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Electron correlation and topology in crystalline rhombohedral Graphene

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 our observation of correlated insulator and orbital multiferroicity in pentalayer rhombohedral graphene. Then I will 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. Lastly, I will show our observation of the fractional QAHE when introducing a moire superlattice between pentalayer graphene and hBN. FQAHE is the analog of the fractional quantum Hall effect at zero magnetic field, is predicted to exist in topological flat bands under spontaneous time-reversal-symmetry breaking. 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.

Host: Sergio de la Barrera/Yong Baek Kim
Event series  Toronto Quantum Matter Seminars