Journal
NANO LETTERS
Volume 18, Issue 2, Pages 1082-1087Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.nanolett.7b04604
Keywords
van der Waals heterostructure; NanoARPES; electronic structure; electron-phonon coupling; polaron; Migdal-Eliashberg theory
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Funding
- Centre National de la Recherche Scientifique (CNRS), France
- Commissariat a l'Energie Atomique et aux Energies Alternatives (CEA), France
- National Basic Research Program of China (973 Program) [2013CB934500]
- National Natural Science Foundation of China (NSFC) [61325021]
- U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering [DE-AC02-76SF00515]
- U.S. Department of Energy, Office of Science [DE-AC02-05CH11231]
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van der Waals heterostructures, vertical stacks of layered materials, offer new opportunities for novel quantum phenomena which are absent in their constituent components. Here we report the emergence of polaron quasiparticles at the interface of graphene/hexagonal boron nitride (h-BN) heterostructures. Using nanospot angle-resolved photoemission spectroscopy, we observe zone-corner replicas of h-BN valence band maxima, with energy spacing coincident with the highest phonon energy of the heterostructure, an indication of Frohlich polaron formation due to forward-scattering electron-phonon coupling. Parabolic fitting of the h-BN bands yields an effective mass enhancement of similar to 2.3, suggesting an intermediate coupling strength. Our theoretical simulations based on Migdal-Eliashberg theory corroborate the experimental results, allowing the extraction of microscopic physical parameters. Moreover, renormalization of graphene pi-band is observed, due to the hybridization with the h-BN band. Our work generalizes the polaron study from transition metal oxides to van der Waals heterostructures with higher material flexibility, highlighting interlayer coupling as an extra degree of freedom to explore emergent phenomena.
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