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  Light-matter coupling and quantum geometry in moiré materials

Topp, G. E., Eckhardt, C., Kennes, D. M., Sentef, M. A., & Törmä, P. (2021). Light-matter coupling and quantum geometry in moiré materials. Physical Review B, 104(6): 064306. doi:10.1103/PhysRevB.104.064306.

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PhysRevB.104.064306.pdf (Publisher version), 2MB
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2021
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© American Physical Society

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https://arxiv.org/abs/2103.04967 (Preprint)
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https://dx.doi.org/10.1103/PhysRevB.104.064306 (Publisher version)
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 Creators:
Topp, G. E.1, Author
Eckhardt, C.2, 3, 4, 5, Author              
Kennes, D. M.2, 4, 6, Author
Sentef, M. A.3, 4, Author
Törmä, P.1, Author
Affiliations:
1Department of Applied Physics, Aalto University, ou_persistent22              
2Institute for Theory of Statistical Physics, RWTH Aachen University, and JARA Fundamentals of Future Information Technology, ou_persistent22              
3Theoretical Description of Pump-Probe Spectroscopies in Solids, Theory Department, Max Planck Institute for the Structure and Dynamics of Matter, Max Planck Society, ou_3012828              
4Center for Free Electron Laser Science, ou_persistent22              
5International Max Planck Research School for Ultrafast Imaging & Structural Dynamics (IMPRS-UFAST), Max Planck Institute for the Structure and Dynamics of Matter, Max Planck Society, ou_2266714              
6Theory Group, Theory Department, Max Planck Institute for the Structure and Dynamics of Matter, Max Planck Society, ou_2266715              

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 Abstract: Quantum geometry has been identified as an important ingredient for the physics of quantum materials and especially of flat-band systems, such as moiré materials. On the other hand, the coupling between light and matter is of key importance across disciplines and especially for Floquet and cavity engineering of solids. Here we present fundamental relations between light-matter coupling and quantum geometry of Bloch wave functions, with a particular focus on flat-band and moiré materials, in which the quenching of the electronic kinetic energy could allow one to reach the limit of strong light-matter coupling more easily than in highly dispersive systems. We show that, despite the fact that flat bands have vanishing band velocities and curvatures, light couples to them via geometric contributions. Specifically, the intraband quantum metric allows diamagnetic coupling inside a flat band; the interband Berry connection governs dipole matrix elements between flat and dispersive bands. We illustrate these effects in two representative model systems: (i) a sawtooth quantum chain with a single flat band and (ii) a tight-binding model for twisted bilayer graphene. For (i) we highlight the importance of quantum geometry by demonstrating a nonvanishing diamagnetic light-matter coupling inside the flat band. For (ii) we explore the twist-angle dependence of various light-matter coupling matrix elements. Furthermore, at the magic angle corresponding to almost flat bands, we show a Floquet-topological gap opening under irradiation with circularly polarized light despite the nearly vanishing Fermi velocity. We discuss how these findings provide fundamental design principles and tools for light-matter-coupling-based control of emergent electronic properties in flat-band and moiré materials.

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Language(s): eng - English
 Dates: 2021-07-162021-03-092021-08-032021-08-162021-08-01
 Publication Status: Published in print
 Pages: -
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 Table of Contents: -
 Rev. Type: Peer
 Identifiers: arXiv: 2103.04967
DOI: 10.1103/PhysRevB.104.064306
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Title: Physical Review B
  Abbreviation : Phys. Rev. B
Source Genre: Journal
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Publ. Info: Woodbury, NY : American Physical Society
Pages: - Volume / Issue: 104 (6) Sequence Number: 064306 Start / End Page: - Identifier: ISSN: 1098-0121
CoNE: https://pure.mpg.de/cone/journals/resource/954925225008