Probing Correlated Integer and Fractional States in Twisted AB Bilayer MoS2 by Quantum Well Resonant Tunneling Spectroscopy

The observations of integer and fractional quantum anomalous Hall effects in transport measurements have established twisted bilayer TMDs as an exceptional platform for exploring correlated and topological quantum phenomena. However, the moiré inhomogeneity and the high sensitivity of transport properties to the displacement field demand high-quality device fabrications and motivate the development of more localized probing techniques.

Here, we report the observation of correlated integer and fractional insulating states near the conduction band edge in twisted AB-stacked bilayer MoS₂ (tMoS₂), using a dual-gate-tunable quantum-well resonant tunneling diode (QWRTD). In this setup, the probe few-layer graphene (FLG) measures the tunneling current (I) from tMoS₂ through a thin h-BN barrier, allowing us to obtain the probed conductivity (dI/dV). Together with the probe FLG, a bottom FLG beneath the tMoS₂ enables fine control of both the filling factor (ν) and displacement field (D) in tMoS₂.

At zero magnetic field, in the ν–D dependence of dI/dV, we observe a strong insulating state at ν = 1, and a fractional insulating state at ν = 3/4 emerging when D < −75 mV/nm. As the temperature increases, the ν = 3/4 state disappears around 10 K, whereas the ν = 1 state persists up to 100 K. Under a magnetic field, both insulating states show linear dispersions in the Landau fan diagram. Using the Streda formula, we extract nonzero Chern numbers, indicating that these are possible topologically nontrivial correlated states.

Our work demonstrates evidence of correlated integer and fractional insulating states in twisted AB bilayer MoS₂, showcasing a new probing method for studying strong correlations and topology, and introducing a promising new TMD moiré platform for such investigations.