Hidden States and Dynamics of Fractional Fillings in tMoTe2 Moir\'e Superlattices

TL;DR

This study uses transient optical spectroscopy to uncover nearly 20 hidden fractional quantum states in twisted MoTe2 bilayers, revealing new potential topological phases and distinct melting dynamics of correlated states.

Contribution

It introduces a novel optical spectroscopy approach to detect hidden fractional states in tMoTe2, expanding understanding of its complex quantum phases beyond static measurements.

Findings

Discovered nearly 20 hidden fractional states absent in static measurements.

Observed new states at fractional fillings like -4/3, -3/2, -5/3, etc.

Identified two distinct melting time scales for correlated states, 2-4 ps and 180-270 ps.

Abstract

The fractional quantum anomalous Hall (FQAH) effect was recently discovered in twisted MoTe2 bilayers (tMoTe2). Experiments to date have revealed Chern insulators from hole doping at v = -1, -2/3, -3/5, and -4/7 (per moir\'e unit cell). In parallel, theories predict that, between v = -1 and -3, there exist exotic quantum phases, 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 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. A probe pulse detects the subsequent melting and recovery dynamics via exciton and trion sensing. Besides the known states, we observe additional fractional fillings between v = 0 and -1 and a large number of states on the electron doping side (v > 0). Most importantly, we observe new states at fractional fillings of the Chern bands at v = -4/3, -3/2, -5/3, -7/3, -5/2, and -8/3. These states are potential candidates for the predicted exotic topological phases. 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 moir\'e conduction and valence bands.