Journal of Low Temperature Physics最新文献

Considering both interspecies and intraspecies quantum fluctuations in quasi-one dimensional ultracold Bose–Bose mixtures, we show that new LHY-like effects lead to generalized stability conditions against collapse and phase separation. Moreover, we demonstrate that the stability of self-bound droplets is enhanced by interspecies correlations. The contribution to the energy of the quadratic fluctuations is shown to have negligible effects in the Bogoliubov approximation.

In recent years, as two-dimensional (2D) materials have been widely used in electronic devices, searching for 2D high superconducting transition temperature ((T_{c})) superconductors has also attracted great attentions. In this work, based on first-principles calculations and Eliashberg equation, the electronic structure, electron-phonon coupling (EPC) and possible superconductivity of alkali metal-deposited monolayer BC: MBC (M = Na, K) are studied. The results show that MBC (M = Na, K) are metallic and potential superconductors. The calculated EPC constants of MBC (M = Na, K) are 0.97 and 1.48, respectively. The strong coupling of MBC (M = Na, K) mainly origins from the coupling between electrons with the in-plane vibration modes of C and B atoms. The (T_{c}) of MBC (M = Na, K) are 34.1 K and 41.7 K, respectively, and the (T_{c}) of NaBC can be increased to 45.6 K under 2% biaxial tensile strain, and the (T_{c}) of KBC can be boosted to 53.8 K under 1% biaxial tensile strain. It is anticipated that the predicted monolayer MBC (M = Na, K) and its strained cases can be realized in future experiments.

In this study, we investigate the thermal properties of the relativistic Klein-Gordon oscillator with non-minimal coupling in one, two, and three dimensions within the framework of superstatistics theory. We focus on three distinct distributions: Gamma, Log-Normal, and F-distributions, each described by a specific probability density function (f(beta )). To compute the partition function, we apply the Euler-MacLaurin formula, incorporating the low-energy asymptotics approximation of superstatistics and accounting for the remainder term (R_{i}). Our study involves a detailed analysis of how entropy (S) and specific heat (C_{v}) vary with temperature (1/beta) and the universal parameter (q), based on the derived partition functions. The variations in these thermodynamic quantities are explored across different dimensionalities and statistical frameworks, providing insights into the interplay between statistical distributions and the thermal dynamics of the system. This approach allows us to understand the influence of non-equilibrium conditions and fluctuating temperature fields on the behavior of relativistic quantum systems. By extending the analysis to multiple dimensions and distribution types, we aim to offer a comprehensive view of how superstatistical distributions affect the thermodynamic properties of the Klein-Gordon oscillator, thus contributing to the broader understanding of thermal dynamics in relativistic systems.

Several experiments are currently carried out to measure the magnitude of the B mode polarization of the cosmic microwave background (CMB). It is a strong indicator of the presence of gravitational waves from the early universe inflationary epoch. As the average variations of the B mode components of the CMB are expected to be of the order of a few tens of nK or below, the detection of these polarized signals requires an ultrasensitive system. This article is focused on CMB detection at frequencies around the 150 GHz band of the electromagnetic spectrum, near the peak of the CMB 2.7K blackbody band of the EM spectrum. We propose a readout system for CMB cryogenic detection based on a software-defined radio (SDR) that uses frequency division multiplexing (FDM), a Goertzel channelizer and a radio frequency microwave SQUID multiplexer ((mu)MUX) working at the cryogenic temperatures of (approx) 320mK. These interfaces can be used to read an array of 1024 magnetic microbolometers (MMBs) as detectors that are photon-limited for CMB detection in the band of interest. As part of the requirements for these measurements, we introduce a design of the detection and read out chain and show its expected performance and potential implementation. The proposed system can read the desired number of detectors from an array in a modular way, which allows future expansions, and its frequency division multiplexing system improves the cooling capacity of the cryostat by minimizing the amount of active cryogenic electronics. In this article, we first describe this proposed FDM readout chain and then present noise measurements of a test implementation.

