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

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 ν=-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 ν=-1/3 FQAH state in twisted MoTe_{2} bilayers. Using photoluminescence and reflective magnetic circular dichroism techniques, we identify ferromagnetic states at filling factors ν=-1, -2/3, and -1/3, all tunable by a vertical electric field. The corresponding Curie temperatures are approximately 11, 3.5, 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 a fragile nature that may have led to its absence in previous reports. Notably, the photoluminescence spectra at ν=-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 nontrivial state.