Time-Reversal Symmetry Breaking Superconductivity in Three-Dimensional Dirac Semimetallic Silicides

TL;DR

This study discovers that certain silicide superconductors break time-reversal symmetry and are three-dimensional Dirac semimetals, with evidence suggesting a nonunitary triplet superconducting state, which is promising for topological quantum computing.

Contribution

It provides the first experimental evidence of time-reversal symmetry breaking in (Ta, Nb)OsSi superconductors and links their topological semimetallic nature to unconventional superconductivity.

Findings

(Ta, Nb)OsSi are 3D Dirac semimetals protected by nonsymmorphic symmetries.

They exhibit spontaneous time-reversal symmetry breaking at superconducting transition.

The superconducting state is likely a nonunitary triplet pairing.

Abstract

Superconductors with broken time-reversal symmetry represent arguably one of the most promising venues for realizing highly sought-after topological superconductivity that is vital to fault-tolerant quantum computation. Here, by using extensive muon-spin relaxation and rotation measurements, we report that the isostructural silicide superconductors (Ta, Nb)OsSi spontaneously break time-reversal symmetry at the superconducting transition while surprisingly showing a fully-gapped superconductivity characteristic of conventional superconductors. The first-principles calculations show that (Ta, Nb)OsSi are three-dimensional Dirac semimetals protected by nonsymmorphic symmetries. Taking advantage of the exceptional low symmetry crystal structure of these materials, we have performed detailed theoretical calculations to establish that the superconducting ground state for both (Ta, Nb)OsSi is most likely a nonunitary triplet state.