Special Quantum Matter Seminar

Van der Waals stacked two-dimensional materials has emerged as a rich platform for electron correlation and topology physics. Many efforts have been devoted to explore the moire superlattices of 2D materials. In this talk, I will introduce a family of crystalline materials, rhombohedral multilayer graphene, and discuss the opportunities in this largely uncharted material system. I will first show that one can obtain a quantum anomalous Hall effect (QAHE) with Chern number C = 5 by proximitizing it with spin-orbit-coupling from a WS2 layer. This approach of realizing QAHE is distinct from those in magnetic topological insulators and 2D moire superlattices. Then I will show our observation of the fractional QAHE when introducing a moire superlattice between pentalayer graphene and hBN. At zero magnetic field, we observed plateaus of quantized Hall resistance Rxy = h/(ve2), at moiré filling factors v = 1, 2/3, 3/5, 4/7, 4/9, 3/7 and 2/5. In addition, we observed Rxy =2h/e2 near v = 1/2 and it varies linearly as the filling factor is tuned—similar to the composite Fermi liquid (CFL) in the half-filled lowest Landau level at high magnetic fields. The rich family of FQAH and IQAH states in our high-quality graphene provide an ideal platform for exploring charge fractionalization and exotic quasiparticles for topological quantum computation.