Strong correlations at topological insulator surfaces and the breakdown of the bulk-boundary correspondence

TL;DR

This paper explores how strong electron correlations can be induced on topological insulator surfaces, leading to gapped states despite the bulk's topological predictions, by tuning Coulomb interactions experimentally.

Contribution

It introduces a mechanism to enhance Coulomb interactions on topological insulator surfaces, challenging the conventional bulk-boundary correspondence.

Findings

Strong correlations can gap surface states

Coulomb interaction strength can be experimentally tuned

Surface states may become gapped despite topological predictions

Abstract

The criteria for strong correlations on surfaces of three-dimensional topological insulators are discussed. Usually, the Coulomb repulsion at such surfaces is too weak for driving a phase transition to a strongly correlated regime. I discuss a mechanism and possibilities of its experimental implementation by which the strength of the Coulomb interaction can be tuned over a wide range. In the strongly interacting regime, the surface states are gapped, even though the topological classification of the bulk band structure predicts gapless surface states.