Magnetism and superconductivity in topotactically modified transition metal chalcogenides

Abstract

Inspired by the structure of the simplest iron-based chalcogenide superconductor, FeSe, the class of tetrahedral transition metal chalcogenides (TTMCs) exhibit interesting chemical and physical properties due to its structure. This structure consists of tetrahedrally coordinated transition metal chalcogenides stacked to form two dimensional layers held together by van der Waals forces. This structure and its associated tetrahedral coordination of transition metal to chalcogenide, square transition metal sublattice, van der Waals layered structure, and d-electron filling at the Fermi level yields interesting properties from superconductivity to frustrated itinerant magnetism. In this dissertation work, we demonstrate that the anti-PbO type FeCh (Ch = S, Se, Te) structure offers a perfect platform for the study of superconductivity in the iron-based system as well as new physics as the class is expanded to different transition metals. Prior to this work, the binaries of the TTMC family was limited to iron, but has been expanded to cobalt. In the cobalt compound, CoSe, superconductivity in the FeSe binary is suppressed and a frustrated spin glass like magnetic state emerges. Beyond the binaries, we have shown that topotactic hydrothermal synthetic routes on the iron chalcogenide system can lead to novel intercalated phases where long range magnetic order can co-exist with superconductivity in the (LiOH)FeSe system. This synthetic scheme also allows the intercalation of organic molecules, specifically ethylenediamine, to form organic-inorganic hybrids which can offer a new avenue for designing heterolayer compounds with complex interlayer interactions and bonding.