Mott transition and magnetism in a fragile topological insulator

TL;DR

This paper investigates how electronic correlations affect fragile topological insulators, revealing a transition to Mott insulators and magnetic phases, and demonstrating magnetic field-induced topological phase changes.

Contribution

It provides the first detailed analysis of the interplay between strong correlations, magnetism, and fragile topology using dynamical mean-field theory.

Findings

Fragile topology remains stable below a critical interaction strength.

A Mott transition occurs at high interaction strength, destroying fragile topology.

Magnetic fields can induce a transition from fragile to Chern insulator.

Abstract

We study the effects of electronic correlations on fragile topology using dynamical mean-field theory. Fragile topological insulators (FTIs) offer obstruction to the formation of exponentially localized Wannier functions, but they can be trivialized by adding certain trivial degrees of freedom. For the same reason, FTIs do not host symmetry-protected flow of edge states between bulk bands in cylindrical boundary conditions but are expected to have a spectral flow between the fragile bands and other bands under certain twisted boundary conditions. We here analyze commonly observed effects of strong correlations, such as the Mott-insulator transition and magnetism, on a known model hosting fragile topology. We show that in the nonmagnetic case, fragile topology, along with the twisted boundary states, is stable with interactions below a critical interaction strength. Above this interaction strength, a transition to the Mott insulating phase occurs, and the twisted boundary states disappear. Furthermore, by applying a homogeneous magnetic field, the fragile topology is destroyed. However, we show that a magnetic field can induce a topological phase transition which converts a fragile topological insulator to a Chern insulator. Finally, we study ferromagnetic solutions of the fragile topological model.