Emergence of Frohlich polaron from interlayer electron-phonon coupling in van der Waals heterostructure

摘要

Van der Waals heterostructures, vertical stacks of layered materials, offernewopportunities for novel quantum phenomena which are absent in theirconstituent components. Here we report the emergence of polaron quasiparticlesat the interface of graphene/hexagonal boron nitride (h-BN) heterostructures.Using nanospot angle-resolved photoemission spectroscopy, we observezone-corner replicas of h-BN valence band maxima, with energy spacingcoincident with the highest phonon energy of the heterostructure|an indicationof Frohlich polaron formation due to forward scattering electron-phononcoupling. Parabolic fitting of the h-BN bands yields an effective massenhancement of ~ 2.3, suggesting an intermediate coupling strength. Ourtheoretical simulations based on Migdal-Eliashberg theory corroborate theexperimental results, allowing the extraction of microscopic physicalparameters. Moreover,renormalisation of graphene $\pi$ band is observed due tothe hybridisation with the h-BN band. Our work generalises the polaron studyfrom transition metal oxides to Van derWaals heterostructures with highermaterial exibility, highlighting interlayer coupling as an extra degree offreedom to explore emergent phenomena.