Floquet engineering of band structure topology

Floquet engineering is the idea to manipulate the electronic properties of solids with periodic, tailored light. Especially light-induced "on-demand" topology is in the spotlight of many theoretical studies. However, experiments are scarce due to fundamental challenges; especially laser-heating, electron-electron and electron-phonon scattering play a crucial role, and are usually unaccounted for by most theory predictions. Therefore, bridging the gap between the many theoretical proposals and experimental realization requires a new paradigm. The key ideas investigated in our group are:

• Identifying realistic of regimes of Floquet engineering. There are many hints that electron­-electron an electron­-phonon scattering are adversarial to the Floquet state, and need to be taken into account. This calls for new paradigms centering on coherence and avoiding laser­ heating, which requires a predictive nonequilibrium theory. We apply the state-of-the-art time­-dependent Green’s function methods and work out the underlying principles and suggest the best candidate materials and regimes for observing Floquet physics in time-resolved photoemission.

• Nonequilibrium Berry curvature spectroscopy. Employing the power of (simulating) multi-dimensional ARPES, we are searching for hallmarks of light-induced topological states beyond hard-to-measure features like gap openings or non-quantized Hall responses.

Relevant publications:

1. Theory of subcycle time-resolved photoemission: application to terahertz photodressing in graphene
   M. Schüler, M. A. Sentef
   J. Elec. Spect. Rel. Phen. 253, 147121 (2021) [special issue on trARPES]

2. How Circular Dichroism in Time- and Angle-Resolved Photoemission Can Be Used to Spectroscopically Detect Transient Topological States in Graphene
   M. Schüler, U. De Giovannini, H. Hübener, A. Rubio, M. A. Sentef, T. P. Devereaux, P. Werner
   Phys. Rev. X 10, 041013 (2020)