Current-Voltage Relations in d-wave Josephson Junctions: Effects of Midgap Interface States

TL;DR

This paper analyzes how midgap interface states in d-wave Josephson junctions alter the current-voltage characteristics, especially the subharmonic gap structure, and explains the physical processes behind these effects.

Contribution

It provides a detailed theoretical analysis of the impact of midgap states on the I-V characteristics of d-wave Josephson junctions, including the effects of interface broadening.

Findings

Midgap states significantly modify the subharmonic gap structure.

Resonances in n-particle processes are altered by midgap states.

MGS can produce a zero-bias current peak.

Abstract

We investigate the dc current-voltage characteristics of d-wave Josephson junctions, where the barrier at the interface may have arbitrary strength. Dividing the current into n-particle currents $I_n$ (n integer), we can explicitly show which physical processes are responsible for the subharmonic gap structure (SGS). For orientations where midgap states (MGS) exist, the resonances in the n-particle processes are drastically changed, giving rise to a strongly modified SGS. Introducing broadening in a phenomenological way, we show that MGS may produce a current peak near zero bias and we explain which physical processes are contributing to this peak. The agreement of our theory with recent experiments is discussed.