Topological superconductor in quasi-one-dimensional Tl2-xMo6Se6

TL;DR

This paper predicts that Tl2-xMo6Se6 is a topological superconductor with unique triplet pairing and nematic order, even without spin-orbit coupling, expanding understanding of unconventional superconductivity in low-dimensional materials.

Contribution

It introduces Tl2-xMo6Se6 as a potential topological superconductor with novel pairing symmetry and nematic order, independent of spin-orbit coupling effects.

Findings

Superconductivity persists in Tl-deficient compounds.

Triplet d vector prefers orientation perpendicular to chains.

Nematic order arises from spontaneous symmetry breaking.

Abstract

We propose that the quasi-one-dimensional molybdenum selenide compound Tl2-xMo6Se6 is a time-reversal-invariant topological superconductor induced by inter-sublattice pairing, even in the absence of spin-orbit coupling (SOC). No noticeable change in superconductivity is observed in Tl-deficient (0<=x<=0.1) compounds. At weak SOC, the superconductor prefers the triplet d vector lying perpendicular to the chain direction and two-dimensional E2u symmetry, which is driven to a nematic order by spontaneous rotation symmetry breaking. The locking energy of the d vector is estimated to be weak and hence the proof of its direction would rely on tunnelling or phase-sensitive measurements.