Journal of Low Temperature Physics最新文献

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.

Nanocrystalline Ni_0.9−xZn_0.1Co_xFe₂O₄ (x = 0.2, 0.4, 0.6, 0.8) ferrites were synthesized via the sol–gel method, yielding a cubic single-phase spinel structure (Fd−3m), as confirmed through Rietveld refinement. The crystallite size was observed to increase from 7 to 10 nm with higher Co substitution. Magnetic characterization revealed a pronounced dependence on Co concentration, with zero-field-cooled and field-cooled magnetization curves exhibiting bifurcation indicative of magnetic relaxation phenomena. The Ni_0.5Zn_0.1Co_0.4Fe₂O₄ composition exhibited a blocking temperature of 191 K, a Curie temperature of 207 K, and a transition from ferromagnetic ordering at 5 K to superparamagnetic behavior at 300 K. Similarly, Ni_0.3Zn_0.1Co_0.6Fe₂O₄ demonstrated a transition at 251 K with retained ferromagnetic ordering at 5 K. In contrast, Ni_0.1Zn_0.1Co_0.8Fe₂O₄ displayed magnetic irreversibility and a paramagnetic state at 300 K. Raman spectroscopy further corroborated the inverse spinel structure, revealing characteristic vibrational modes at ~ 460 cm⁻¹ and 680 cm⁻¹. These findings underscore the pivotal role of Co substitution in modulating the structural and magnetic properties of Ni_0.9−xZn_0.1Co_xFe₂O₄ nanocrystals, particularly their temperature-dependent magnetic phase transitions. Collectively, the results highlight the influence of Co concentration on the structural and magnetic properties of Ni_0.9−xZn_0.1Co_xFe₂O₄ nanocrystals, particularly their temperature-dependent magnetic transitions.

We investigated the magnetocaloric effect (MCE) and thermodynamic properties of Magnetopolaron embedded in two-dimensional (2D) transition metal dichalcogenides (TMDs) under the canonical ensemble approach. From the results, we found that an increase in magnetic field considerably affects the magnetic moment alignment or brings an additional energy in 2D TMDs monolayers which is responsible for the energy exchange observed. The entropy change or MCE, which is more pronounced in the case of molybdenum and less for tungsten, affects the magnetic state of material. The combined effect of magnetic field and temperature has a great change on the magnetic state of 2D TMDs monolayer materials. The behavior of free energy obtained in the present paper can be used as a characteristic of paramagnetic materials. It comes that all 2D TMDs monolayers studied in the present manuscript present a paramagnetic aspect making them promising candidates for practical applications of magnetic refrigeration.

Using Monte Carlo simulations (MCS), we investigated the magnetic properties and phase diagrams of a hexagonal ferrimagnetic Ising nanotube with a core–shell structure composed of spin-5/2 and spin-2 particles, taking surface dilution into account. Our results revealed several characteristic behaviors. Notably, the concentration of magnetic atoms has a significant influence on both the critical and compensation temperatures. For low values of the exchange interaction ({J}_{s})​, dilution has no effect on the critical temperature. However, a compensation point appears beyond a dilution threshold, observed for (xge 0.6).We also identified critical thresholds for the crystal field anisotropies ({D}_{s})​ and ({D}_{c})​. Below these thresholds, the critical temperature remains nearly constant, then gradually increases and converges toward a saturation value once the thresholds are exceeded. Furthermore, the analysis of hysteresis loops shows that the system’s magnetic response is highly influenced by dilution: the remanent magnetization increases significantly in absolute value as the concentration of magnetic atoms rises from (0.6) to(1.0).

The paper presents the analytic expressions of nearest neighbor distance between two particle, Helmholtz free energy, thermodynamic and structural quantities for hcp crystals on the basis of the statistical moment method (SMM) taking into account of vibrational motion of particles, Helmholtz free energy and thermodynamic quantities for hcp crystals on the basis of the self-consistent field method (SCFM) taking into account of molecular motion. The theoretical results are applied to calculate numerically for hcp-N₂. Some numerical results are compared with experiments and other calculations.

This investigation explores the influence of temperature, radius, Aharonov–Bohm flux, and bandgap energy on the specific heat and magnetocaloric properties of graphene quantum dots. By enforcing the continuity condition of eigenspinors at the graphene quantum dots boundary, an analytical relation is derived, demonstrating the dependence of quantized energy levels on external physical parameters. The specific heat exhibits a Schottky-like anomaly, characterized by an initial rise with increasing temperature, reaching a maximum, followed by a subsequent decline. Enhanced magnetic fields induce a shift in the peak temperature while maintaining a consistent peak magnitude (~ 0.44 J/K). The magnetocaloric potential exhibits a monotonic increase with magnetic field intensity, converging to a saturation value of − 0.7 J/(kg⋅K) at elevated temperatures, where thermal fluctuations dominate. Furthermore, the magnetocaloric response demonstrates greater sensitivity to variations in bandgap energy and magnetic field strength compared to changes in the dot radius and Aharonov–Bohm flux.