Observation of the fractional quantum spin Hall effect in moiré MoTe2

Kavli Affiliate: Jie Shan

| First 5 Authors: Kaifei Kang, Bowen Shen, Yichen Qiu, Kenji Watanabe, Takashi Taniguchi

| Summary:

Quantum spin Hall (QSH) insulators are two-dimensional electronic materials
that have a bulk band gap like an ordinary insulator but have topologically
protected pairs of edge modes of opposite chiralities. To date, experimental
studies have found only integer QSH insulators with counter-propagating
up-spins and down-spins at each edge leading to a quantized conductance
G0=e^2/h. Here we report transport evidence of a fractional QSH insulator in
2.1-degree-twisted bilayer MoTe2, which supports spin-Sz conservation and flat
spin-contrasting Chern bands. At filling factor v = 3 of the moir’e valence
bands, each edge contributes a conductance 3/2 G0 with zero anomalous Hall
conductivity. The state is likely a time-reversal pair of the even-denominator
3/2-fractional Chern insulators. Further, at v = 2, 4 and 6, we observe a
single, double and triple QSH insulator with each edge contributing a
conductance G0, 2G0 and 3G0, respectively. Our results open up the possibility
of realizing time reversal symmetric non-abelian anyons and other unexpected
topological phases in highly tunable moir’e materials.

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