Landau-Phonon Polaritons in Graphene/hBN Heterostructures: A Nanoscopy Perspective

Mengkyn Liu
Stony Brook University – Stony Brook, New York, USA
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Hexagonal boron nitride (hBN) serves as a versatile platform for hosting polaritonic phenomena in low-dimensional materials. We report on a novel type of polaritons—Landauphonon polaritons (LPPs)—emerging from the hybridization of Dirac magnetoexciton modes in graphene with waveguide phonon polariton modes of hBN. Using infrared magneto-nanoscopy, we directly imaged LPP propagation and achieved real-space control by tuning the magnetic field. These polaritons exhibit large in-plane momenta, overcoming conventional optical selection rules to reveal “forbidden” inter-Landau level transitions (ILTs). Strong coupling between magnetoexciton and hBN phonon modes was evidenced by avoided crossings in LPP dispersion when their frequencies matched. Furthermore, our study unveiled fundamental manybody effects, including graphene Fermi velocity renormalization and ILT-dependent magnetoexciton binding energies.

Email: mengkun.liu@stonybrook.edu