Direct magnetic imaging of fractional Chern insulators in twisted MoTe2

In the absence of time reversal symmetry, orbital magnetization provides a
sensitive probe of topology and interactions, with particularly rich
phenomenology in Chern insulators where topological edge states carry
large equilibrium currents. Here, we use a nanoscale superconducting
sensor to map the magnetic fringe fields in twisted bilayers of MoTe2,
where transport and optical sensing experiments have revealed the
formation of fractional Chern insulator (FCI) states at zero magnetic
field. At a temperature of 1.6K, 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,
finding −2/3Δ 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 dipole moment. Our results highlight both
the challenges posed by structural disorder in the study of twisted
homobilayer moiré systems and the opportunities afforded by the remarkably
robust nature of the underlying correlated topological states.