UW–Madison R. G. Herb Condensed Matter Seminar: Yihang Zeng, Cornell University

Chern insulators, which are the lattice analogs of the quantum Hall states, can potentially manifest high-temperature topological orders at zero magnetic field to enable next-generation topological quantum devices. To date, integer Chern insulators have been experimentally demonstrated in several systems at zero magnetic field, but fractional Chern insulators have been reported only in graphene-based systems under a finite magnetic field. The emergence of semiconductor moiré materials, which support tunable topological flat bands, opens a new opportunity to realize fractional Chern insulators. In this talk, I will present evidence for both integer and fractional Chern insulators at zero magnetic field in small-angle twisted bilayer MoTe2. Combining our newly developed local electronic compressibility measurement and magneto-optical measurement, we find the system is incompressible and spontaneously breaks time reversal symmetry at hole filling factor 1 and 2/3. We show that they are integer and fractional Chern insulators, respectively, from their dispersion in filling factor with applied magnetic field. I will further demonstrate electric-field-tuned topological phase transitions involving the Chern insulators. Our findings pave the way for demonstration of quantized fractional Hall conductance and anyonic excitation and braiding in semiconductor moiré materials.

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