In-gap bound states and tunneling conductance of multiband superconductors through a normal/superconductor/superconductor junction

TL;DR

This paper investigates tunneling conductance in a multiband superconductor junction with a normal metal and a single-band superconductor layer, revealing in-gap bound states linked to phase frustration, aiding gap symmetry identification.

Contribution

It introduces a model for tunneling conductance in multiband superconductor junctions and identifies in-gap bound states caused by phase frustration.

Findings

In-gap conductance peaks due to bound states

Phase frustration leads to in-gap states

Implications for iron-based superconductor gap symmetry

Abstract

The tunneling conductance between a metal and a multiband s-wave superconductor with a thin layer of single-band s-wave superconductor sandwiched in between is examined in this paper. We show that an in-gap peak in conductance curve is found as a result of the formation of in-gap bound state between the single-band and multiband superconductor junctions if the phases of the superconducting order parameters of the multiband superconductor are frustrated. The implication of this result in determining the gap symmetry of the iron-based superconductors is discussed.