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In sufficiently high magnetic fields, continuous electron bands are transformed into quantized Landau levels (LLs). Although the huge density and degeneracy of states inside the LLs seems at first glance to favor the interactions effects, the famous Kohn theorem [1] prohibits any many-body renormalization of the cyclotron frequency in the case of a parabolic band dispersion. Luckily for the Flat-Clubbers, most 2D materials show non-parabolic Dirac-like bands, to which the Kohn theorem does not apply. In particular, the optically induced LL transitions in graphene show strong many-body excitonic effects [2].

In this talk, I will discuss the current status of the LL excitons in graphene, with the focus on:

  • imaging of graphene magneto-excitons using magneto-SNOM [3];
  • breakdown of the canonical magneto-optical selection rules at finite momenta q [4];
  • hybridization of LL excitons with phonon-polaritons in graphene/hBN heterostructures [5];
  • B-field dependence of the LL-excitonic binding energy [5].

In the end, I’ll outline open questions and avenues in this field.

[1] W. Kohn, Cyclotron resonance and de Haas–van Alphen oscillations of an interacting electron gas. Phys. Rev. 123, 1242–1244 (1961).
[2] C. Faugeras et al, Landau Level Spectroscopy of Electron-Electron Interactions in Graphene, PRL 114, 126804 (2015)
[3] M. Dapolito et al, Infrared nano-imaging of Dirac magnetoexcitons in graphene, Nature Nanotechnology 18, 1409-1415 (2023)
[4] R. Roldán, J.-N. Fuchs, and M.O. Goerbig, Collective modes of doped graphene and a standard two-dimensional electron gas in a strong magnetic field: Linear magnetoplasmons versus magnetoexcitons. PRB 80, 085408 (2009).
[5] L. Wehmeier et al., Nano-Imaging of Landau-Phonon Polaritons in Dirac Heterostructures, arXiv:2312.14093.

If you want to join for pizza, please register at the doodle.

Location: Stuckelberg, Ecole de Physique
Time: Friday 8 March 2024, 12:10 for pizza, 12:30 start discussion