Tonghang Han: Chiral Superconductivity and Fractional Quantum Anomalous Hall Effect in Rhombohedral Graphene

Chiral superconductivity and fractional quantum anomalous Hall effect in rhombohedral graphene

Abstract: Exotic quantum phenomena can emerge from the interplay of electron correlations and nontrivial topology, such as fractional quantum Hall effects and topological superconductivity. Rhombohedral multilayer graphene, with its gate-tunable flat bands and Berry curvature, provides a pristine crystalline platform for exploring these emergent phenomena. Here, I present our observation of the fractional quantum anomalous Hall effect (FQAHE) in a rhombohedral graphene/hBN moiré superlattice, and new developments including v=1/3 FQAHE, thermodynamic compressibility of fractional Chern insulators, and extended QAH state. I will also discuss the discovery of chiral superconductivity in rhombohedral 4-, 5-, and 6-layer graphene without the moiré effect. In the normal state, we observe an anomalous Hall effect and magnetic hysteresis that persists below the superconducting transition temperature, indicating time-reversal symmetry breaking at the orbital level.