Past Events

Abstract
 

Doubtlessly, topological insulators and superconductors as well as graphene are two most exciting and attracting fields in condensed matter physics in the most recent decade. In consequence, as the combination of these two, topological semi-metals, which on the one hand show unconventional band structures similarly to graphene, on the other also topologically non-trivial, have gained mass attention in the past few years. For instance, Weyl semi-metals, the most well-known example of two-dimensional topological semi-metals, have shown not only rich physics but many novel observable properties. And it is noteworthy that the unconventional transport properties of topological semi-metals are robust against disorders, and the stabilities are ensured by the topological non-triviality in a manner which is exactly the same as how those surface states are protected by topology in the case of topological insulators and superconductors.

In this work, theoretical theories of topological semi-metals in both even-dimensional, chiral-symmetry-preserving and odd-dimensional chiral-symmetry-breaking cases are going to be formulated. To be specific, in presence of disorder, an anisotropic topological term would emerge in both the action of non-linear sigma model and effective response action subjected to an external U(1) gauge field. In the language of both non-linear sigma model and gauge theory, the two types of anisotropic topological terms of topological semi-metals in any dimensions are going to be derived and discussed. In addition, the relationship between topological semi-metals and topological insulators and superconductors or fermions in field theory are going to be revealed as well.

Anyone interested is welcome to attend.