Pressure-Induced Superconductivity and Flattened Se₆ Rings in the Wide Band Gap Semiconductor Cu₂I₂Se₆
2019
Cai, Weizhao | Lin, Wenwen | Li, Long-Hua | Malliakas, Christos D. | Zhang, Rong | Groesbeck, Matthew | Bao, Jin-Ke | Zhang, Dongzhou | Sterer, Eran | Kanatzidis, Mercouri G. | Deemyad, Shanti
The two major classes of unconventional superconductors, cuprates and Fe-based superconductors, have magnetic parent compounds, are layered, and generally feature square-lattice symmetry. We report the discovery of pressure-induced superconductivity in a nonmagnetic and wide band gap 1.95 eV semiconductor, Cu₂I₂Se₆, with a unique anisotropic structure composed of two types of distinct molecules: Se₆ rings and Cu₂I₂ dimers, which are linked in a three-dimensional framework. Cu₂I₂Se₆ exhibits a concurrent pressure-induced metallization and superconductivity at ∼21.0 GPa with critical temperature (Tc) of ∼2.8 K. The Tc monotonically increases within the range of our study reaching ∼9.0 K around 41.0 GPa. These observations coincide with unprecedented chair-to-planar conformational changes of Se₆ rings, an abrupt decrease along the c-axis, and negative compression within the ab plane during the phase transition. DFT calculations demonstrate that the flattened Se₆ rings within the CuSe layer create a high density of states at the Fermi level. The unique structural features of Cu₂I₂Se₆ imply that superconductivity may emerge in anisotropic Cu-containing materials without square-lattice geometry and magnetic order in the parent compound.
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