4 years ago

A Non-Natural Wurtzite Polymorph of HgSe: A Potential 3D Topological Insulator

A Non-Natural Wurtzite Polymorph of HgSe: A Potential 3D Topological Insulator
Sudhakar Pamidighantam, Prashant K. Jain, Progna Banerjee, Daniel Dumett Torres
This article demonstrates the power of topotactic synthesis coupled with density functional theory (DFT) for accessing and exploring new phases of matter. Naturally occurring HgSe is a semimetal with a zero gap. Unlike this natural zincblende form of HgSe, our DFT investigations predict that wurtzite HgSe has both an inverted band structure and a band gap, making it a 3D topological insulator (TI). Calculated band structures of HgxCd1–xSe alloys containing strongly relativistic Hg and weakly relativistic Cd show that band gap opening is a consequence of symmetry breaking resulting from a combination of crystal anisotropy and the scalar relativistic effect of Hg electrons. The relativistic contribution of Hg is significant enough in alloys with x ≥ 0.33 for achieving 3D TI behavior at room temperature. We experimentally realize the non-natural wurtzite form by topotactic ion exchange of wurtzite CdSe nanocrystals (NCs), which yields alloy NCs in the range x = 0–0.54 whose measured band gaps follow the predicted trend. We introduce crystal anisotropy as a new handle for expanding the classes of TI materials and also shed light on electronic principles in nanocrystalline alloys containing relativistic metals. NCs of this new wurtzite phase can become platforms for discovery of rich topological states and properties.

Publisher URL: http://dx.doi.org/10.1021/acs.chemmater.7b01674

DOI: 10.1021/acs.chemmater.7b01674

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