Electronic correlations and chiral, nonlocal transport in surface states of HfNiSn single crystals

Topological insulators (TI), with metallic surface or edge states that are protected against backscattering, could see applications in low-power electronics and spintronics. In most TI identified to date, the valence and conduction band appear in reverse order compared to an equivalent monoatomic insulator. Here, we explore a different route towards topologically nontrivial states that may arise from metallic surface states in topologically trivial bulk insulators without such band inversion. We present first experimental work on high-quality single crystals of HfNiSn, where magnetotransport measurements show surface transport with weak anti-localization, consistent with a metallic surface state showing strong spin-orbit coupling, and nonlinear I(V) characteristics that indicate electronic correlations. A nonlocal transport component that violates Onsager reciprocity could imply chiral edge state conduction, qualitatively similar to quantum Hall edge states, yet in the absence of external magnetic fields. Common energy scales for electronic correlations and other transport anomalies suggest that the correlations themselves may play a decisive role in creating a topologically nontrivial state on the HfNiSn surface.