New approach to theory of tunneling spectroscopy in unconventional superconductors

TL;DR

This paper introduces a new boundary condition approach based on tight-binding models for tunneling spectroscopy in unconventional and multiband superconductors, enabling more accurate analysis of complex spectra.

Contribution

It develops a generalized boundary condition framework beyond effective mass approximation for tunneling spectroscopy in complex superconductors.

Findings

Derived new boundary conditions for NS interfaces.

Applied model to pnictide junctions with different orientations.

Provided a basis for quantitative tunneling spectroscopy in multi-orbital superconductors.

Abstract

We have derived new boundary conditions on wave function at the normal metal / superconductor (NS) interface beyond effective mass approximation. These conditions are based on tight-binding approach and enable one to formulate quantitative model for tunneling spectroscopy of superconductors with complex non-parabolic energy spectra. The model is applied to superconductors with unconventional pairing and with multiband electronic structure. In the case of single band unconventional superconductors this model provides known conductance formula (Phys. Rev. Lett. 74 3451 1995), but with generalized definition of the normal-state conductance. Based on new boundary conditions, we have calculated conductance in normal metal / superconducting pnictide junctions for different orientations of the NS interface with respect to the crystallographic axes of the pnictides. The present approach provides the basis for quantitative tunneling spectroscopy in multi-orbital superconductors.