Title: Chemical Bonds in Topological Materials
Abstract: Topological materials are solid-state compounds that have atypical charge carriers, often acting analogously to particles in high-energy physics. They are significant for both fundamental and applied science, with potential uses in spintronics, catalysis, and quantum information science. But despite the great promise of this field, the majority of known topological materials conform to the same handful of structure types. By utilizing chemical principles, we can design and discover new topological materials and investigate their unusual charge transport and magnetism.
In the first half of my talk, I will focus on synthetic routes to new subchalcogenide topological semimetals. Subchalcogenides are a hybrid class of materials between intermetallics and chalcogenides, containing both metal-metal and metal-chalcogenide interactions. Their diverse bonding character leads to quasi-lower-dimensional metallic substructures, which have greater potential for electron-electron interactions. The subchalcogenides Ir2In8Q (Q = S, Se, Te) are a newly reported family of Dirac semimetals, with large, anistropic magnetoresistance and high charge carrier mobility characteristic of a topological semimetals. In addition, Ir2In8Se and Ir2In8Te have re-entrant structural modulation, likely due to electronic instabilities in their band structures. This family of compounds offer a new platform for probing the interactions of electronic instabilities and topology, along with expanding the known library of topological structures.
In the second half of my talk, I will discuss hypervalent (electron-rich) chemical bonding as a design principle for new topological semimetals, with a focus on quasi-one-dimensional hypervalent Bi chains. Delocalized, electron-rich bonding has been shown to be an effective design principle to find new topological square-net materials, with band inversion occurring at the Fermi level of compounds with the ideal electron count and number of atoms in the unit cell. I will discuss how the Ln3MPn5 (Ln = lanthanide; M = transition metal; Pn = pnictide) family is also topological, and how the interactions of quasi-one-dimensional Pn2- chains with the rest of the structure create a complex, anisotropic electronic structure. Through these synthetic and bonding approaches to identifying new topological materials, we show that chemists play a vital role in advancing the field.
