A Time-Reversal Invariant Topological Phase at the Surface of a 3D Topological Insulator

TL;DR

This paper constructs a novel 3D topological insulator surface phase that preserves time-reversal and charge conservation symmetries, hosting non-Abelian anyons and Majorana zero modes, expanding understanding of topological surface states.

Contribution

It introduces a minimal gapped topological phase at the surface of a 3D topological insulator that maintains both symmetries and supports non-Abelian anyons, derived from vortex condensation.

Findings

Supports Ising-type non-Abelian anyons

Supports Majorana zero modes on vortices

Distinct from known topological phases

Abstract

A 3D fermionic topological insulator has a gapless Dirac surface state protected by time-reversal symmetry and charge conservation symmetry. The surface state can be gapped by introducing ferromagnetism to break time-reversal symmetry, introducing superconductivity to break charge conservation, or entering a topological phase. In this paper, we construct a minimal gapped topological phase that preserves both time-reversal and charge conservation symmetries and supports Ising-type non-Abelian anyons. This phase can be understood heuristically as emerging from a surface s-wave superconducting state via the condensation of eight-vortex composites. The topological phase inherits vortices supporting Majorana zero modes from the surface superconducting state. However, since it is time-reversal invariant, the surface topological phase is a distinct phase from the Ising topological phase, which can be viewed as a quantum-disordered spin-polarized p_x + i p_y superconductor. We discuss the anyon model of this topological phase and the manner in which time-reversal symmetry is realized in it. We also study the interfaces between the topological state and other surface gapped phases.