Unconventional quantum Hall effect in Floquet topological insulators

TL;DR

This paper explores an unconventional quantum Hall effect in Floquet topological insulators, revealing a novel Hall state with half-integer quantization of Hall conductivity induced by photon dressing and polarization reversal.

Contribution

It demonstrates a new quantum Hall state in Floquet topological insulators where the zeroth Landau level transitions to a Hall insulator with half-integer quantization, influenced by light polarization.

Findings

Discovery of a Hall insulator state with σ_{yx}=e^2/2h

Reversal of light polarization exchanges surface states

Potential for observing half-integer quantum Hall plateaux

Abstract

We study an unconventional quantum Hall effect for the surface states of ultrathin Floquet topological insulators in a perpendicular magnetic field. The resulting band structure is modified by photon dressing and the topological property is governed by the low-energy dynamics of a single surface. An exchange of symmetric and antisymmetric surface states occurs by reversing the light's polarization. We find a novel quantum Hall state in which the zeroth Landau level undergoes a phase transition from a trivial insulator state, with Hall conductivity $\sigma_{yx}=0$ at zero Fermi energy, to a Hall insulator state with $\sigma_{yx}=e^2/2h$. These findings open new possibilities for experimentally realizing nontrivial quantum states and unusual quantum Hall plateaux at $(\pm1/2,\pm3/2,\pm5/2,...)e^2/h$.