Signature of superconducting states in cubic crystal without inversion symmetry

TL;DR

This paper theoretically investigates how the absence of inversion symmetry in cubic superconductors influences their pairing states, leading to unique magnetic and supercurrent phenomena that serve as signatures of broken symmetry.

Contribution

It introduces a model with isotropic spin-orbit interaction in noncentrosymmetric cubic superconductors and explores the resulting effects on pairing, supercurrents, and magnetic field distribution.

Findings

Induced supercurrent $f{J}$ and magnetization $f{M}$ are affected by broken inversion symmetry.

Magnetic fields perpendicular to external fields emerge as signatures of noncentrosymmetry.

The model predicts observable effects in magnetic field distribution in vortex and Meissner states.

Abstract

The effects of absence of inversion symmetry on superconducting states are investigated theoretically. In particular we focus on the noncentrosymmetric compounds which have the cubic symmetry $O$ like Li$_2$Pt$_3$B. An appropriate and isotropic spin-orbital interaction is added in the Hamiltonian and it acts like a magnetic monopole in the momentum space. The consequent pairing wavefunction has an additional triplet component in the pseudospin space, and a Zeeman magnetic field $\bf{B}$ can induce a collinear supercurrent $\bf{J}$ with a coefficient $\kappa(T)$. The effects of anisotropy embedded in the cubic symmetry and the nodal superconducting gap function on $\kappa(T)$ are also considered. From the macroscopic perspectives, the pair of mutually induced $\bf{J}$ and magnetization ${\bf{M}}$ can affect the distribution of magnetic field in such noncentrosymmetric superconductors, which is studied through solving the Maxwell equation in the Meissner geometry as well as the case of a single vortex line. In both cases, magnetic fields perpendicular to the external ones emerge as a signature of the broken symmetry.