A Zoo of Hidden States and Dynamics at Fractional Fillings of Topological Moiré Bands

Moiré interfaces of 2D van der Waals 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 many-body gap or disrupts correlation; a probe pulse tracks subsequent melting and recovery dynamics from exciton sensing. This is essentially a background-free technique when the pump photon energy is below quasi-particle gaps and perturbs only the correlated states. In the first example, we explore the stability origins of correlated states in WSe2/WS2 moiré superlattices and discovered the polaronic nature from strong electron-phonon coupling. We present evidence for the distinct nature of excitation across the correlation gaps for the n = -1 and -2 states: the former is likely a polaronic Hubbard exciton and the latter a free holon and doublon pair. In the second example, we apply the approach to the twisted MoTe2 bilayer (tMoTe2) for its richness of quantum phases, as exemplified by the landmark demonstrations of the fractional quantum anomalous Hall effect (FQAH). In addition to known states in tMoTe2, we discover 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 1st and 2nd Chern bands, n = -4/3, -3/2, -5/3, -7/3, -5/2, and -8/3. Some of these states are potential candidates for the coveted fractional topological insulators and/or non-abelian anyons. Moreover, we show the topological role in scattering and dynamics.