Hidden States and Dynamics in Moiré Quantum Matter

Moiré interfaces of two dimensional (2D) van der Waals (vdW) crystals constitute the most versatile platforms for the exploration of emergent quantum phases. Here, we take a time-domain view of moiré quantum matter. In this approach, a pump laser pulse excites charge across a manybody gap or disrupts correlation; a probe pulse tracks subsequent melting and recovery dynamics from exciton sensing. This is essentially a background-free spectroscopic technique when the pump light with photon energy below the quasi-particle gaps perturbs only the correlated states. The exquisite sensitivity and selectivity of this technique allow us to discover a large number of hidden quantum phases or understand the nature of known ones. In the first example, we explore the stability origins of correlated states in WSe₂/WS₂ moiré superlattices and discovered the polaronic nature of the one (v = -1) hole correlated insulator. The holon-doublon pair resulting from optical excitation is likely a polaronic Hubbard exciton. In contrast, the melting of the two (v = -2) hole correlated insulator is dominated plasmonic screening from free holons and doublons. 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. In second example, we apply the approach to the twisted MoTe₂ bilayer and show the discovery of a zoo of correlated states at fractional fillings that have escaped detection in transport and static optical sensing. More importantly, we discover at least six new states at fractional hole fillings of the 1^st and 2^nd Chern bands. These new fractional states are potential candidates for the coveted fractional topological insulators and/or non-abelian anyons.