Effect of diffusive boundaries on surface superconductivity in unconventional superconductors

TL;DR

This paper derives boundary conditions for superconducting order parameters at diffusive boundaries and shows that surface superconductivity is suppressed in anisotropic superconductors unless the surface is along high symmetry directions.

Contribution

It provides a microscopic derivation of boundary conditions and demonstrates the suppression of surface superconductivity in anisotropic materials due to diffusive boundaries.

Findings

Diffusive boundaries suppress surface superconductivity in anisotropic superconductors.

Surface superconductivity is only observable along high symmetry directions.

Boundary conditions are derived from microscopic theory for the order parameter.

Abstract

Boundary conditions for a superconducting order parameter at a diffusive scattering boundary are derived from microscopic theory. The results indicate that for all but isotropic gap functions the diffusive boundary almost completely suppresses surface superconductivity in the Ginzburg-Landau regime. This indicates that in anisotropic superconductors surface superconductivity can only be observed for surface normals along high symmetry directions where atomically clean surfaces can be cleaved.