Interfacial phonon engineering in 2D heterostructures for cavity-less optomechanical systems

Two-dimensional materials such as graphene are expected to emerge as crucial platforms for on-chip integrated optomechanical systems due to their atomic-scale thickness, strong light–matter coupling, and tunable mechanical properties. However, conventional cavity optomechanical systems are constrained by low-temperature requirements and complex optical cavity configurations. Through interfacial engineering of van der Waals heterostructures and innovative design of phononic sensing layers, we have achieved an optical cavity-less excitonic optomechanical system operating at room temperature that combines high-frequency oscillatory characteristics with high quality factors. Picosecond ultrasonic pump–probe spectroscopy reveals photoinduced carrier-driven out-of-plane longitudinal coherent phonon dynamics in few and multilayer graphene, where electron–phonon coupling enhances optomechanical interactions. Systematic investigation of phonon dissipation mechanisms in supporting substrates (Si, sapphire, hBN, freestanding) identifies phonon radiative losses as the dominant factor, with substrate-free systems extending resonant phonon lifetimes from 58 to 201 ps. We propose utilizing exciton–phonon coupling in MoS2 sensing layers to effectively detect phonon pulses, ultimately achieving a characteristic f×Q product of 1.87×1013 Hz that surpasses the quantum sensing threshold (>6×1012 Hz) at room temperature. This work demonstrates that 2D heterostructures can replace physical cavities through exciton–phonon coupling to achieve phonon field localization, establishing an “exciton-resonance equivalent cavity” with enhanced acousto-optic coupling. These findings provide new strategies for quantum sensing, on-chip acoustic resonators, and non-destructive material characterization.