Surface Bound States in n-band Systems with Quasiclassical Approach

TL;DR

This paper extends the quasiclassical approach to analyze surface bound states in multi-band superconductors, revealing how normal state properties influence tunneling spectroscopy features like zero-bias conductance peaks.

Contribution

It generalizes the single-band method to n-band systems and clarifies the dependence of surface states on normal state properties rather than pair-potential anisotropy.

Findings

Zero-bias conductance peak depends on normal state properties in fully-gapped superconductors.

Surface density of states in two-band superconductors is calculated.

Surface-angular dependence of tunneling spectroscopy can be readily obtained.

Abstract

We discuss the tunneling spectroscopy at a surface in multi-band systems such as Fe-based superconductors with the use of the quasiclassical approach. We extend the single-band method by Matsumoto and Shiba [J. Phys. Soc. Jpn. 64, 1703 (1995)] into $n$-band systems ($n \geq 2$). We show that the appearance condition of the zero-bias conductance peak does not depend on details of the pair-potential anisotropy, but it depends on details of the normal state properties in the case of fully-gapped superconductors. The surface density of states in a two-band superconductor is presented as a simplest application. The quasiclassical approach enables us to calculate readily the surface-angular dependence of the tunneling spectroscopy.