Quantum geometric non-linear opto-electronic effects in topological flat bands and metals with realistic relaxations

• Applicant: Professor Dr. Inti Sodemann Villadiego
• Subject Area: Theoretical Condensed Matter Physics
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 555335098

When electrons move in crystals without an inversion center they can display a net directed rectified collective flow in response to purely oscillatory electric fields (namely a type of ratchet effect). Such "bulk-photovoltaic" effects can have rich interplays with the band structure dispersion of the Bloch states and their quantum geometry, and can also be relevant in the search for novel opto-electronic technologies. However, often the most popular theories to calculate such effects in materials do not account microscopically for relaxation and scattering processes, such as electron-phonon and electron-impurity scattering, as well as radiative photon emission processes. Accounting for these effects can lead to dramatically different predictions for example for the shift-current effect, in particular for systems without a gap and also in systems with very flat bands. The advent of a rich variety of flat-band systems with a rich quantum geometry and topology, such as the moiré systems, therefore calls for the development of theories of bulk-photo-current effects that systematically account for such relaxation mechanisms. These are precisely the key goals of this proposal: to develop theories of bulk photo-voltaic effects in systems without gaps and at low frequencies (metals and semi-metals) and also in flat band systems, with particular emphasis on twisted moiré dichalcogenides, while taking into account the realistic scattering and relaxation effects present in these systems.

• DFG Programme: Research Grants