Interaction-Induced Topological and Magnetic Phases in the Hofstadter-Hubbard Model

TL;DR

This paper explores how many-body interactions induce topological and magnetic phases in the Hofstadter-Hubbard model using the effective topological Hamiltonian approach combined with DMFT, revealing phase diagrams with quantum spin Hall states and magnetic order.

Contribution

It introduces a method to determine topological invariants in interacting systems using the effective topological Hamiltonian with DMFT, applied to the Hofstadter-Hubbard model.

Findings

Interaction induces quantum spin Hall states at various interaction strengths.

Strong correlations and staggered potential lead to magnetic long-range order.

Phase diagram shows first order transition with magnetic and topological phases.

Abstract

Interaction effects have been a subject of contemporary interest in topological phases of matter. But in the presence of interactions, the accurate determination of topological invariants in their general form is difficult due to their dependence on multiple integrals containing Green's functions and their derivatives. Here we employ the recently proposed "effective topological Hamiltonian" approach to explore interaction-induced topological phases in the time-reversal-invariant Hofstadter-Hubbard model. Within this approach, the zero-frequency part of the self-energy is sufficient to determine the correct topological invariant. We combine the topological Hamiltonian approach with the local self-energy approximation, both for the static and the full dynamical self-energy evaluated using dynamical mean field theory (DMFT), and present the resulting phase diagram in the presence of many-body interactions. We investigate the emergence of quantum spin Hall (QSH) states for different interaction strengths by calculating the $\mathbb{Z}_2$ invariant. The interplay of strong correlations and a staggered potential also induces magnetic long-range order with an associated first order transition. We present results for the staggered magnetization ( $m_s$ ), staggered occupancy ( $n_s$ ), and double occupancy across the transition.