Superconducting State Parameters of CucZr100-c Binary Amorphous Alloys by Pseudopotential Approach

We present the screening dependence theoretical investigations of the superconducting state parameters, i.e. electron-phonon coupling strength A, Coulomb pseudopotential μ＊, transition temperature To, isotope effect exponent α, and effective interaction strength NoV of some CucZr100-c （C = 25, 30, 33, 35, 40, 45, 50, 55, 57, 60 at.%） binary amorphous alloys by employing the well-known empty core model potential of Ashcroft. Five screening functions proposed by Hartree, Taylor, Ichimaru-Utsumi, Farid et al. and Sarkar et al. are used to study the screening influence on the aforesaid superconducting properties. The transition temperature Tc obtained from the Ichimaru-Utsumi screening function is found to be in excellent agreement with available theoretical or experimental data. Also, the present results are found in qualitative agreement with the other earlier reported data, which confirms the superconducting phase in the amorphous alloys.     

Semiclassical Theory of Quasiparticles in the Superconducting State

We have developed a semiclassical approach to solving the Bogoliubov-de Gennes equations for superconductors. It is based on the study of classical orbits governed by an effective Hamiltonian corresponding to the quasiparticles in the superconducting state and includes an account of the Bohr-Sommerfeld quantisation rule, the Maslov index, torus quantisation, topological phases arising from lines of phase singularities (vortices), and semiclassical wave functions for multidimensional systems. The method is illustrated by studying the problem of an SNS junction and a single vortex.     

Improved Superconducting Qubit State Readout by Path Interference

High fidelity single shot qubit state readout is essential for many quantum information processing protocols. In superconducting quantum circuit, the qubit state is usually determined by detecting the dispersive frequency shift of a microwave cavity from either transmission or reflection. We demonstrate the use of constructive interference between the transmitted and reflected signal to optimize the qubit state readout, with which we find a better resolved state discrimination and an improved qubit readout fidelity. As a simple and convenient approach, our scheme can be combined with other qubit readout methods based on the discrimination of cavity photon states to further improve the qubit state readout.     

Nucleation of Instability of the Meissner State of 3-Dimensional Superconductors

This paper concerns a nonlinear partial differential system in a 3-dimensional domain involving the operator curl², which is a simplified model used to examine nucleation of instability of the Meissner state of a superconductor as the applied magnetic field reaches the superheating field. We derive a priori C ^2+α estimates for a weak solution H, the curl of the magnetic potential, and determine the location of the maximal points of |curlH| which correspond to the nucleation of instability of the Meissner state. We show that, if the penetration length is small, the solution exhibits a boundary layer. If the applied magnetic field is homogeneous, |curlH| is maximal around the points on the boundary where the applied field is tangential to the surface.     

超导直线电机结构参数对性能影响

高温超导直线电机作为电磁弹射的动力核心,需要具备稳态推力大和推力稳定性高的特点.本文利用有限元仿真分析法,分析了定子背铁厚度、气隙长度、极矩以及超导磁体内径等结构参数对电机稳态推力、推力波动、气隙磁场垂直分量和铁心损耗的影响.由仿真数据得出：增大定子背铁厚度,铁心损耗有先增大后下降的变化趋势;极矩逐渐增大时,稳态推力先增大后减小,但是极矩的增大会带来电机推力波动的增大;增大超导磁体内径,电机稳态推力平均值升高.结果表明本次研究达到了增大推力以及提高推力稳定性的目的,并对后续超导直线电机结构优化提供了可靠依据.     

Quantum State Transfer with Tunable Couplings for Superconducting Qubits

Currently, scalability and decoherence are still the two crucial problems for realizing large-scale quantum computation. To transfer information efficiently in the field of quantum computer and quantum communication, we must solve the two problems reasonably. Here, we propose an efficient scheme for the implementation of quantum states transfer in different couplings of superconducting devices, which are coupled weakly over a long distance. It is found that the isotropic Heisenberg coupling can offer the perfect operation for arbitrary states transfer with the shortest time. The scheme is feasible because the couplings have been demonstrated in actual experiments recently.     

