Fluctuation driven topological Hund insulators

TL;DR

This paper demonstrates that electron-electron interactions can induce a quantum spin Hall phase in a two-band Hubbard model, with phase transitions driven by local dynamical fluctuations and Mott physics.

Contribution

It reveals how interactions can turn a trivial insulator into a topological phase and maps the phase diagram using dynamical mean-field theory and Green's function topological invariants.

Findings

Interaction induces QSH phase in trivial systems

Strong interactions lead to Mott transition and trivial insulator

Phase diagram mapped via topological invariant calculations

Abstract

We investigate the role of electron-electron interaction in a two-band Hubbard model based on the Bernevig-Hughes-Zhang Hamiltonian exhibiting the quantum spin Hall (QSH) effect. By means of dynamical mean-field theory, we find that a system with topologically trivial non-interacting parameters can be driven into a QSH phase at finite interaction strength by virtue of local dynamical fluctuations. For very strong interaction, the system reenters a trivial insulating phase by going through a Mott transition. We obtain the phase diagram of our model by direct calculation of the bulk topological invariant of the interacting system in terms of its single particle Green's function.