Kavli Affiliate: Feng Wang
| First 5 Authors: Yoseob Yoon, Zheyu Lu, Can Uzundal, Ruishi Qi, Wenyu Zhao
| Summary:
Phononic engineering at gigahertz (GHz) frequencies form the foundation of
microwave acoustic filters, acousto-optic modulators, and quantum transducers.
Terahertz (THz) phononic engineering could lead to acoustic filters and
modulators at higher bandwidth and speed, as well as quantum circuits operating
at higher temperatures. Despite its potential, methods for engineering THz
phonons have been limited due to the challenges of achieving the required
material control at sub-nanometer precision and efficient phonon coupling at
THz frequencies. Here, we demonstrate 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 (FLG) as
an ultrabroadband phonon transducer, converting femtosecond near-infrared
pulses to acoustic phonon pulses with spectral content up to 3 THz. A monolayer
WSe$_2$ is used as a sensor, where high-fidelity readout is enabled by the
exciton-phonon coupling and strong light-matter interactions. Combining these
capabilities in a single heterostructure and detecting responses to incident
mechanical waves, we perform THz phononic spectroscopy. Using this platform, we
demonstrate high-Q THz phononic cavities and show that a monolayer WSe$_2$
embedded in hexagonal boron nitride (hBN) can efficiently block the
transmission of THz phonons. By comparing our measurements to a nanomechanical
model, we obtain the force constants at the heterointerfaces. Our results could
enable THz phononic metamaterials for ultrabroadband acoustic filters and
modulators, and open novel routes for thermal engineering.
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