Yiping Wang, Gillian E. Minarik, Weijie Li, Yves Kwan, Shuai Yuan, Eric Anderson, Chaowei Hu, Julian Ingham, Jeongheon Choe, Takashi Taniguchi, Kenji Watanabe, Xavier Roy, Jiun-Haw Chu, Raquel Queiroz, James C. Hone, N. Regnault, Xiaodong Xu, Xiaoyang Zhu
The interplay among electronic correlation, topology, and time-reversal symmetry often leads to exotic quantum states of matter, as highlighted by the discoveries of fractional Chern insulators in twisted bilayer MoTe 2 ( tMoTe 2 ) . Among the fractional Chern insulators (FCIs) in tMoTe 2 , the most robust is at a hole filling factor of ν = − 2 3 per moiré unit cell. Here, employing pump-probe circular dichroism measurement on tMoTe 2 at twist angles θ = 3.9 ° and 3.7°, we show that a correlated state at ν = − 4 3 exhibits an unusual Ising antiferromagnet behavior. The ν = − 4 3 state with no net magnetization undergoes first order phase transitions at extremely low magnetic fields of | μ 0 H | ∼ 2 – 6 mT to partially valley polarized states. This behavior is notably absent for all other correlated states in tMoTe 2 and also disappears for ν = − 4 3 at higher or lower twist angles ( θ = 4.0 ° or 3.3°). 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 that reveal the extreme closeness in energy ( Δ E < 1 meV ) between the putative FTI ( ν ± = − 2 3 and ν ∓ = − 2 3 ) and partially valley polarized states ( ν ± = − 1