Direct magnetic imaging of fractional Chern insulators in twisted MoTe$_2$ with a superconducting sensor

TL;DR

This study employs a superconducting sensor to directly image magnetic fields in twisted MoTe2, revealing fractional Chern insulator states and their properties at zero magnetic field, advancing understanding of topological moiré systems.

Contribution

First direct magnetic imaging of fractional Chern insulators in twisted MoTe2, providing quantitative magnetization data and insights into disorder effects in these topological states.

Findings

Detected magnetic oscillations at specific fillings indicating FCI formation

Measured local thermodynamic gaps up to 7 meV for the FCI state at ν=-2/3

Mapped the magnetic phase diagram revealing disorder sources

Abstract

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 MoTe$_2$, 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 $\nu=-1,-2/3,-3/5,-4/7$ and $-5/9$ of the first moir\'e 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 $\nu=-2/3$, finding $^{-2/3}\Delta$ 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 moir\'e systems and the opportunities afforded by the remarkably robust nature of the underlying correlated topological states.