Kavli Affiliate: Jie Shan
| First 5 Authors: Kaifei Kang, Yichen Qiu, Bowen Shen, Kihong Lee, Zhengchao Xia
| Summary:
Twisted bilayer transition metal dichalcogenide semiconductors, which support
flat Chern bands with enhanced interaction effects, realize a platform for
fractional Chern insulators and fractional quantum spin Hall (FQSH) insulators.
A recent experiment has reported the emergence of a FQSH insulator protected by
spin-Sz conservation at a moir’e lattice filling factor {nu}=3 in 2.1-degree
twisted bilayer MoTe2. Theoretical studies have proposed both time-reversal
symmetric and asymmetric ground states as possible candidates for the observed
FQSH insulator, but the nature of the state remains unexplored. Here we report
the observation of spontaneous time-reversal symmetry breaking at generic
fillings in 2.1-degree twisted bilayer MoTe2 from {nu}<1 all the way to
{nu}>6 except at {nu}=2, 4, and 6. Although zero Hall response is observed at
{nu}=3 for magnetic fields higher than 20 mT, a finite anomalous Hall response
accompanied by a magnetic hysteresis is observed at lower magnetic fields,
demonstrating spontaneous time-reversal symmetry breaking. Our work shows the
tendency towards ferromagnetism by doping the first three pairs of conjugate
Chern bands in the material; it also sheds light on the nature of the FQSH
insulator at {nu}=3.
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