Time-Domain Signatures of Distinct Correlated Insulators in a Moir\'e Superlattice

TL;DR

This study uses pump-probe spectroscopy to identify distinct time-domain signatures of correlated insulators at different fillings in a moiré superlattice, revealing the roles of electron-phonon and electron-electron interactions.

Contribution

It introduces a non-equilibrium spectroscopy approach to differentiate correlated insulators based on their dynamic responses, highlighting the underlying interaction mechanisms.

Findings

Disordering time of v = -1 insulator is excitation density independent.

Disordering time of v = -2 insulator scales with (n_ex)^-0.5.

Distinct reordering behaviors suggest different quasiparticles involved.

Abstract

Among expanding discoveries of quantum phases in moir\'e superlattices, correlated insulators stand out as both the most stable and most commonly observed. Despite the central importance of these states in moir\'e 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 (v = -1) and two (v = -2) holes per moir\'e unit cell in the angle-aligned WSe2/WS2 system. Following photo-doping, we find that the disordering time of the v = -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 v = -2 state scales with (n_ex)^-0.5, in agreement with plasmonic screening from free holons and doublons. These states display disparate reordering behavior dominated either by first order (v = -1) or second order (v = -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 moir\'e landscape and establishes non-equilibrium responses as mechanistic signatures for distinguishing and discovering quantum phases.