Valley-Selective Topological Ordered States in Irradiated Bilayer Graphene

TL;DR

This paper demonstrates how applying electric fields and circularly polarized light to bilayer graphene can selectively induce topological ordered states with distinct valley properties, leading to coexistence of quantized Hall effects.

Contribution

It introduces a method to control valley-specific topological states in bilayer graphene using Floquet engineering, revealing new states with coexisting quantized Hall conductivities.

Findings

Selective valley polarization achieved with external fields.

Multiple topological states stabilized and distinguished by edge transport.

Coexistence of quantized charge, spin, and valley Hall effects.

Abstract

Gapless bilayer graphene is susceptible to a variety of spontaneously gapped states. As predicted by theory and observed by experiment, the ground state is however topologically trivial, because a valley-independent gap is energetically favorable. Here, we show that under the application of interlayer electric field and circularly polarized light, one valley can be selected to exhibit the original interaction instability while the other is frozen out. Tuning this Floquet system stabilizes multiple competing topological ordered states, distinguishable by edge transport and circular dichroism. Notably, quantized charge, spin, and valley Hall conductivities coexist in one stabilized state.