Journal of Low Temperature Physics最新文献

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.

In this paper, we investigate the interplay of Dzyaloshinskii–Moriya interaction (DMI) and uniform and staggered fields in x and z directions on entanglement in the spin-1/2 one-dimensional Heisenberg chain. We use the well-known mapping of this model on sine-Gordon theory to calculate the quantum entanglement quantifiers as von Neumann entropy and entanglement negativity, which provides a useful framework for studying the emergence of quantum correlation in this model. How the behavior of the spin velocity implies in a significant impact on energy of elementary excitations, carrying spin (S^z=pm 1/2), we get that the DMI interaction and external fields generate a large effect on behavior of the spinons energy and quantum correlation.

High-efficiency microcalorimeter arrays are required as imaging spectroscopy for X-ray microscopy in general and for astrophysics. We have developed in-house an array of Transition Edge Sensor (TES) X-ray microcalorimeters with mushroom-type absorbers which have a large area of (260,upmu hbox {m}) square with multiple support stems. Insufficient thermal conductivity may degrade the energy resolution. We construct a 3D FEM simulation with thermal conduction and electric feedback circuit of TES. Estimated physical parameters were incorporated into the simulation to reproduce the measured pulse waveforms. As a result, the effect of the large absorber on the degradation of energy resolution was small for the mushroom-type absorber TES calorimeter.

In this work, we propose a magnetic bolometer to be employed in the search of primordial B-modes in the CMB. These magnetic bolometers are an adaptation of the well-known metallic magnetic calorimeters used in particle physics. They rely on the magnetization dependence on temperature of alloys such as Au:Er and Ag:Er. In addition to the low intrinsic noise a magnetic bolometer of this nature offers, the broad and smooth temperature-dependent magnetization of metallic magnetic sensors ultimately translates to a high dynamic range and straightforward calibration. Their intrinsic noise equivalent power (NEP) is estimated to be in the range of 10–100 aW/(sqrt{(}text {Hz})). We outline here a workable design for such a detector utilizing an antenna-coupled approach and present the simulated power transfer ratio that was attained; the detector’s performance is discussed by combining this result with its responsivity.

The MIllimeter Sardinia radio Telescope Receiver based on Array of Lumped elements KIDs, MISTRAL, is a cryogenic LEKID camera, operating in the W band (({77}{-}{103,textrm{GHz}})) from the Gregorian focus of the 64-m aperture Sardinia Radio Telescope (SRT), in Italy. This instrument features a high angular resolution ((sim {12,textrm{arcsec}})) and a wide instantaneous field of view ((sim {4,textrm{arcmin}})), allowing continuum surveys of the mm-wave sky with many scientific targets, including observations of galaxy clusters via the Sunyaev–Zel’dovich effect. In May 2023, MISTRAL has been installed at SRT for the technical commissioning. In this contribution, we will describe the MISTRAL instrument focusing on the laboratory characterization of its focal plane: a (sim {400})-pixel LEKID array. We will show the optical performance of the detectors highlighting the procedure for the identification of the pixels on the focal plane, the measurements of the optical responsivity and NEP, and the estimation of the optical efficiency.