Local imaging of ferromagnetism and topology in twisted bilayer MoTe2

Bilayer MoTe2 has been recently shown to host Fractional Chern Insulators at zero magnetic field. Here, we use a nanoscale superconducting sensor to map the magnetic fringe fields in twisted bilayers of MoTe2. In the twist angle range from 3.5 to 3.9 degrees, we observe oscillations in the local magnetic field associated with fillings ν=−1,−2/3,−3/5,−4/7 and −5/9 of the first moiré hole band, consistent with the formation of FCIs at these fillings. By quantitatively reconstructing the magnetization, we determine the local thermodynamic gaps of the most robust FCI state at ν=−2/3 to be as large as 7 meV. Spatial mapping of the charge density- and displacement field-tuned magnetic phase diagram further allows us to characterize sample disorder, which we find to be dominated by both inhomogeneity in the effective unit cell area as well as inhomogeneity in the band edge offset and bound electric dipole moment.

For smaller twist angles ranging from 2.1 to 2.7 degrees, we observe FCIs in a similar sequence, albeit with reduced gap size. We also observe a ferromagnetic signal associated with a state at v=-3. We discuss these results in the context of recent theoretical and experimental literature concerning the nature of correlated and topological phases in this system.