Twist-angle-dependent quantum phase diagrams in moiré bilayer MoTe2

What it is

Stacking two atom-thin semiconductor sheets at a small angle makes a moiré superlattice, a highly tunable platform for strongly correlated and topological quantum phases, and twisted bilayer MoTe2 is known to host fractional topological phases with no magnetic field applied. How those phases change with twist angle, and how they compete with other correlated states, was largely unexplored. The authors report a systematic transport study of twist-angle-dependent phase diagrams across 3.79° to 5.76°, finding an evolution from valley-polarized fractional topological states to valley-degenerate correlated states and superconductivity. At relatively small angles, partially filled Chern bands host fractional quantum anomalous Hall states following the Jain sequence, with signatures of an anomalous composite Fermi liquid at half a hole per moiré cell. Increasing the angle suppresses the fractional phases and reconstructs the half-filled band into symmetry-breaking integer Chern insulating states. At one hole per moiré cell they see a transition from robust integer quantum anomalous Hall insulators at small angles to topologically trivial correlated insulators, tuned by displacement field, at larger angles. Above about 5.6°, superconductivity emerges next to that correlated insulator, with a phase diagram closely resembling recent reports in twisted bilayer WSe2.