Searching strong ‘spin’-orbit coupled one-dimensional hole gas in strong magnetic fields

We show that a strong `spin'-orbit coupled one-dimensional (1D) hole gas is achievable via applying a strong magnetic field to the original two-fold degenerate (spin degeneracy) hole gas confined in a cylindrical Ge nanowire. Both strong longitudinal and strong transverse magnetic fields are feasible to achieve this goal. Based on quasi-degenerate perturbation calculations, we show the induced low-energy subband dispersion of the hole gas can be written as $E=\hbar^{2}k^{2}_{z}/(2m^{*}_{h})+\alpha\sigma^{z}k_{z}+g^{*}_{h}\mu_{B}B\sigma^{x}/2$, a form exactly the same as that of the electron gas in the conduction band. Here the Pauli matrices $\sigma^{z,x}$ represent a pseudo spin (or `spin' ), because the real spin degree of freedom has been split off from the subband dispersions by the strong magnetic field. Also, for a moderate nanowire radius $R=10$ nm, the induced effective hole mass $m^{*}_{h}$ ($0.065\sim0.08~m_{e}$) and the `spin'-orbit coupling $\alpha$ ($0.35\sim0.8$ eV~\AA) have a small magnetic field dependence in the studied magnetic field interval $1<B<15$ T, while the effective $g$-factor $g^{*}_{h}$ of the hole `spin' only has a small magnetic field dependence in the large field region.

Effective Magnetic Field Dependence of the Flux Pinning Energy in FeSe0.5Te0.5 Superconductor

The role of a layered structure in superconducting pinning properties is still at a debate. The effects of the vortex shape, which can assume for example a staircase form, could influence the interplay with extrinsic pinning coming from the specific defects of the material, thus inducing an effective magnetic field dependence. To enlighten this role, we analysed the angular dependence of flux pinning energy U(H,θ) as a function of magnetic field in FeSe0.5Te0.5 thin film by considering the field components along the ab-plane of the crystal structure and the c-axis direction. U(H,θ) has been evaluated from magneto-resistivity measurements acquired at different orientations between the applied field up to 16 T and FeSe0.5Te0.5 thin films grown on a CaF2 substrate. We observed that the U(H,θ) shows an anisotropic trend as a function of both the intensity and the direction of the applied field. Such a behaviour can be correlated to the presence of extended defects elongated in the ab-planes, thus mimicking a layered superconductor, as we observed in the microstructure of the compound. The comparison of FeSe0.5Te0.5 with other superconducting materials provides a more general understanding on the flux pinning energy in layered superconductors.

Nontopological zero-bias peaks in full-shell nanowires induced by flux-tunable Andreev states

A semiconducting nanowire fully wrapped by a superconducting shell has been proposed as a platform for obtaining Majorana modes at small magnetic fields. In this study, we demonstrate that the appearance of subgap states in such structures is actually governed by the junction region in tunneling spectroscopy measurements and not the full-shell nanowire itself. Short tunneling regions never show subgap states, whereas longer junctions always do. This can be understood in terms of quantum dots forming in the junction and hosting Andreev levels in the Yu-Shiba-Rusinov regime. The intricate magnetic field dependence of the Andreev levels, through both the Zeeman and Little-Parks effects, may result in robust zero-bias peaks—features that could be easily misinterpreted as originating from Majorana zero modes but are unrelated to topological superconductivity.

Maxwell quasi-variational inequalities in superconductivity

This paper is devoted to the mathematical modeling and analysis of a hyperbolic Maxwell quasi-variational inequality (QVI) for the Bean-Kim superconductivity model with temperature and magnetic field dependence in the critical current. Emerging from the Euler time discretization, we analyze the corresponding H(curl)-elliptic QVI and prove its existence using a fixed-point argument in combination with techniques from variational inequalities and Maxwell's equations. Based on the existence result for the H(curl)-elliptic QVI, we examine the stability and convergence of the Euler scheme, which serve as our fundament for the well-posedness of the governing hyperbolic Maxwell QVI.