THz phonon engineering and spectroscopy with van der Waals heterostructures

Phononic engineering at GHz frequencies forms the foundation of microwave acoustic filters, acousto-optic modulators, and quantum transducers. THz phononic engineering could lead to acoustic filters and modulators at higher bandwidth and speed, quantum circuits operating at higher temperatures, and new ways to manipulate thermal transport. Despite its potential, methods for engineering THz phonons have been little explored experimentally due to the challenges of achieving the required material control at sub-nm precision and efficient phonon coupling at THz frequencies. In this talk, we present efficient generation, detection, and manipulation of THz phonons through precise integration of atomically thin layers in van der Waals heterostructures. We employ few-layer graphene as an ultrabroadband transducer, converting fs near-infrared pulses to acoustic phonon pulses with spectral content up to 3 THz. A single layer of WSe₂ is used as a sensor, where high-fidelity readout is enabled by exciton-phonon coupling. By combining these capabilities, we performed THz phononic spectroscopy to obtain force constants of heterointerfaces and demonstrate high-Q THz phononic cavities. Furthermore, we show that a single layer of WSe₂ embedded in hBN can efficiently block the transmission of THz phonons. Our results could enable THz phononic metamaterials based on van der Waals heterostructures for ultrabroadband acoustic filters and modulators, as well as novel routes for thermal engineering.