Theory of tunnelling into a multi-band superconductor: decoherence and interference

TL;DR

This paper develops an exact Green's function approach to tunnelling in multi-band superconductors, revealing interference and decoherence effects that depend on pairing symmetry and Fermi velocities, aiding experimental identification of superconducting gap properties.

Contribution

It introduces a novel theoretical framework for tunnelling in multi-band superconductors, highlighting interference and decoherence effects influenced by pairing symmetry and Fermi velocities.

Findings

Interference effects depend on the sign of the superconducting gaps.

Decoherence effects influence Andreev reflections in tunnelling.

Experimental probes can determine pairing symmetry and gap signs.

Abstract

By an exact formulation of tunnelling into a multi-band superconductor in terms of Green's functions, we demonstrate that the multi-band feature of the iron-based superconductors can lead to novel interference between Andreev reflections and decoherence effect of quasi-particles to Andreev reflections in a tunnelling junction. These effects depend on the relative sign of the gaps for s-wave pairing, and the sign of the Fermi velocities also matters for tunnelling along the nodal direction of d-wave gaps. Experimental probe of such effects could determine both the pairing symmetry and the relative sign of the gaps on different bands.