Journal of Low Temperature Physics最新文献

The temperature dependence of the chemical potential in a half-filled Landau subband of a two-dimensional electron gas (2DEG), modeled using a Gaussian density of states (DOS), has been investigated through detailed numerical simulations. A characteristic temperature interval (0-{T}^{*}) is identified, within which the chemical potential remains nearly constant and close to the Fermi energy ({E}_{F}). The variation of ({T}^{*}) with the effective mass, filling factor, and broadening parameter (Gamma) is systematically analyzed. Temperature-dependent filling factors of Landau levels are also calculated, clarifying the mechanism by which asymmetric inter-subband transitions drive the deviation of (mu) from ({E}_{F}). The results show good agreement with available experimental data for 2DEG systems and provide a solid theoretical basis for interpreting magnetization, entropy, and heat capacity measurements in quantizing magnetic fields. These findings deepen the understanding of the thermodynamics of quantized states in two-dimensional electron gases and underlines their significance for contemporary low-temperature physics.

We present a simulation framework for the electro-thermal modeling of AlMn transition-edge sensors (TESs) with large-area absorbers, which are essential for the Wide-band X-ray Polarization Telescope (WXPT) to achieve high quantum efficiency across the 3–60 keV science band. The framework incorporates the two-fluid model for the superconducting transition and a dedicated thermal model for the (textrm{SiN}_{textrm{x}}) membrane. After experimental validation, the model is applied to quantify position-dependent energy broadening. We implemented an efficient sparse-sampling strategy to map the spatial response. Under a fixed heat-capacity budget, the position-induced broadening is contained below (6.97 textrm{eV}) @ (59.5 textrm{keV}). This result is achieved for absorbers with a side length of (sim 1 textrm{mm}) and supporting pillar widths under (50 upmu textrm{m}), further confirming the design’s effectiveness. This work provides a predictive simulation tool and concrete geometrical constraints to guide the design of the WXPT focal-plane array.

The present theoretical analysis is carried out in order to study some aspects of the electron transport in a degenerate two-dimensional electron gas (2DEG) at low lattice temperature, taking into account some particular features. These features, in contrast to the usual practice, include the inelasticity of the interaction of the carriers with the intravalley acoustic phonons, the true phonon distribution function setting aside the equipartition approximation for the same, and the transverse component of the three-dimensional phonon wave vector in the light of Ridley’s momentum conservation approximation. The scattering rate and the corresponding zero-field mobility are evaluated for an ensemble of degenerate carriers, confined in a triangular quantum well at the AlGaAs/GaAs interface, over a range of the lattice temperatures and the degeneracy levels. Numerical results demonstrate that the degeneracy parameter, the inelastic electron–phonon interaction, and the transverse component of phonon wave vector contribute significantly to effect the scattering and mobility characteristics compared to traditional theories, particularly in the low-temperature regime. The results which are obtained here seem to be stimulating and thus call forth more studies in the same framework as that of the present analysis.

It has been shown that a chain of unusual vortices can travel in a Josephson sandwich embedded in a dielectric. The limiting velocity of such vortex chain is greater than the limiting velocity of the usual vortex chain by (coth (L/lambda )), where L is the thickness of the sandwich electrodes, (lambda) is the London penetration depth. This makes it much easier to extract radiation into a dielectric, in which the speed of light (c_m) must be less than the velocity of the vortex chain v. Cherenkov radiation from a chain of unusual vortices in the dielectric surrounding the sandwich has been studied. The radiation spectrum of the chain consists of a discrete number of lines at frequencies that are multiples of (2pi v/Xi), where (Xi) is the period of the chain. In cases where (Xi) is of the order of the size of a solitary vortex or greater, then the main contribution to the radiation occurs at the frequency of the first harmonic. For typical parameters of the sandwich and the chain, the radiation frequency falls in the terahertz range.

The paper presents the theory of planar ballistic SNS junctions with equal Fermi velocities and effective masses in all layers. The theory takes into account phase gradients in superconducting layers commonly ignored in the past. At (T=0), the current-phase relation was derived for any thickness L of the normal layer in the model of the steplike pairing potential model analytically. The obtained current-phase relation is essentially different from that in theory neglecting phase gradients, especially in the limit (Lrightarrow 0) (short junction). The analysis resolves the problem with the charge conservation law in the steplike pairing potential model. The current-phase relation at temperatures exceeding the energy spacing between Andreev levels but less than the critical temperature was also calculated numerically. The current at these temperatures is temperature independent and decreases with growing L as (1/L^4). The previous theory predicted the current exponentially decreasing with growing T and L. Possible implications of the analysis for planar junctions with non-equal Fermi velocities and for non-planar junctions (narrow normal bridge between two bulk superconductors) are also discussed.

