Conduction through subsurface cracks in bulk topological insulators

TL;DR

This study shows that subsurface cracks in the topological insulator SmB₆ enhance electrical conduction by creating additional conductive paths, supporting its topological nature and relevance to other TIs with defects.

Contribution

Demonstrates that subsurface cracks in SmB₆ increase electrical conduction, providing experimental evidence for the conductive role of defects in topological insulators.

Findings

Cracks in SmB₆ increase electrical conduction.

Cracks act as additional conductive topological surfaces.

Results support the topological nature of SmB₆.

Abstract

Topological insulators (TIs) have the singular distinction of being electronic insulators while harboring metallic, conductive surfaces. In ordinary materials, defects such as cracks and deformations are barriers to electrical conduction, intuitively making the material more electrically resistive. Peculiarly, 3D TIs should become better conductors when they are cracked because the cracks themselves, which act as conductive topological surfaces, provide additional paths for the electrical current. Significantly, for a TI material, any surface or extended defect harbors such conduction. In this letter, we demonstrate that small subsurface cracks formed within the predicted 3D TI samarium hexaboride (SmB$_{6}$) via systematic scratching or sanding results in such an increase in the electrical conduction. SmB$_{6}$ is in a unique position among TIs to exhibit this effect because its single-crystals are thick enough to harbor cracks, and because it remarkably does not appear to suffer from conduction through bulk impurities. Our results not only strengthen the building case for SmB$_{6}$'s topological nature, but are relevant to all TIs with cracks, including TI films with grain boundaries.