The Berry phase is a fundamental concept in quantum mechanics with profound implications for understanding topological properties of quantum systems. This tutorial provides a comprehensive introduction to the Berry phase, beginning with the essential mathematical framework required to grasp its significance. We explore the intrinsic link between the emergence of a non-trivial Berry phase and the presence of topological characteristics in quantum systems, showing the connection between the Berry phase and the band structure as well as the phase’s gauge-invariant nature during cyclic evolutions. The tutorial delves into various topological effects arising from the Berry phase, such as the quantum, anomalous, and spin Hall effects, which exemplify how these quantum phases manifest in observable phenomena. We then extend our discussion to cover the transport properties of topological insulators, elucidating their unique behaviour rooted in the Berry phase physics. This tutorial aims at equipping its readers with a robust understanding of the basic theory underlying the Berry phase and of its pivotal role in the realm of topological quantum phenomena.

The La_0.9·0.1MnO_2.9 compound were prepared by sol–gel method with the aim of obtaining a material with interesting magnetocaloric and thermoelectric properties. The prepared material crystallized in rhombohedric system with R-3c space group. In the magnetization vs. temperature graph, it is observed a paramagnetic (PM)-ferromagnetic (FM) transition with a Curie temperature T_C of 209 K. From the fit of hysteresis cycle at 5 K, it is observed that the dominant contribution is ferromagnetic. A magnetic entropy change, calculated from the isothermal magnetization curves, was observed for the sample with a peak centered on T_C. The total electronic density states (TDOS) show the coexistence of metallic behavior for spin-up states and semiconductor characteristic, with a Eg = 1.3 eV, for spin-down states. Thermoelectric properties analysis revealed promising behavior with ZT that assesses the efficacy of a compound in a thermoelectric field, reaching 1.1 at 420 K.

We report a study of a cavity optomechanical system driven by narrowband electromagnetic fields, which are applied either in the form of uncorrelated noise, or as a more structured spectrum. The bandwidth of the driving spectra is smaller than the mechanical resonant frequency, and thus we can describe the resulting physics using concepts familiar from regular cavity optomechanics in the resolved-sideband limit. With a blue-detuned noise driving, the noise-induced interaction leads to anti-damping of the mechanical oscillator, and a self-oscillation threshold at an average noise power that is comparable to that of a coherent driving tone. This process can be seen as noise-induced dynamical amplification of mechanical motion. However, when the noise bandwidth is reduced down to the order of the mechanical damping, we discover a large shift of the power threshold of self-oscillation. This is due to the oscillator adiabatically following the instantaneous noise profile. In addition to blue-detuned noise driving, we investigate narrowband driving consisting of two coherent drive tones nearby in frequency. Also in these cases, we observe deviations from a naive optomechanical description relying only on the tones’ frequencies and powers.

In this work, the magnetic and thermodynamic properties of dilute magnetic semiconductor quantum dots of cylindrical geometry are investigated. The eigenvalue of the quantum system we are considering is obtained by solving the one-electron Schrödinger equation within the framework of the effective mass approach. Then, taking into account the energy spectrum, expressions for thermodynamic quantities and magnetic susceptibility are obtained. The behavior of these expressions depending on temperature is studied using the parameters (B), (x), (R_{0}) and (L_{0}). Based on the results obtained, it is established that the average energy, free energy, heat capacity, entropy and magnetic susceptibility at low temperatures depend on the parameter (x). Also at low temperatures, when (x = 0), the average energy and free energy exhibit a linear relationship. With increasing temperature, this dependence becomes nonlinear. For (x ne 0), the dependence of the average energy and free energy on temperature is a rapidly increasing nonlinear function. In addition, when (x ne 0), magnetic susceptibility reaches a maximum at low temperatures. The peak height increases with (x) and disappears when (x = 0). The peak of magnetic susceptibility decreases as the magnetic field increases when (x ne 0) and shifts toward higher temperatures. The specific heat forms a Schottky peak at low temperatures and asymptotically approaches (C_{v} = 3k_{B}) at high temperatures.