Abstract
There are three different types of nontrivial quantum disordered many-body phases: topological phase, stable gapless algebraic Bose liquid (ABL) phase, and symmetry protected topological (SPT) phase. There is no analogue of any of these three phases in classical physics. However, in this talk we will argue that although these phenomena are driven by strong quantum fluctuations, the nonlinear sigma models (NLSM) defined with semiclassical variables can still describe the ABL and SPT phase, as long as there is a topological term in the NLSM. In particular, using two different nonperturbative arguments, we will conclude that the existence of a topological Theta term can completely change the dynamics and spectrum of the quantum disordered phase, and drive the system into a stable gapless ABL phase. We will also find a large class of SPT phases in three and higher dimensions. Both lattice constructions and topological field theory descriptions for these phases will be discussed.
Coffee and tea will be served 20 minutes prior to the seminar.