Directional tunnelling spectroscopy of a normal metal-$s+g$-wave superconductor junction

TL;DR

This paper calculates tunnelling spectra for a normal metal-$s+g$-wave superconductor junction, revealing orientation-dependent features and differences between point and line node gap structures, relevant to borocarbide superconductors.

Contribution

It provides detailed theoretical tunnelling spectra for $s+g$-wave superconductors with different nodal structures and orientations, enhancing understanding of their gap symmetries.

Findings

Spectra depend strongly on junction orientation.

Two prominent peaks appear at energies related to the gap function.

Distinct spectral features differentiate point and line node gaps.

Abstract

We calculate the normal metal-$s+g$-wave superconductor tunnelling spectrum for various junction orientations and for two forms of the superconducting gap, one which allows for point nodes and the other which allows for line nodes. For a junction oriented with its normal parallel to the ab plane of the tetragonal superconductor, we find that the tunnelling spectrum is strongly dependent on orientation in the plane. The spectrum contains two peaks at energies equivalent to the magnitudes of the gap function in the direction parallel to the interface normal and in the direction making a $\pi/4$ angle with the normal. These two peaks appear in both superconductors with point nodes and line nodes, but are more prominent in the latter. For the tunnelling along the c axis, we find a sharp peak at the gap maximum in the conductance spectrum of the superconductor with line nodes, whereas with point nodes we find a peak occurring at the value of the gap function along the c axis. We discuss the relevance of our result to borocarbide systems.