Speaker
Robert-Jan Slager
Description
Semi-metals are characterized by nodal band structures that
give rise to exotic electronic properties. The stability of Dirac
semi-metals, such as graphene in two spatial dimensions
(2D), requires the presence of lattice symmetries, while akin
to the surface states of topological band insulators, Weyl
semi-metals in three spatial dimensions (3D) are protected
by band topology. I will show that in the bulk of topological
band insulators, self-organized topologically protected semi-
metals can emerge along a grain boundary, a ubiquitous
extended lattice defect in any crystalline material. In addition
to experimentally accessible electronic transport
measurements, these states exhibit a valley anomaly that
influences the edge spin transport in two spatial dimensions
(2D), whereas in 3D they appear as graphene-like states that
should exhibit an odd-integer quantum Hall effect. The
general mechanism underlying these novel semi-metals,
being the hybridization of spinon modes bound to the grain
boundary, suggests that topological semi-metals can emerge
in any topological material where lattice dislocations bind
localized topological modes.