Interaction effects in a 1D flat band at a topological crystalline step edge

TL;DR

This study investigates how electron interactions affect one-dimensional edge channels at topological crystalline insulator step edges, revealing a correlation gap formation when the energy aligns with the Fermi level, combining experimental and theoretical insights.

Contribution

It provides the first combined experimental and theoretical analysis of interaction effects in 1D topological edge channels in a crystalline insulator.

Findings

Observation of a correlation gap near the Fermi level

Enhanced interaction effects due to 1D electronic density

Theoretical modeling with Hartree-Fock analysis

Abstract

Step edges of topological crystalline insulators can be viewed as predecessors of higher-order topology, as they embody one-dimensional edge channels embedded in an effective three-dimensional electronic vacuum emanating from the topological crystalline insulator. Using scanning tunneling microscopy and spectroscopy we investigate the behaviour of such edge channels in Pb$_{1-x}$Sn$_{x}$Se under doping. Once the energy position of the step edge is brought close to the Fermi level, we observe the opening of a correlation gap. The experimental results are rationalized in terms of interaction effects which are enhanced since the electronic density is collapsed to a one-dimensional channel. This constitutes a unique system to study how topology and many-body electronic effects intertwine, which we model theoretically through a Hartree-Fock analysis.