Long-lived nonequilibrium phonons in twisted Van der Waals heterostructures

Abstract

Ultrafast electron diffraction (UED) measurements on twisted WSe2/MoSe2 heterobilayers reveal that zone-edge M-point phonons retain polarized, non-thermal populations with decay constants nearly twice the monolayer value. To uncover the microscopic scattering pathways governing these lifetimes, we developed a first-principles framework coupling the time-dependent Boltzmann equation (TDBE) with split machine-learned interatomic potentials and a multiphonon diffuse scattering formalism. Our simulations quantitatively reproduce the measured distributions, identify K-to-Q intervalley electron-phonon scattering as the dominant source of zone-edge phonon populations, and reveal that moiré superlattices selectively suppress momentum-redistributing decay channels for M-point modes. These results demonstrate the viability of twisted TMDC heterostructures as a tunable platform for decoupling phonon momentum thermalization from energy relaxation.