Hidden states and dynamics of fractional fillings in twisted MoTe2 bilayers (2025)

Abstract

The fractional quantum anomalous Hall (FQAH) effect was recently discovered in twisted MoTe₂ bilayers (tMoTe₂)^1–4. Experiments to date have revealed Chern insulators from hole doping at ν = -1, -2/3, -3/5, and -4/7 (per moiré unit cell) ^1–6. In parallel, theories predict that, between v = -1 and -3, there exist exotic quantum phases ^7–15, such as the coveted fractional topological insulators (FTI), fractional quantum spin Hall (FQSH) states, and non-abelian fractional states. Here we employ transient optical spectroscopy ^16,17 on tMoTe₂ to reveal nearly 20 hidden states at fractional fillings that are absent in static optical sensing or transport measurements. A pump pulse selectively excites charge across the correlated or pseudo gaps, leading to the disordering (melting) of correlated states ¹⁸. A probe pulse detects the subsequent melting and recovery dynamics via exciton and trion sensing ^1,3,19–21. Besides the known states, we observe additional fractional fillings between ν = 0 and -1 and a large number of states on the electron doping side (ν > 0). Most importantly, we observe new states at fractional fillings of the Chern bands at ν = -4/3, -3/2, -5/3, -7/3, -5/2, and -8/3. These states are potential candidates for the predicted exotic topological phases ^7–15. Moreover, we show that melting of correlated states occurs on two distinct time scales, 2-4 ps and 180-270 ps, attributed to electronic and phonon mechanisms, respectively. We discuss the differing dynamics of the electron and hole doped states from the distinct moiré conduction and valence bands.