Subharmonic gap structure in d-wave superconductors

TL;DR

This paper develops a self-consistent theory for the current-voltage characteristics of d-wave/d-wave superconducting contacts, revealing conditions for subharmonic gap structure observation and its unique features in cuprate junctions.

Contribution

It provides the first comprehensive analysis of subharmonic gap structure in d-wave superconductors, including effects of bound states, scattering, and magnetic fields.

Findings

SGS is possible in d-wave superconductors

Bound states cause an even-odd effect in SGS

Magnetic fields cause a distinctive splitting of SGS

Abstract

We present a self-consistent theory of current-voltage characteristics of d-wave/d-wave contacts at arbitrary transparency. In particular, we address the open problem of the observation of subharmonic gap structure (SGS) in cuprate junctions. Our analysis shows that: (i) the SGS is possible in d-wave superconductors, (ii) the existence of bound states within the gap results in an even-odd effect in the SGS, (iii) elastic scattering mechanisms, like impurities or surface roughness, may suppress the SGS, and (iv) in the presence of a magnetic field the Doppler shift of the Andreev bound states leads to a very peculiar splitting of the SGS, which is an unambiguous fingerprint of d-wave superconductivity.