Time-domain signatures of distinct correlated insulators in a moiré superlattice

Abstract

Among expanding discoveries of quantum phases in moiré superlattices, correlated insulators stand out as both the most stable and most commonly observed. Despite the central importance of these states in moiré physics, little is known about their underlying nature. Here, we use pump-probe spectroscopy to show distinct time-domain signatures of correlated insulators at fillings of one (ν = -1) and two (ν = -2) holes per moiré unit cell in the angle-aligned WSe₂/WS₂ system. Following photo-doping, we find that the disordering time of the ν = -1 state is independent of excitation density (n_ex), as expected from the characteristic phonon response time associated with a polaronic state. In contrast, the disordering time of the ν = -2 state scales with $1/\sqrt{n_{\text{ex}}}$ , in agreement with plasmonic screening from free holons and doublons. These states display disparate reordering behavior dominated either by first order (ν = -1) or second order (ν = -2) recombination, suggesting the presence of Hubbard excitons and free carrier-like holons/doublons, respectively. Our work delineates the roles of electron-phonon (e-ph) versus electron-electron (e-e) interactions in correlated insulators on the moiré landscape and establishes non-equilibrium responses as mechanistic signatures for distinguishing and discovering quantum phases.