BCS theory for s+g-wave superconductivity borocarbides Y(Lu)Ni$_2$B$_2$C

TL;DR

This paper develops a BCS theoretical model for s+g-wave superconductivity in borocarbides, confirming the stability of mixed pairing states with point nodes, aligning with experimental observations.

Contribution

It introduces a semi-phenomenological BCS framework for s+g-wave pairing, demonstrating the stability of mixed s- and g-wave states in borocarbides.

Findings

Stable coexistence of s- and g-wave components confirmed.

Equal s and g amplitudes (x=1/2) can be stable.

The model explains point nodes observed experimentally.

Abstract

The s+g mixed gap function \Delta_k=\Delta {[(1-x)-x\sin^4\theta\cos4\phi]} (x: weight of g-wave component) has been studied within BCS theory. By suitable consideration of the pairing interaction, we have confirmed that the coexistence of s- and g-wave, as well as the state with equal s and g amplitudes (i.e., x=1/2) may be stable. This provides the semi-phenomenological theory for the s+g-wave superconductivity with point nodes which has been observed experimentally in borocarbides YNi_2B_2C and possibly in LuNi_2B_2C.