Layered transition metal dichalcogenides, such as MoS₂, are promising platforms for exploring electric-field-controlled phenomena. While gate-induced superconductivity has been extensively studied in single-crystalline MoS₂ flakes, the behavior of bulk polycrystalline MoS₂ under similar conditions remains unexplored. In this study, we investigate electric-field-induced phase transitions in bulk polycrystalline MoS₂ using an ionic liquid (IL) gate, focusing on the role of electrode configuration and contact proximity in transport properties, and on the emergence of superconductivity in bulk samples. Three different electrode configurations were employed to examine the impact of contact geometry. In setups with distant contacts, the samples exhibited insulating behavior down to 1.8 K, whereas in the configuration with contacts placed close to the gate electrode, a clear metal–insulator transition and the onset of superconductivity were observed, with a maximum T_c of 4.2 K. Analysis revealed that the contact resistance strongly depends on the distance between the gate electrode and the voltage/current leads, differing by nearly an order of magnitude between contacts located near and far from the gate. The critical apparent sheet resistance at the metal–insulator transition was estimated to be ~ 50 Ω, much lower than the quantum resistance, likely due to penetration of the IL into the granular polycrystalline structure. These findings highlight the crucial role of electrode configuration in IL gating of bulk materials and demonstrate that electrostatic doping can induce superconductivity in polycrystalline systems, extending the scope of gate-controlled quantum phenomena to materials for which high-quality single crystals are difficult to obtain.

In photonic quantum computing and quantum information processing, photon number resolution is crucial for generating highly non-classical quantum states. Superconducting transition-edge sensors (TESs) are considered one of the most effective photon number-resolving detectors for this purpose. However, the current timing properties of TESs, such as timing jitter (a few ns) and recovery time (several hundred ns), are insufficient, limiting the operational speed of quantum applications. To address the potential for improving TES timing performance, we have proposed an improved calculation to derive TES timing jitter. Our calculations including the effect of the SQUID noise indicate that expanding the electrical bandwidth of the external voltage amplifier and optimizing the inductance to match that bandwidth, can significantly improve timing jitter. According to our model, timing jitter 1 ns FWHM is achievable with an input inductance of 0.35 nH and an electrical bandwidth of 1 GHz. Additionally, we have shown that with our TES and SQUID parameters, the lowest achievable timing jitter is approximately 0.71 ns FWHM. Achieving an even lower jitter would require a redesign aimed at further reducing the SQUID noise.

Using Gross–Pitaevskii theory within the double-parabola approximation framework, we investigate wetting phase transitions in three-component Bose–Einstein condensates. A comprehensive mathematical framework is developed for interfacial phenomena, including explicit expressions for interfacial tensions, binding potentials, and phase transition criteria. Our analysis reveals both critical and first-order wetting transitions, with tricritical points where transition lines intersect. Detailed phase diagrams are constructed in immiscibility parameter space, and precise conditions for complete versus partial wetting are identified. Theoretical predictions are supported by numerical Gross–Pitaevskii solutions and provide specific guidance for experimental verification in ultracold atomic gases. The work addresses fundamental aspects of multicomponent wetting phenomena and establishes theoretical foundations for quantum phase transition studies.

Transition edge sensors (TESs) have emerged as highly sensitive radiation detectors with applications ranging from astrophysics to materials science. In the framework of the Athena X-ray space telescope, we have developed Mo/Au-based TES devices designed to meet the ESA specifications for the X-IFU instrument. The detectors were fabricated using a Mo/Au/Au trilayer process and characterized in a dilution refrigerator using a SQUID readout. From I to V curves and complex impedance measurements, we extracted the electrothermal parameters of the TES, which are consistent with theoretical models. Noise spectra were analyzed to estimate the energy resolution, and an excess noise factor was obtained from the comparison of theoretical and experimental data. A spectral resolution below 4 eV was achieved for 5.9 keV X-rays from a ⁵⁵Fe source.

We study an ideal Bose gas confined by a D-dimensional power-law potential within the framework of the Dunkl formalism. By analyzing the combined effects of spatial dimensionality and trap geometry, we derive universal expressions for the thermodynamic quantities, which depend solely on a single parameter. This reduction reveals the existence of universality classes that apply to any power-law potential, regardless of its specific form. Furthermore, we demonstrate that the thermodynamic consistency of the Dunkl formalism requires the Wigner parameter to lie within the interval [0, 2]. This finding extends previous results obtained for harmonically trapped ideal Bose gases and establishes that these bounds hold for arbitrary regular potentials in any dimension.