Exciton condensation and charge fractionalization in a topological insulator film

TL;DR

This paper demonstrates that in a topological insulator thin film under bias, electron-hole pairs can form a topological exciton condensate with unique properties, including fractional charge vortices, revealing novel quantum phenomena.

Contribution

It introduces the concept of a topological exciton condensate in topological insulator films and explores its unique fractionalized excitations, expanding understanding of topological quantum states.

Findings

Existence of a topological exciton condensate in biased topological insulator films.

Presence of fractional charge ±e/2 associated with vortices in the condensate.

Distinct topological properties compared to exciton condensates in graphene bilayers.

Abstract

An odd number of gapless Dirac fermions is guaranteed to exist at a surface of a strong topological insulator. We show that in a thin-film geometry and under external bias, electron-hole pairs that reside in these surface states can condense to form a coherent exciton condensate, similar in general terms to the exciton condensate recently argued to exist in a biased graphene bilayer, but with different topological properties. Such a `topological' exciton condensate (TEC) exhibits a host of unusual properties; the most interesting among them is the fractional charge +-e/2 carried by a singly quantized vortex in the TEC order parameter.