Edge Reconstruction of a Time-Reversal Invariant Insulator: Compressible-Incompressible Stripes

TL;DR

This paper investigates how smooth confining potentials induce alternating compressible and incompressible stripes at the edges of a 2D topologically trivial insulator, potentially leading to gapless edge modes and a novel metal-insulator transition.

Contribution

It reveals the emergence of gapless edge modes in trivial insulators due to edge reconstruction, a phenomenon previously associated mainly with topological phases.

Findings

Alternating compressible and incompressible stripes form at the edge.

Gapless edge modes can emerge in trivial insulators.

Incompressible stripes occur at specific fillings and may show charge density wave order.

Abstract

Two-dimensional (2D) topological electronic insulators are known to give rise to gapless edge modes, which underlie low energy dynamics, including electrical and thermal transport. This has been thoroughly investigated in the context of quantum Hall phases, and time-reversal invariant topological insulators. Here we study the edge of a 2D, topologically trivial insulating phase, as a function of the strength of the electronic interactions and the steepness of the confining potential. For sufficiently smooth confining potentials, alternating compressible and incompressible stripes appear at the edge. Our findings signal the emergence of gapless edge modes which may give rise to finite conductance at the edge. This would suggest a novel scenario of a nontopological metal-insulator transition in clean 2D systems. The incompressible stripes appear at commensurate fillings and may exhibit broken translational invariance along the edge in the form of charge density wave ordering. These are separated by structureless compressible stripes.