Impurity effects on s+g-wave superconductivity in borocarbides Y(Lu)Ni_2B_2C

TL;DR

This paper investigates how impurities affect the s+g-wave superconductivity in borocarbides YNi2B2C and LuNi2B2C, showing impurity scattering suppresses nodal excitations and induces a finite energy gap, aligning with experimental observations.

Contribution

It provides a detailed analysis of impurity effects on s+g-wave superconductivity, including quasiparticle states and thermodynamics, which was not previously explored.

Findings

Impurity scattering suppresses nodal excitations in s+g-wave superconductors.

A finite energy gap rapidly develops with increasing impurity scattering.

Results qualitatively match experimental specific heat behavior.

Abstract

Recently a hybrid s+g-wave pairing is proposed to describe the experimental observation for a nodal structure of the superconducting gap in borocarbide YNi$_2$B$_2$C and possibly LuNi$_2$B$_2$C. In this paper the impurity effects on the s+g-wave superconductivity are studied in both Born and unitarity limit. The quasiparticle density of states and thermodynamics are calculated. It is found that the nodal excitations in the clean system are immediately prohibited by impurity scattering and a finite energy gap increases quickly with the impurity scattering rate. This leads to an activated behavior in the temperature dependence of the specific heat. Qualitative agreement with the experimental results is shown. Comparison with d-wave and some anisotropic s-wave studied previously is also made.