Signatures of moir\'e intralayer biexcitons and exciton-phason coupling in WSe2/WS2 heterostructures

Abstract

Interactions among electronic and lattice degrees-of-freedom are foundational to various phases in condensed-matter physics, yet the dynamic interplay between excitonic and phononic quasiparticles represents an equivalent, underexplored frontier. Moir\'e superlattices provide an ideal platform for realizing these interactions by offering localized intralayer excitons (IALX) and ultralow-energy collective lattice modes, such as phasons. Here, by optically suppressing ultrafast charge-transfer (CT) to interlayer excitons in WSe2/WS2 heterostructures, we uncover dynamics of moir\'e IALX revealing long lifetimes ({\tau} > 1000 ps) arising from localized Wannier and in-plane CT nature. We then observe moir\'e intralayer intervalley biexcitons with binding energy ~ 16 meV, with long lifetimes due to moir\'e confinement. Furthermore, we find time-domain signatures of strong coupling between moir\'e-IALX and ~ 10 micro-eV phasons, evidenced as twist-angle-dependent GHz oscillations in IALX dynamics. Our findings establish moir\'e superlattices as interacting hybrid quantum systems and for engineering non-equilibrium phenomena, as well as for GHz-scale optoelectronics.