Optical signatures of -1/3 fractional quantum anomalous Hall state in twisted MoTe2

TL;DR

This paper reports the optical detection of a fragile -1/3 fractional quantum anomalous Hall state in twisted MoTe2 bilayers, revealing its topological nature through photoluminescence and magnetic dichroism measurements supported by theoretical calculations.

Contribution

It provides the first optical evidence of the elusive -1/3 FQAH state in twisted MoTe2, confirming its topological character and tunability via electric field.

Findings

Detection of ferromagnetic states at specific filling factors

Observation of the -1/3 state's dispersion with magnetic field

Theoretical support for the topological nature of the state

Abstract

The discovery of fractional charge excitations in new platforms offers crucial insights into strongly correlated quantum phases. While a range of fractional quantum anomalous Hall (FQAH) states have recently been observed in two-dimensional twisted moire systems, the theoretically anticipated filling factor v = -1/3 FQAH state has remained elusive, with debates centering on its nature of charge density wave or a topological Chern insulator. Here, we report the optical detection of a v = -1/3 FQAH state in twisted MoTe2 bilayers. Using photoluminescence (PL) and reflective magnetic circular dichroism (RMCD) techniques, we identify ferromagnetic states at filling factors v = -1, -2/3, and -1/3, all tunable by a vertical electric field. The corresponding Curie temperatures are approximately 11 K, 3.5 K, and 2.4 K, respectively. The -1/3 state emerges over a narrower electric field range and a lower temperature compared to the integer and other fractional states, indicating its fragile nature that may lead to its absence in previous reports. Notably, the PL spectra at v = -1/3 disperse as the out-of-plane magnetic field increases, consistent with a nontrivial topological origin. Theoretical calculations based on the exact diagonalization method further support the interpretation of this topologically non-trivial state.