Comment on ``Electrical Transport in Junctions between Unconventional Superconductors: Application of the Green Function Formalism''

TL;DR

This paper emphasizes the importance of surface pair breaking effects in unconventional superconductor junctions, highlighting their impact on bound states and tunneling characteristics, which were previously neglected in theoretical models.

Contribution

It critiques prior approaches for ignoring surface pair breaking and demonstrates the significant influence of these effects on bound states and Josephson current in unconventional superconductor junctions.

Findings

Surface pair breaking significantly affects bound states.

Midgap states influence current-voltage characteristics.

Orientation dependence impacts Josephson critical current.

Abstract

Effect of surface pair breaking, entirely neglected by M. Samanta and S. Datta [Phys. Rev. B v. 57, 10972 (1998)], is quite important in considering surface (or interface) quasiparticle bound states and associated characteristics of junctions involving unconventional superconductors. The whole class of bound states with nonzero energy is simply omitted within the framework of the approach, using uniform spatial profile of the order parameter up to the interface. The contribution of these bound states (as well as midgap states) to current-voltage characteristics of the SIS' tunnel junctions were studied for the first time in our earlier article. Dependence of midgap state contribution to the Josephson critical current upon crystal to interface orientations is shown as well to be fairly sensitive to the effect of surface pair breaking.