物理系学术报告 Physics Department Colloquium
Nonperturbative effects of topological terms in Nonlinear sigma models and Gauge Theories
University of California at Santa Barbara
Topological terms can arise in condensed matter systems that involve topological fermion band structure. We will first discuss the effect of the topological Theta-terms of 2+1 dimensional nonlinear sigma models (NLSM). Using nonperturbative arguments, we conclude that the Theta term will strongly affect the disordered phase of this NLSM: when Theta = Pi, the disordered phase is either a gapless conformal field theory, or gapped and two fold degenerate. This gapless conformal field theory induced by the Theta term is a stable 2+1 dimensional algebraic spin liquid with power law correlations between physical quantities. We will also generalize this result to other NLSMs and gauge theories with the topological Theta term using a unified formalism.
Cenke Xu graduated from Tsinghua University with a Bachelor’s degree in 2003. In 2007 he received Ph.D. in physics from University of California, Berkeley. After that Cenke Xu joined Harvard University Society of Fellows as a Junior fellow. In 2009 Cenke Xu started his current position in UC Santa Barbara as an assistant professor. In the last one year Cenke Xu has received the Alfred P. Sloan Fellowship, and OCPA Outstanding Young Researcher Award. Cenke Xu’s research interests have been focusing on strongly correlated systems, especially the topological effects in strongly correlated systems.