4 p.m. - 5:15 p.m. Location: SLC 1.102
Dr. Congjun Wu (UC San Diego)
Orbital is a degree of freedom independent of charge and spin, which is characterized by spatial anisotropy and orbital degeneracy. It plays important roles in magnetism, super-conductivity, and transport in transition metal oxides. Recently, cold atom optical lattices have provided a new opportunity to investigate orbital physics. In this talk, we will present novel features of orbital physics that are not easily accessible in solid-state systems as below.
Bosons, as recently demonstrated in experiments, can be pumped into high orbital bands of optical lattices and stay with a long life-time. We will show that such metastable states of bosons exhibit a class of novel superfluid states with complex-valued wavefunc-tions spontaneously breaking time-reversal symmetry. They exhibit unconventional symmetries in analogy to unconventional superconductivity. These states are beyond the scope of the "no-node" theorem which applies to most well known states of bosons. For fermions, we will focus on the px,py-orbital bands of the honeycomb lattice, which exhibits fundamentally different properties from those in the pz-band system of graphene. The interesting physics here includes the flat-band structure and the associated strong correlation effects (e.g. Wigner crystal and ferromagnetism), orbital frustration, and quantum anomalous Hall states.