Anomalous edge states and topological phases of a kicked quantum Hall system

Periodically driven quantum Hall system at a fixed flux is found to exhibit a series of phases featuring anomalous edge modes with the “wrong” chirality. This leads to pairs of counter-propagating chiral edge modes at each edge, in sharp contrast to stationary quantum Hall systems. We show that these anomalous edge modes are robust against weak disorder. They are essential in distinguishing phases with the same Chern and winding numbers. Their existence thus challenges the existing framework describing the topological properties of driven systems. We explore their origin using a simplified model and discuss their experimental signatures.