Floquet Engineering

By harnessing synthesized optical lightwaves, we can engineer topological and quantum properties in materials through optical dressing, creating novel out-of-equilibrium states. Recent examples are Floquet engineering in 2D semiconductors, where we demonstrated Floquet replicas of excitonic states or the generation of a Floquet topological insulator (FTI) in graphene.  These states exhibit unique optical and electrical properties. In FTIs, these states arise from the interplay between light-induced symmetry breaking and the intrinsic topology of the material, governed by quantities like the Berry curvature and Chern numbers. The Chern number, an integer-valued topological invariant, quantifies the global properties of electronic bands and determines the presence of conducting edge states in Floquet systems. By tuning the lightwave parameters—such as intensity, polarization, and frequency—we aim to dynamically control these invariants, potentially enabling ultrafast switching between topological phases. Lightwave-controlled band engineering promises ultrafast information storage and readout and opens up avenues for subfemtosecond-controllable band structures.

We will experimentally create these states and investigate their properties using advanced spectroscopy techniques, including transient absorption, all-optical anomalous Hall effect measurements, photocurrent circular dichroism, and valley-selective current detection. These developments form the foundation for lightwave-driven Floquet electronics.