Direct magnetic imaging of fractional Chern insulators in twisted MoTe2

Abstract

Orbital magnetization provides a sensitive probe of topology and interactions, with particularly rich phenomenology in Chern insulators in which the topological edge states carry large equilibrium currents. Here we use a nanoscale superconducting sensor1,2 to map the magnetic fringe fields in twisted bilayers of MoTe2, in which transport3,4 and optical sensing5,6 experiments have revealed the formation of fractional Chern insulator (FCI) states at zero magnetic field. 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. We determine the local thermodynamic gaps of the most robust FCI state at ν = −2/3, finding −2/3Δ as large as 7 meV. We also characterize sample spatial disorder, which is dominated by both inhomogeneity in the effective unit cell area7 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 robust nature of the underlying correlated topological states. A nanoscale superconducting sensor used to map the magnetic fringe fields in twisted bilayers of MoTe2 shows the formation of fractional Chern insulator states at zero magnetic field.