Browsing by Author "Das, Bhaskar"

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    Data for Electronic transport across the insulator-metal transition in Co-doped pyrite FeS₂ single crystals
    (2025-03-11) Das, Bhaskar; Voigt, Bryan; Moore, William; Lee, Yeon; Maiti, Moumita; Chaturvedi, Vipul; Haugstad, Greg; Manno, Michael; Aydil, Eray; Leighton, Chris; leighton@umn.edu; Leighton, Chris; Leighton Electronic and Magnetic Materials Lab; Department of Chemical Engineering and Materials Science, University of Minnesota
    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.
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    Data for Reexamination of the electronic phase diagram of doped NiS₂: Electronic, magnetic, and structural inhomogeneity across the Mott insulator-metal transition
    (2024-11-04) Tao, Yu; Das, Bhaskar; Calder, Stuart; Day-Roberts, Ezra; Maiti, Moumita; Lee, Yeon; Komar, Caitlyn; Birol, Turan; Leighton, Chris; leighton@umn.edu; Leighton, Chris; Leighton Electronic and Magnetic Materials Lab; Chemical Engineering and Materials Science, University of Minnesota
    Pyrite-structure NiS₂ is, in principle, a model antiferromagnetic Mott insulator that can be electron doped, hole doped, and bandwidth controlled. Despite decades of study, however, the electronic and magnetic behavior of NiS₂ have proven challenging to understand. Here, we build on recent advances establishing surface conduction in NiS₂ to completely reexamine the electronic phase behavior of electron- and hole-doped single-crystal Ni₁₋ₓCuₓS₂ and Ni₁₋ₓCoₓS₂. Magnetometry, heat capacity, neutron diffraction, and electronic transport measurements suggest that prior work missed vital details of the magnetic ordering in this system. While electron and hole doping rapidly increase the antiferromagnetic ordering temperature (by as much as 4-fold by x ≈ 0.1), signatures remain of antiferromagnetic and weak ferromagnetic ordering at the same temperatures as in undoped NiS₂. As these undoped ordering temperatures remain constant, the associated magnetic moments are diminished by doping, strongly implicating electronic/ magnetic phase coexistence across the Mott insulator-metal transition. Substantial structural changes and inhomogeneity accompany these evolutions, highlighting the importance of structural-chemical-electronic-magnetic coupling in NiS₂. The insulator-metal transition is also strongly electron/hole asymmetric, which we interpret with the aid of complementary dynamical mean-field theory results. These findings significantly revise and advance our understanding of the electronic phase behavior of this prototypical Mott insulator, highlighting the essential role of electronic, magnetic, structural, and chemical inhomogeneity across the Mott transition. This dataset contains all digital data in the published paper of the same name.