Journal of Low Temperature Physics最新文献

We describe a newly developed top-loading ⁴He sorption refrigerator. The top-loading configuration allows for rapid sample exchange, efficient cooling, and modular probe construction. A prototype comprises a condenser, an evaporator, a charcoal adsorption pump, and a top-loading probe, precooled by a Gifford–McMahon cryocooler. The base temperature and hold time in single-shot mode are 0.95 K and 2.5 h, respectively. The prototype provides a useable cooling power of 1.85 mW at 1 K.

This study explores quantum information dynamics in asymmetrically coupled double quantum dots, analyzing the effects of symmetry, initial state, and Coulomb interactions on correlation preservation. Results show that symmetry enhances entanglement robustness, while asymmetry and high entanglement increase sensitivity to decoherence. Strong Coulomb interactions support fidelity and capacity retention. These insights are relevant for optimizing protocols such as dense coding and teleportation in decohering environments.

Superconducting cables with complex multi-stage helical structures are essential components of the superconducting magnet systems of the International Thermonuclear Experimental Reactor. These cables often experience contact issues that can adversely affect their conductive properties. This study introduces a three-dimensional numerical model designed to accurately analyze the contact characteristics of multi-stage superconducting cables subjected to tensile strain. The model begins by defining the multi-stage geometry of the cable, and then evaluates the distribution of contact pressures and contact regions across individual strands. The numerical model was validated through comparison with existing reference data. An average contact force is introduced to quantify the magnitude of contact force on each strand. The study analyzes the effects of variations in the helical pitches of each stage of the cable on contact characteristics, as well as the influence of changes in the helical pitches of lower-stage cables on the contact characteristics of higher-stage cables. This research enhances the understanding of contact characteristics in multi-stage superconducting cables and provides valuable insights for optimizing the design of advanced hierarchical helical structures.

CaMnO₃, a perovskite manganite known for its antiferromagnetic (AFM) and other physical properties, has underexplored transport properties and temperature coefficient of resistance (TCR). We report exceptional charge transport phenomena in orthorhombic CaMnO₃, revealing a record negative temperature coefficient of resistance (TCR =  − 31.8% K⁻¹ at 21 K) for antiferromagnetic insulators. Magnetic characterization shows a Néel temperature (T_N) of 81.5 K. This magnetic transition govern distinct charge transport regimes, variable-range hopping (VRH) below T_N and small polaron (SP) conduction above T_N, demonstrating the existence of magnetic-electric coupling. Remarkably, the material exhibits field-independent TCR stability up to 6 T and significant magnetoresistance (MR =  − 17.5% at 22 K). These findings demonstrate CaMnO₃ potential for antiferromagnetic spintronic applications, particularly in magnetic sensors and spin-engineered thermal detection technologies in extreme environments.

Helium sorption coolers are widely used for achieving sub-kelvin temperatures due to their advantages of no moving parts, simple structure, and high reliability. While research has primarily focused on system design and sorption characteristics, studies on the condensation process of helium gas in these coolers remain limited. In this study, a three-dimensional simulation model is developed based on a laboratory helium sorption cooler prototype using helium-4 (4He) as the working fluid. The cooler reaches a minimum temperature of 827 mK with a holding time of 20 h. Experimental validation confirms the high accuracy of the model. The study analyzes the flow dynamics of liquid helium during condensation. Liquid helium flows along the narrow walls of the condenser heat exchanger, enters the evaporator through the pump tube, and evaporates, lowering the evaporator temperature. The evaporated helium gas then rises through the center of the pump tube. The study also examines the effect of pre-cooling temperature and operating pressure on the cooling rate. A decrease in pre-cooling temperature from 3.3 to 3.2 K leads to a sharp increase in the cooling rate, with cooling time dropping from 167 to 123 s. As the pre-cooling temperature further drops, the cooling time continues to decrease, but the impact on the cooling rate diminishes. Similarly, increasing the operating pressure from 37 to 41 kPa accelerates the cooling process initially, but the impact lessens as pressure continues to rise.

