Higher-order topological insulators in a magnetic field

TL;DR

This paper explores higher-order topological insulators in a 2D SSH model under a magnetic field, revealing a wide gap at π flux that hosts HOTI phases, characterized by entanglement polarization, with potential HOTI existence even in weak fields.

Contribution

It demonstrates the presence of HOTI phases in a 2D SSH model under magnetic flux, especially around π flux, using entanglement polarization for characterization.

Findings

A wide gap around π flux hosts HOTI phases.

HOTI can exist in small gaps even under weak magnetic fields.

Entanglement polarization effectively characterizes HOTI under magnetic fields.

Abstract

Two-dimensional (2D) generalization of the Su-Schriffer-Heeger (SSH) model serves as a platform for exploring higher-order topological insulators (HOTI). We investigate this model in a magnetic field which interpolates two models studied so far with zero flux and $\pi$ flux per plaquette. We show that in the Hofstadter butterfly there appears a wide gap around the $\pi$ flux, which belongs to the same HOTI discovered by Benalcazar-Bernevig-Hughes (BBH). It turns out that in a weak field regime HOTI could exist even within a small gap disconnected from the wider gap around $\pi$ flux. To characterize HOTI, we employ the entanglement polarization (eP) technique which is useful even if the basic four bands split into many Landau levels under a magnetic field.