Low-Temperature Solid State Synthesis and Characterization of Superconducting Vanadium Nitride

Superconducting vanadium nitride(VN) is successfully synthesized by a solid-state reaction of vanadium pentoxide, sodium amide and sulfur in an autoclave at a relatively low temperature(240-400℃). The obtained samples are characterized by x-ray diffraction, x-ray photoelectron spectroscopy and transmission electron microscopy.The result of the magnetization of the obtained VN product as a function of temperature indicates that the onset superconducting transition temperature is about 8.4 K. Furthermore, the possible reaction mechanism is also discussed.     

The Thermodynamic Properties of Superconducting State in BZA Mean-Field Theory

The thermodynamic properties of superconducting state in BZA mean-field theory of RVB superconducting mechanism are evaluated in this letter.     

Structure and Parameters of Boundary Vortices in a Superconducting Josephson Medium

JETP Letters - The dynamics of the formation of different-scale vortices and antivortices in bulk and film YBa2Cu3O7–x samples in the process of their “decomposition” into twins...     

Another Possible Phenomenological Model of the Normal State of the High-Tc Oxide Superconductors

A new phenomenological model has been proposed to account for the anomalous normal state properties of the high-T_c, oxide superconductors. Comparison with the assumed one in the marginal Fermi liquid theory is made. Both of them are similar, but also different. It is shown that in a small frequency region of ω < T (T being the temperature), the conventional Fermi liquid picture still holds, while for ω > T the marginal Fermi liquid theory is appropriate.     

Observation of Two-Level Critical State in the Superconducting FeTe Thin Films

FeTe, a non-superconducting parent compound in the iron-chalcogenide family, becomes superconducting after annealing in oxygen. Under the presence of magnetism, spin-orbit coupling, inhomogeneity and lattice distortion,the nature of its superconductivity is not well understood. Here we combine the mutual inductance technique with magneto transport to study the magnetization and superconductivity of FeTe thin films. It is found that the films with the highest T_C show non-saturating superfluid density and a strong magnetic hysteresis distinct from that in a homogeneous superconductor. Such a hysteresis can be well explained by a two-level critical state model and suggests the importance of granularity to superconductivity in this compound.     

Superconducting State in the Lagrangian Formalism of the Generalized Hubbard Model

The nonperturbative large-N expansion applied to the generalized Hubbard model describing N-fold-degenerate correlated bands is considered. Our previous results, obtained in the framework of the Lagrangian formalism for the normal-state case, are extended to the superconducting state. The standard Feynman diagrammatics is obtained and the renormalized physical quantities are computed and analyzed. Our purpose is to obtain the 1/N corrections to the renormalized boson and fermion propagators when a state with Cooper-pair condensation (i.e., the superconducting state) is considered.     

高温超导脉冲变压器线圈结构参数影响分析

用于脉冲功率电源的高温超导脉冲变压器,集超导储能与脉冲放电为一体,在脉冲功率技术中有着良好的发展前景。设置合理的线圈结构参数可以提升高温超导脉冲功率变压器的耦合系数和储能容量,满足脉冲功率电源小型化、轻量化的优化目标。本文利用有限元仿真软件Anysys EM,建立了同轴饼式线圈叠加结构的单模块变压器模型和环形结构的多模块变压器模型,根据磁场分布和后期计算,分析了结构参数对脉冲变压器耦合系数和原边超导线圈的储能的影响。仿真分析结果表明,在77 K时,采用相同用线量的情况下,单模块高温超导脉冲变压器耦合系数和原边电感线圈的储能随线圈高度减小逐渐增大;多模块高温超导脉冲变压器减小线圈高度、增大内半径能够获得较高的性能,为超导脉冲变压器的脉冲电源实验验证提供了一定的参考依据。