Floquet topological systems with flat bands: Edge modes, Berry curvature, and Orbital magnetization

TL;DR

This paper explores Floquet topological systems with flat bands, revealing edge modes, Berry curvature, and orbital magnetization, and compares static and driven models to uncover novel topological phases.

Contribution

It provides analytic expressions for edge modes and magnetization in Floquet flat bands, and demonstrates how Floquet driving induces new topological phases in the Haldane model.

Findings

Flat bands support chiral edge modes despite zero Chern number

Floquet driving induces Chern insulators and anomalous phases

Orbital magnetization is enhanced at half filling due to broken particle-hole symmetry

Abstract

Results are presented for Floquet systems in two spatial dimensions where the Floquet driving breaks an effective time reversal symmetry. The driving protocol also induces flat bands that correspond to anomalous Floquet phases where the Chern number is zero and yet chiral edge modes exist. Analytic expressions for the edge modes, Berry curvature, and the orbital magnetization are derived for the flat bands. Results are also presented for the static Haldane model for parameters when the bands are flat. Floquet driving of the same model is shown to give rise to Chern insulators as well as anomalous Floquet phases. The orbital magnetization for these different topological phases are presented and are found to be enhanced at half filling by the broken particle-hole symmetry of the Haldane model.