Ben Gurion University, Israel
Title: Spin-orbit interaction and topological states in spin 3/2 cold atomic gas
Biography: Yshai Avishai
The feasibility of manipulating a Fermi gas of cold atoms with spin s>1/2 in a specially designed optical potential enables studying a new kind of topological insulators, described by a two band model where cold fermionic atoms with spin s=3/2 occupy a two dimensional optical lattice where spin orbit coupling is relevant. The pertinent time-reversal invariant Hamiltonian is an 8x8 matrix in [spin]x[particle-hole] spaces, whose spectrum and topological properties are remarkably distinct from those encountered for spin 1/2 fermions. Specifically, on each edge of the 2D sample there are two pairs of oppositely propagating helical states. The two states in each pair move along the same direction, but they are protected against scattering with each other: they have different quantum numbers and different dispersion: (E1 proportional to k and E2 proportional to k^3). Strikingly, the corresponding bulk topological numbers are Z1=2 and Z2=0. Thus, the ubiquitous bulk-edge correspondence is broken here because the group velocity (and hence the conductivity) associated with the second edge state vanishes at k=0.