Special QM Seminar Speaker Congjun Wu (UCSD) Tuesday, April 30

Time: 3:00 pm, Tuesday, April 30
Venue: CQCS (Ground floor/ 101 Campbell Hall)
Title: Orbital-active honeycomb materials
Abstract: We provide a unified view for a class of orbital-active honeycomb materials, including bismuthene, stanene, exciton-polarition lattice, and the recent focus of the twisted bilayer graphene. These materials are orbital-active possessing a pair of degenerate px and py orbitals on each site, which are unified under the E-representation of the C6v group symmetry. We started the research on orbital-active honeycomb systems in ultra-cold atom optical lattices, and found that similar physics also applies to the above solid state materials unified under the same symmetry structure. For solid state applications, we propose a new mechanism to boost the topological gap to the full scale of the atomic spin-orbit coupling, i.e., the order of 1eV. This mechanism has been recently realized in experiments of bismuthene on SiC, which shows the evidence of the gap up to 0.67eV. Mechanism for unconventional superconductivity assisted by the orbital structure in this class of materials is also studied. The flat band structure arises in 2D orbital-active honeycomb materials, such as organic metal frameworks and transition metal oxide films, in which strong correlation phenomena including Wigner crystallization and ferromagnetism appear.

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