Engineering Interlayer Electron-Phonon Coupling in WS₂/h-BN Heterostructures

The nonadiabatic electron-phonon coupling (EPC) is ubiquitous in condensed matter physics and materials science, and plays a critical role in areas of transport scattering, conventional superconductivity, optical properties, spintronics, and quantum information. Particularly in van der Waals (vdW) heterostructures, the non-local interlayer EPC, which bridges electrons and phonons belonging to different layers, provides one unique channel to engineer these elementary particles, realizing emergent quantum behaviors. However, in-depth exploration of interlayer EPC effects is limited by stringent conditions for occurrence, and the efficient engineering of the interlayer EPC strength has remained elusive. Here we report a multi-tier engineering approach of studying the interlayer EPC in WS₂/hexagonal boron nitride (h-BN) heterostructures, including the isotope enrichment of h-BN substrates (h-¹⁰BN and h-¹¹BN), temperature tuning, and application of high pressures. The hyperfine, robust isotope dependence of Raman intensities was unambiguously revealed in isotopically-engineered heterostructures. Combined with theoretical calculations, we anticipate that the WS₂/h-BN supercell could induce Brillouin-zone-folded phonons which contribute to the interlayer coupling, leading to complex nature of the broad Raman peaks at ~800 cm^-1. We further demonstrate the significance of a previously unexplored parameter, the interlayer spacing between WS₂ and h-BN. By varying temperature and applying high pressure, we can effectively manipulate the strength of the interlayer coupling with turn-on/off capabilities, indicating the critical thresholds of the layer-layer spacing for activating and strengthening the interlayer EPC. Our findings provide new opportunities to engineer van der Waals heterostructures with controlled interlayer coupling.