One-dimensional conduction channels in the correlated Mott NiS₂ arising from obstructed Wannier charges.

Abstract

NiS₂, a material long recognized for its non-collinear magnetic order and correlated insulating behavior, has until now been entirely overlooked as a potential host of topological phenomena. Bulk NiS₂ is known to be a Mott or charge-transfer insulator, yet its surface exhibits anomalous finite conductivity of unclear origin. Additionally, a definitive consensus regarding its low-temperature magnetic transition remains elusive. In this work, we provide a unified explanation for both of these longstanding puzzles. First, we present a refined characterization of NiS₂'s magnetic phases by proposing a novel ground state based on a rigorous symmetry analysis of high-resolution neutron scattering data. Second, through high-resolution scanning tunneling microscopy and spectroscopy (STM/STS), we reveal the presence of robust edge states on both Ni- and S-terminated surfaces, which persist even under applied magnetic fields. Using ab initio calculations combined with topological analysis, we attribute these edge states to obstructed atomic charges arising from the bulk's obstructed nature. Altogether, this study not only sheds new light on the physics of NiS₂, but also establishes a solid experimental and theoretical foundation for exploring the interplay between topology and electronic correlations.