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Abstract:
Spin-orbit coupled materials have attracted revived prominent research interest as of late, especially due their connection with topological materials. A hallmark of this pursuit is arguably formed by the advent of topological band insulators (TBIs). Whereas such topological systems are often characterized by the presence of metallic edge states, we here provide a review on the equally rich, although far less explored, aspects of the bulk. Starting from the fact that pi fluxes unambiguously probe the nontrivial nature of time reversal invariant TBIs upon binding special excitations, we summarize the criteria for the formation of similar localized modes in the presence of crystal dislocations. These criteria under which dislocations act as effective fluxes directly relate to their status as unique probes of translational symmetry breaking and as such pinpoint an indexing of TBIs beyond the standard tenfold way. Apart from elucidating refined classification schemes that include crystal symmetries, we also review why the predicted dislocation physics may be perceived compelling in its own right. For example, the study of these defects could result in new routes to explore spin-charge separated excitations. Similarly, arrays of dislocations, as realizable in ordinary grain boundaries, can be shown to host self organized semimetals that have distinct transport properties. Most importantly, however, research efforts on the material side as well as recent experimental signatures further indicate that the outlined perspective can very well provide for an attractive, timely and experimentally viable research agenda beyond the edge state focussed activities.
