Symmetry-protected topological invariant and Majorana impurity states in time-reversal-invariant superconductors

TL;DR

This paper investigates how nonmagnetic impurities can induce zero-energy states in time-reversal-invariant topological superconductors, introducing a symmetry-based topological invariant and demonstrating impurity-driven topological phase transitions.

Contribution

It defines a new symmetry-based topological invariant in real space and applies it to show impurity-induced topological phase changes in a specific superconductor model.

Findings

Impurities can induce zero-energy states protected by symmetry.

A position-space Z_2 invariant relates to bulk topological properties.

Impurity lattices can transform trivial phases into nontrivial topological phases.

Abstract

We address the question of whether individual nonmagnetic impurities can induce zero-energy states in time-reversal-invariant topological superconductors, and define a class of symmetries which guarantee the existence of such states for a specific value of the impurity strength. These symmetries allow the definition of a position-space topological Z_2 invariant, which is related to the standard bulk topological Z_2 invariant. Our general results are applied to the time-reversal-invariant p-wave phase of the doped Kitaev-Heisenberg model, where we demonstrate how a lattice of impurities can drive a topologically trivial system into the nontrivial phase.