Topological semimetals are characterized by topologically protected band-structure nodes, such as Weyl points. These band nodes can be understood as momentum-space analogs of topological defects. However, although notions associated with topological defects have been systematically studied since 1970s, many of the phenomena have not been considered in the context of band-structure nodes. In this presentation, I will further elaborate on the analogy between band nodes and topological defects by two examples: momentum-space analogs of boojums and of Alice strings.
The talk consists of two parts. In the first part we show that band nodes occurring on high-symmetry planes are analogous to boojums, i.e. topological defects bound to the surface of an ordered medium. By exploiting this similarity, we identify rules for converting generic nodes to nodes in high-symmetry planes (and vice versa). In the second part of the talk, we show that exceptional lines in non-Hermitian band structures act as Alice strings. This is manifested by the reversal of the topological charge of a node, if it is braided around an exceptional line.
The Zoom link will be sent to the Graduate Student and PDRA mailing lists. If you are not on one of those lists and are interested in attending, please email Mark Hirsbrunner at hrsbrnn2@illinois.edu for the link.
