Edge modes in the Hofstadter model of interacting electrons

TL;DR

This paper analyzes chiral edge modes in the Hofstadter model with interacting electrons, revealing topological phase transitions driven by Hubbard interactions and connecting edge behavior to Majorana fermion tunneling.

Contribution

It introduces a framework linking edge modes in the Hofstadter model to Majorana fermion tunneling, enabling analysis of topological transitions with interactions.

Findings

Edge modes are described by a Kitaev chain model.

Strong Hubbard interactions can collapse topological states.

A topological phase transition occurs at U=4Δ.

Abstract

We provide a detailed analysis of a realization of chiral gapless edge modes in the framework of the Hofstadter model of interacting electrons. In a transverse homogeneous magnetic field and a rational magnetic flux through an unit cell the fermion spectrum splits into topological subbands with well-defined Chern numbers, contains gapless edge modes in the gaps. It is shown that the behavior of gapless edge modes is described within the framework of the Kitaev chain where the tunneling of Majorana fermions is determined by effective hopping of Majorana fermions between chains. The proposed approach makes it possible to study the fermion spectrum in the case of an irrational flux, to calculate the Hall conductance of subbands that form a fine structure of the spectrum. In the case of a rational flux and a strong on-site Hubbard interaction $U$, $ U >4 \Delta $ ($ \Delta $ is a gap), the topological state of the system, which is determined by the corresponding Chern number and chiral gapless edge modes, collapses. When the magnitude of the on-site Hubbard interaction changes, at the point $ U = 4 \Delta $ a topological phase transition is realized, i.e., there are changes in the Chern numbers of two subbands due to their degeneration.