The interplay among electronic correlation, topology, and time-reversal-symmetry (TRS) often leads to exotic quantum states of matter, as highlighted by the discoveries of fractional Chern insulators (FCIs) in twisted bilayer MoTe₂ [1-4] and rhombohedral graphene multilayers [5]. Among the FCIs in twisted bilayer MoTe₂, the most robust is at a hole filling factor of 𝜈 = −2/3
per moiré unit cell. Here, employing pump-probe modulation spectroscopy on twisted bilayer MoTe₂ [6], we show that a correlated state at 𝜈 = −4/3 exhibits an unusual Ising antiferromagnet behavior [7]. The 𝜈 = −4/3 state with no net magnetization undergoes first order phase transitions at extremely low magnetic fields of |µ0H| ~ 2-6 mT to partially valley polarized (PVP) states. The observed magnetic signature is consistent with a theoretically proposed fractional topological insulator (FTI), consisting of two copies of 𝜈± = −2/3 FCIs with opposite chirality in the 𝐾± valleys. The experimental results are supported by interacting continuum model calculations. Our findings present a candidate FTI with TRS and call for advanced transport and imaging measurements to establish the quantized helical edge modes.

[1]  J. Cai et al. Nature 622, 63 (2023).
[2] H. Park et al. Nature 622, 74 (2023).
[3] Y. Zeng, et al. Nature 622, 69 (2023).
[4] F. Xu, et al. PRX 13, 031037 (2023).
[5] Z. Lu, et al. Nature 626, 759 (2024).
[6] Y. Wang, et al. Nature 641, 1149 (2025).
[7] Y. Wang, et al. PRX, 16, 031009 (2026)

This lecture was made possible by the William C. Ferguson Fund.