the far-field beam pattern of the phased-array antennas was obtained using an infrared source mounted on a 2-axis translating stage, and the optical efficiency of the KIDs was characterized by observing loads at 294 K and 77 K. We report on the results of these three measurements.

We study different resonances (first of all of the Fano type) in the interference device formed by the Aharonov–Bohm ring with superconducting (SC) wire in the topologically nontrivial state playing a role of a bridge between top and bottom arms. We analyze Majorana modes on the ends of the SC wire and show that the collapse of the additional Fano resonance, that is initially induced by transport scheme asymmetry, is connected with the increase of the length of the bridge when the binding energy of the Majorana end modes tends to zero. In local transport regime, the Fano resonances are stable against the change of the transport symmetry. The reasons of both collapse and sustainability are analyzed using a spinless toy model including the Kitaev chain.

Vibrating probes when immersed in a fluid can provide powerful tools for characterising the surrounding medium. In superfluid (^3)He-B, a condensate of Cooper pairs, the dissipation arising from the scattering of quasiparticle excitations from a mechanical oscillator provides the basis of extremely sensitive thermometry and bolometry at sub-millikelvin temperatures. The unique properties of the Andreev reflection process in this condensate also assist by providing a significantly enhanced dissipation. While existing models for such damping on an oscillating cylinder have been verified experimentally, they are valid only for flows with scales much greater than the coherence length of (^3)He, which is of the order of a hundred nanometres. With our increasing proficiency in fabricating nanosized oscillators, which can be readily used in this superfluid, there is a pressing need for the development of new models that account for the modification of the flow around these smaller oscillators. Here we report preliminary results on measurements of the damping in superfluid (^3)He-B of a range of cylindrical nanosized oscillators with radii comparable to the coherence length and outline a model for calculating the associated drag.

We study Andreev reflection in a one-dimensional square-well pair potential. We discuss the history of the model. The current-phase relation is presented as a sum over Matsubara frequencies. How the current arises from bound and continuum levels is found by analytic continuation. We discuss two limiting cases of the square-well potential, the zero-length well and the infinite well. The model is quantitatively valid in some cases but forms the basis for understanding a wide range of problems in inhomogeneous superconductivity and superfluidity.

We report on simulations of a novel design of optical design of optical titanium nitride (TiN)-based Kinetic Inductance Detectors (KIDs) in order to improve in order to improve their response to optical photons. We propose to separate the meander from the substrate to trap hot phonons generated by optical photons, preventing their rapid propagation through the substrate. These phonons would in turn contribute to the breaking of more Cooper pairs, thereby increasing the response of the detector. In our design, the meander is suspended a few hundred nanometers above the substrate. Furthermore, reflective gold (Au) or aluminum (Al)-based layers can be placed under the meander to improve photon coupling in the optical wavelengths.