Pairing of j=3/2 fermions in half-Heusler superconductors

TL;DR

This paper explores how j=3/2 fermion pairing in half-Heusler superconductors leads to unconventional states with topologically nontrivial nodes, expanding understanding beyond traditional pairing theories.

Contribution

It introduces a theoretical framework for j=3/2 fermion pairing in half-Heusler superconductors, revealing novel quintet and septet pairing states with topological features.

Findings

Identification of s-wave quintet states with topological nodes

Prediction of mixed s-wave singlet and p-wave septet states due to broken inversion symmetry

Revelation that local s-wave pairs manifest as d-wave states in momentum space

Abstract

We theoretically consider the superconductivity of the topological half-Heusler semimetals YPtBi and LuPtBi. We show that pairing occurs between j=3/2 fermion states, which leads to qualitative differences from the conventional theory of pairing between j=1/2 states. In particular, this permits Cooper pairs with quintet or septet total angular momentum, in addition to the usual singlet and triplet states. Purely on-site interactions can generate s-wave quintet time-reversal symmetry-breaking states with topologically nontrivial point or line nodes. These local s-wave quintet pairs reveal themselves as d-wave states in momentum space. Furthermore, due to the broken inversion symmetry in these materials, the s-wave singlet state can mix with a p-wave septet state, again with topologically-stable line nodes. Our analysis lays the foundation for understanding the unconventional superconductivity of the half-Heuslers.