| Time：1111207 (Wed.) 14:20~16:20 Speaker：Prof.蘇蓉容(Jung-Jung Su) 國立陽明交通大學電子物理學系/Department of Electrophysics, National Yang Ming Chiao Tung University Title：Quantum Anomalous Hall States in Bilayer Graphene Abstract：Quantum anomalous Hall effect Bernal stacked bilayer graphene has a collection of competing broken symmetry states characterized by flavor-dependent spontaneous valley polarization. The possible states include polarized and unpolarized orbital magnets and various quantum anomalous Hall states. By carefully evaluating the orbital magnetizations of the competing states, we find that the phase diagram is profoundly altered by a magic field by favoring states of which its natural filling factor υN is close to the actual filling factor, increasingly so as the magnetic field strengthens. We have explored how coupling of orbital magnetization to external magnetic fields is manifested in the dependence of ground state properties on weak gate electric fields and magnetic fields that favor particular states. We construct the ground-state phase diagram of this system, vs. gate-voltage and magnetic field at fixed carrier densities, and vs. gate-voltage and filling factor at fixed magnetic field, and obtain excellent agreement with two-point conductivity measurements. Our work explains why the υN = ±4 quantum Hall effect in bilayer graphene is stable to anomalously weak magnetic fields, and suggests that υN = ±2 anomalous quantum Hall effects could occur in the absence of a magnetic field in samples of sufficiently high quality. Place：S101, Gongguan Campus, NTNU |
