Aspects of Floquet Bands and Topological Phase Transitions in a Continuously Driven Superlattice

TL;DR

This paper investigates Floquet bands and topological phase transitions in a continuously driven Harper model, revealing nonzero Chern numbers, quantized transport, flat topological bands, Dirac cones, and edge modes, with implications for experimental realization.

Contribution

It provides a detailed analysis of topological properties and phase transitions in a continuously driven superlattice, highlighting features like nonzero Chern numbers and flat bands that are novel in this context.

Findings

Floquet bands generally have nonzero Chern numbers.

Topological phase transitions occur as system parameters are varied.

Flat, topologically nontrivial Floquet bands can emerge.

Abstract

Recently the creation of novel topological states of matter by a periodic driving field has attracted great attention. To motivate further experimental and theoretical studies, we investigate interesting aspects of Floquet bands and topological phase transitions in a continuously driven Harper model. In such a continuously driven system with an odd number of Floquet bands, the bands are found to have nonzero Chern numbers in general and topological phase transitions take place as we tune various system parameters, such as the amplitude or the period of the driving field. The nontrivial Floquet band topology results in a quantized transport of Wannier states in the lattice space. For certain parameter choices, very flat yet topologically nontrivial Floquet bands may also emerge, a feature that is potentially useful for the simulation of physics of strongly correlated systems. Some cases with an even number of Floquet bands may also have intriguing Dirac cones in the spectrum. Under open boundary conditions, anomalous counter-propagating chiral edge modes and degenerate zero modes are also found as the system parameters are tuned. These results should be of experimental interest because a continuously driven system is easier to realize than a periodically kicked system.