Fig. 3. Magnetic-field tuned Chern insulator.

a Magnetic circular dichroism (MCD) as a function of moiré lattice filling factor $\nu$ and out-of-plane magnetic field $B$ under zero electric field. Top: filling factor dependence of magnetic susceptibility χ extracted from the small-field MCD. b Magnetic-field dependence of the normalized MCD for representative filling factors around one (solid lines, left axis) and the derivative of MCD for $\nu =1$ (dashed red line, right axis). MCD reaches 85% of the fully saturated value (dashed lines) at the saturation field $B_s$. c Spectrally integrated optical reflection contrast (RC) of the sensor 2 s exciton as a function of $\nu$ and $B$. The dashed lines show the expected dispersion for states with Chern number C = 0 and 1 near $\nu$ = 1. Top: line cut at the highest field of $B=8.75$ T. The dotted line in (a, c) denotes the saturation field $B_s$. d Calculated electronic density of states (DOS) as a function of $\nu$ and $B$ showing Zeeman splitting of the van Hove singularity (vHS, dashed lines). All measurements were performed at 1.6 K. All results are for 2.7° twisted WSe₂.