Phononic frequency combs in twisted bilayer van der Waals material resonators

Abstract

This study investigates the generation of phononic frequency combs (PnFCs) in twisted bilayer MoS2 nanomechanical resonators through a combination of molecular dynamics (MD) simulations and continuum-discrete modeling. It is demonstrated that controlled twist angles between van der Waals layers induce symmetry-breaking effects that fundamentally alter the nonlinear vibrational characteristics. The resonator exhibits a (2:1) internal resonance condition due to mode splitting from anisotropic interlayer potential, as revealed by both MD and finite element analysis. The resonator shows strong nonlinear behavior under moderate driving amplitudes. It exhibits Duffing-type bifurcation with both softening and hardening branches, along with quasi-periodic vibrations visible as beat phenomena. Additionally, PnFCs emerge, whose comb teeth spacing can be tuned by varying the driving amplitude. A reduced two-degree-of-freedom model successfully captures the essential dynamics, including Neimark bifurcations observed in frequency sweeps. This work demonstrates that twisted van der Waals materials can serve as a promising platform for on-chip PnFCs generation, offering new degrees of freedom for controlling comb characteristics through twist-angle-engineered nonlinearities.