Tuning the Parity Mixing of Singlet-Septet Pairing in a Half-Heusler Superconductor

TL;DR

This paper investigates the unconventional superconducting pairing in half-Heusler LuPdBi, demonstrating that electron irradiation can tune the ratio of singlet and septet pairing components, affecting the superconducting gap structure.

Contribution

It provides the first evidence that the parity mixing ratio in half-Heusler superconductors can be controlled by electron irradiation, revealing tunable exotic pairing states.

Findings

Carrier concentration and impurity scattering increase with irradiation.

Superconducting gap structure changes nonmonotonically with irradiation.

Superconductivity described by admixture of singlet and septet pairing.

Abstract

In superconductors, electrons with spin ${s=1/2}$ form Cooper pairs whose spin structure is usually singlet (${S=0}$) or triplet (${S=1}$). When the electronic structure near the Fermi level is characterized by fermions with angular momentum ${j=3/2}$ due to strong spin-orbit interactions, novel pairing states such as even-parity quintet (${J=2}$) and odd-parity septet (${J=3}$) states become allowed. Prime candidates for such exotic states are half-Heusler superconductors, which exhibit unconventional superconducting properties, but their pairing nature remains unsettled. Here we show that the superconductivity in the noncentrosymmetric half-Heusler LuPdBi can be consistently described by the admixture of isotropic even-parity singlet and anisotropic odd-parity septet pairing, whose ratio can be tuned by electron irradiation. From magnetotransport and penetration depth measurements, we find that carrier concentrations and impurity scattering both increase with irradiation, resulting in a nonmonotonic change of the superconducting gap structure. Our findings shed new light on our fundamental understanding of unconventional superconducting states in topological materials.