Original Investigation of Topological Electronic Properties in Nigerian Mineral-Derived Van der Waals Heterostructures

Topological materials exhibiting protected surface electronic states arising from non-trivial band topology have emerged as one of the most actively investigated classes of quantum materials in condensed matter physics. Van der Waals heterostructures assembled from two-dimensional topological insulator layers offer tunable topological electronic properties through proximity effects and interlayer coupling. Nigerian mineral deposits in Plateau State and Nasarawa State include rare bismuth-bearing selenide and telluride minerals with structural analogs to the topological insulator family. This research conducts original investigations of the topological electronic properties of van der Waals heterostructures fabricated from exfoliated layers of naturally occurring and synthetically refined bismuth selenide derivatives incorporating Nigerian mineral precursors. Electronic band structure calculations using density functional theory with spin-orbit coupling incorporated via fully relativistic pseudopotentials are performed to predict topological invariants (Z2) and surface state dispersion for each identified compound. Mechanically exfoliated few-layer flakes are characterized by angle-resolved photoemission spectroscopy in collaboration with the National Synchrotron Light Source II at Brookhaven National Laboratory through an international research partnership, revealing the topological surface state Dirac cone with a measured Dirac point energy consistent with DFT predictions within 60 meV. Original contributions include the identification of a new compound in the bismuth-selenium-tellurium ternary phase diagram with predicted strong topological insulator character based on the calculated Z2 invariant and the first experimental ARPES characterization of this compound. The research establishes Nigerian mineral derivatives as a new source category for functional quantum material research. Keywords: topological insulator, van der Waals, electronic band structure, Nigerian minerals, photoemission