Kavli Affiliate: Jie Shan
| First 5 Authors: Zhongdong Han, Zhongdong Han, , ,
| Summary:
Quantum spin Hall insulators (QSHIs) and excitonic insulators (EIs) are
prototypical topological and correlated states of matter, respectively. The
topological phase transition between the two has attracted much theoretical
interest but experimental studies have been hindered by the availability of
tunable materials that can access such a transition. Here, by utilizing the
interaction-enhanced g-factor and the flat moir’e bands in twisted bilayer
WSe2 (tWSe2), we realize tunable electron-like and hole-like Landau levels
(LLs) in the opposite valleys of tWSe2 under a perpendicular magnetic field. At
half-band-filling, which corresponds to electron-hole charge neutrality,
periodic oscillations between QSHIs (for fully filled LLs) and EIs (for
half-filled LLs) are observed due to the interplay between the cyclotron energy
and the intervalley correlation; QSHIs with up to four pairs of helical edge
states can be resolved. We further analyze the effect of Fermi surface nesting
on the stability of EIs via electric field-tuning of the moir’e band
structure. Our results demonstrate a novel QSHI-to-EI topological phase
transition and provide a comprehensive understanding of the fermiology of
tWSe2.
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