The superconductors with Kagome lattice have recently attracted significant interest due to their unconventional superconducting properties. Here, we present a comprehensive investigation of the superconducting properties of the Re-based hexagonal C14 Laves alloys TRe(_{2}) (T = Zr and Hf), which contain a hexagonal diamond lattice of T atoms and a breathing Kagome lattice of Re atoms. The electrical resistivity, magnetization, and specific heat measurements confirm type-II bulk superconductivity with T(_{C}) = 6.1 K for ZrRe(_{2}) and 5.8 K for HfRe(_{2}). The superconducting parameters, such as the lower and upper critical field, the coherence length, the penetration depth, the electron–phonon coupling constant, and the density of electronic states at Fermi energy level, are comparable with those of other hexagonal C14 Laves compounds with the same crystal structure. In particular, the values of these parameters are quite close to those of the BCS theoretical framework, suggesting that both ZrRe(_{2}) and HfRe(_{2}) are weakly coupled type-II superconductors as other hexagonal C14 Laves alloys.

Vapor-filled multielectron bubbles (MEBs) in liquid helium offer an ideal system for studying two-dimensional electron systems in a curved geometry. In the normal state of the liquid, the bubbles can contain a substantial amount of helium vapor alongside electrons, which in turn affects the surface electron densities. In this work, we experimentally demonstrate control over both the growth and collapse of vapor-filled MEBs in liquid helium-4 by engineering the convective fluid flow within the experimental cell. We believe this simple technique can facilitate tuning the electron density, and thus, future studies on electron phases inside MEBs.

In this work, we design and fabricate the transimpedance amplifier (TIA) following the design mentioned in Liang (Ultramicroscopy, 267:114051, 2024). In the TIA, the pre-amplifier (Pre-Amp) is made of a junction field-effect transistor (JFET) that can work at 77 K. The post-amplifier (Post-Amp) is made of an operational amplifier. Cascade Pre-Amp and Post-Amp to form the inverting amplifier. With a 1.13 G(Omega ) feedback network, the gain of TIA is 1.13 G(Omega ) and its bandwidth is about 97 kHz. The equivalent input noise voltage power spectral density (PSD) of TIA is not more than 9 (nV)(^2)/Hz at 10 kHz and 4 (nV)(^2)/Hz at 50 kHz, and its equivalent input noise current PSD is about 26 (fA)(^2)/Hz at 10 kHz and 240 (fA)(^2)/Hz at 50 kHz. The measured electrical performances and noise performances of TIA are consistent with the simulations and calculations. As an example, the realization of TIA in this work verifies the design method and analytical calculations for the low-noise large-bandwidth high-gain TIA proposed in Liang (Ultramicroscopy, 267:114051, 2024), Liang (Ultramicroscopy, 234:13466, 2022). And, the TIA in this work is perfect for the cryogenic STM working at liquid nitrogen temperature. With this TIA, at 77 K, the scanning tunneling spectroscopy and scanning tunnel shot noise spectroscopy measurements can be performed at the frequency of tens of kHz, even in the case of high tip–sample resistance.

A two-stage tuned amplifier has been developed and characterised for operation at cryogenic temperatures for Penning Trap application. Two pHEMT devices were tested at 300 K, 77 K and 4.2 K for their DC and AC characteristics. The developed amplifier has shown an amplification of 40 dB at a quiescent power consumption of ~ 1 mW at liquid helium temperature. Considering the feeble intensity of the image charge signal from Penning trap, the input impedance of the first stage amplifier is kept high whereas the output impedance of the second stage is kept 50 Ω for impedance matching with the transmission line. The bandwidth was ~ 200 kHz with the centre frequency around 40 MHz to match with the axial frequency of the electrons confined in the Penning trap. The amplifier was tested at 5 T magnetic field and it showed similar performance as in no field condition. The signal of trapped electrons, in a Penning trap at 4.2 K, was detected using this amplifier through the resonance absorption technique, confirming its suitability for the system.