Physica C-superconductivity and Its Applications最新文献

This study applies the time-dependent Ginzburg–Landau (TDGL) theory with thermal noise to analyze the thermoelectric and transport properties of superconducting Sn nanowires, focusing on the thermopower (${\alpha }_{xx}$) and the phase transition characteristics in the S-shaped $J$-$E$ curves. We observe significant contributions from superconducting Cooper pairs, which remain nonzero above the critical temperature ($T_c$), indicating residual superconductivity due to strong thermal fluctuations. The S-like shape in the $J$-$E$ curves is attributed to a dynamical instability transition temperature ($T^{\ast }$) at approximately 2.9 K, where thermal fluctuations dominate. Furthermore, we compare the resistance in the linear response to experimental data for Sn nanowires both below and above $T_c$. Below $T_c$, the resistance sharply decreases, reflecting the robust superconducting state, while above $T_c$, it increases, aligning with normal state behavior. In nonlinear response case, our results indicate that high electric fields can be effectively used to suppress order-parameter fluctuations and the electrical conductivity in superconducting nanowires. The findings provide critical insights into the thermoelectric behavior and phase transitions in Sn nanowires, highlighting the importance of Cooper pair dynamics in shaping the transport properties of one-dimensional superconductors. This understanding is essential for the development of advanced nanoelectronic devices leveraging these unique superconducting properties.

In this paper, the effect of non-uniform critical current density on bulk superconductors is studied, the case of a long cylindrical superconductor with transport current is chose to discussed. The critical current density is distributed non-uniformly along the radius of the cylinder. Based on the Bean critical state model, the distributions of trapped magnetic flux and shielding current in the cylinder are investigated. Combined with the plane strain approach, the analytical expressions of magnetic flux pinning force and stress are obtained. The magnetostriction of the cylinder is also discussed. Results show that the non-uniform critical current density changes the distribution law of the shielding current and trapped magnetic flux in the cylinder. The increase of non-uniform parameters n leads to an obvious increase in the flux pinning force. Thus, a larger extreme value of the pinning stress is obtained, a bigger structure deformation is produced inside the superconducting cylinder. All those conclusions will provide a helpful guide for engineering application.

The development of superconductor integrated circuits (SCIC) places increasing demands on electronic design automation (EDA) tools. Circuit simulation is a crucial step in the design process of superconducting quantum interference devices (SQUID) and single flux quantum (SFQ) circuits. Over the years, there have been many SC circuit simulators, like JSPICE, JSIM, WRspice, JoSIM, PSCAN2, JSICsim, PrimeSim HSPICE, Spectre, and more. The previous studies have compared the differences in results among some simulators for the same circuit cases. However, designers of SC circuits still face challenges when choosing simulators and setting simulation parameters. The performance of these simulators lacks comprehensive and quantitative evaluations to date. To evaluate the performance of the simulators, we focused on three aspects: the differences among the IV results, accuracy, and speed. For characterizing the accuracy of the simulators, we proposed a method that uses the relative error between the numerical and analytical solutions at the $L$-$C$ resonance point on the IV curve of a dc SQUID. In this article, we have selected five representative simulators JoSIM, JSIM, WRspice, PSCAN2, and JSICsim for our study. By using multiple cases of the bare and coupled dc SQUID, multiple IV curves, and the analytical solution as a reference, we comprehensively compared the performance of these simulators. Additionally, we quantitatively examined the impact of two key simulation parameters, namely, the maximum allowed simulation timestep (max timestep) and relative tolerance (RelTol), on the performance of these simulators. Our results show that the normalized voltage differences in the IV curves of different simulators are relatively small (within 0.06) in regions far from the $L$-$C$ resonance point, while they increase significantly near the $L$-$C$ resonance point (maximum is 0.4). PSCAN2 exhibits a significant relative error of approximately 16% when the max timestep is 0.6ps and RelTol is $1\times 10^{-1}$, which is close to its default RelTol value. Our work provides some insights and references for the designers of SC circuits on how to choose simulators and set simulation parameters.

We show that formation of Zhang-Rice singlets (ZRS) naturally explains the empirical superconducting dome by random distribution of holes in copper-oxygen plane of cuprates. A general relation T_c/T_cmax=25(c-0.04), where c is the concentration of the ZRS and T_cmax is the maximum of critical temperature T_c, is obtained and reproduces the doping-dependent critical temperature evolution in the whole superconducting dome. The relation has been applied to estimate the effects of impurities substituting copper in the copper-oxygen plane. Our relation successfully predicts the suppression of superconductivity due to the substitution of Cu by the impurities. We demonstrate that T_c decreases linearly with the increase of the impurity concentration and the scattering range plays a key role in the suppression of the superconductivity. These results agree well with the experimental observations of the substitutions by Zinc and Nickel. Our relation is universal for all families of cuprates and explains the formation of the superconducting dome in the phase diagram.

This paper presents a design for five conventional superconducting magnet structures to meet the high magnetic load demand of superconducting motors while reducing the superconducting tapes consumption. A 45° highest efficiency line is proposed based on the graphical method, and the magnet structure is optimized by combining finite element and PSO algorithms. Additionally, a correlation function is established using the vertical magnetic field to estimate the critical current, describing the nonlinear relationship between the two. The optimization method can maintain the airgap flux density waveform before and after optimization, reduce tapes consumption and perpendicular field on the tapes, refine the field distribution, and improve the safety margin of superconducting coils. The magnet design scheme can be selected with low tape consumption or high safety margin according to actual demand. This research can be used to optimize the electromagnetic design of superconducting electric motors, as well as other superconducting magnet applications, such as superconducting magnetic bearings, nuclear magnetic resonance, and large-scale scientific installations for high-energy physics. The aim is to achieve the exhaustive use of superconducting tapes.

Rapid Single Flux Quantum (RSFQ) circuits are promising for energy-efficient and high-frequency digital applications. Energy consumption could be reduced effectively when RSFQ circuits operate at higher temperatures. We developed a fabrication process for all-NbN RSFQ circuits based on NbN/AlN/NbN Josephson junctions on single-crystal MgO substrates with the NbN ground layer on the top. The electrical properties of NbN junctions and NbN inductance were measured in the temperature range from 4.2 to 14 K. The NbN junction parameters decreased with an increase in temperature. The value of NbN inductance increased with an increase in temperature. The all-NbN Josephson Transmission Line (JTL) was designed, fabricated, and tested in the temperature range of 10 K. The result showed that the NbN-based JTL can work stable at 10 K. The margins were measured near 10 K.

The influence of annealing treatments on the crystal structure and superconducting properties of polycrystalline YBa₂Cu_3-xFe_xO_7-δ has been estimated. The Fe elements was doped into Cu sites in polycrystalline YBa₂Cu_3-xFe_xO_7-δ for 0.0 ≤ x ≤ 0.4. All of samples were annealed under different atmospheres: a low-oxygen-pressure atmosphere in flowing oxygen and a high-oxygen-pressure ambient. The local structure, magnetization, and electrical transport properties have been compared for the two series of samples before and after annealing. The lattice constants and T_c have been shown as a function of iron concentration for samples, indicating that the polycrystalline YBa₂Cu_3-xFe_xO_7-δ materials display a structural transition from orthorhombic to tetragonal phase with increasing Fe concentration. Compared to as-synthesized samples, the annealed samples achieve a higher T_c. Furthermore, the YBa₂Cu_3-xFe_xO_7-δ samples with x = 0.2, 0.3, 0.4 undergo from non-superconducting state to superconducting state after annealing.