Terahertz phonon engineering with van der Waals heterostructures

TL;DR

This paper demonstrates the generation, detection, and manipulation of terahertz phonons in van der Waals heterostructures, enabling advanced phononic devices and quantum applications at higher frequencies and temperatures.

Contribution

It introduces a novel platform integrating atomically thin layers for efficient THz phonon control, including high-Q cavities and phonon blocking, advancing phononic engineering at terahertz frequencies.

Findings

Successful generation of up to 3 THz phonons using few-layer graphene.

High-fidelity readout of phonons via exciton-phonon coupling in WSe₂.

Demonstration of THz phononic cavities and phonon blocking in heterostructures.

Abstract

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.