Interlayer Phonon Coupling and Enhanced Electron-Phonon Interactions in Doubly Aligned hBN/Graphene/hBN Heterostructures.

Engineering the band structure via moiré superlattices plays a crucial role in tailoring the electronic and phononic spectra of hBN/graphene heterostructures, enabling a range of emergent properties. While moiré heterostructures have been extensively studied through transport measurements to investigate electronic spectra, their influence on the phononic spectrum, particularly on phonon-phonon and electron-phonon interactions, remains less explored. In this study, we examine the temperature-dependent (8 K-300 K) frequency and line width responses of the phonon near the K-point of graphene in hBN/graphene/hBN heterostructures for nonaligned, partially aligned, singly aligned, and doubly aligned configurations. The nonaligned samples, where the graphene is rotated by 30° with respect to both top and bottom hBN, exhibit pristine graphene behavior, characterized by minimal frequency variation with temperature and a typical line width increase with increasing temperature. In contrast, doubly aligned samples, where graphene and both hBN are perfectly aligned, display anomalous behavior, with the Raman frequency decreasing linearly and the lifetime increasing with increasing temperature. This anomalous anharmonic response could not be explained by the existing models considering only intralayer (within the graphene) phonon-phonon interactions, but rather indicates the role of strong interlayer phonon-phonon coupling (between hBN and graphene phonons), hitherto not observed. Furthermore, the enhanced electron-phonon interactions due to the resonant condition of phonon decay into electronic channels of doubly aligned hBN/graphene/hBN heterostructures explain the observed line width behavior. Our findings demonstrate the ability to engineer phonon-phonon and electron-phonon interactions through the precise alignment of hBN and graphene lattices, with implications for thermal management and carrier transport optimization in hBN/graphene/hBN heterostructures.