Data for Electronic transport across the insulator-metal transition in Co-doped pyrite FeS₂ single crystals

Pyrite FeS₂ is a low-cost, sustainable, non-toxic, 1-eV-band-gap semiconductor with unrealized potential in several application arenas, including photovoltaics. From the fundamental perspective, issues such as surface conduction and the deep-donor nature of S vacancies have hindered the study of low-temperature electronic phenomena in pyrite, including the insulator-metal transition (IMT). Here, we leverage a recently developed CoS₂-based contact scheme in tandem with wide-range doping via shallow Co donors to directly access low-temperature bulk FeS₂ transport properties and thus probe the IMT. Thoroughly characterized FeS₂:Co single crystals are studied over broad ranges of temperature (0.4 – 400 K) and Hall electron density (8.6 × 10¹⁶ – 2.0 × 10²⁰ cm⁻³) through resistivity, Hall effect, and magnetoresistance measurements. The IMT is found to occur near 2 × 10¹⁷ cm⁻³, with Efros-Shklovskii variable-range hopping below this, weak-localization-corrected metallic conductivity above this, and the onset of magnetic effects at the highest doping levels. Most significantly, unexpected additional phenomena are found in the vicinity of the IMT, including a non-linear Hall effect with non-monotonic temperature and doping dependence, and a non-saturating, linear positive magnetoresistance at low temperatures. Quantitative analysis of these phenomena points to unusually strong effect disorder effects in the vicinity of the IMT, further elucidating the electronic behavior of this unique semiconductor.