Superconductivity in a unique type of copper oxide.
basic_science · Level V
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- Record sourced from PubMed, PMID 31109998.
- Also identified by DOI 10.1073/pnas.1900908116 and PMC identifier 6589659.
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Abstract
The mechanism of superconductivity in cuprates remains one of the big challenges of condensed matter physics. High-<i>T</i> <sub><i>c</i></sub> cuprates crystallize into a layered perovskite structure featuring copper oxygen octahedral coordination. Due to the Jahn Teller effect in combination with the strong static Coulomb interaction, the octahedra in high-<i>T</i> <sub><i>c</i></sub> cuprates are elongated along the <i>c</i> axis, leading to a 3<i>dx</i> <sup>2</sup>-<i>y</i> <sup>2</sup> orbital at the top of the band structure wherein the doped holes reside. This scenario gives rise to 2D characteristics in high-<i>T</i> <sub><i>c</i></sub> cuprates that favor <i>d</i>-wave pairing symmetry. Here, we report superconductivity in a cuprate Ba<sub>2</sub>CuO<sub>4-<i>y</i></sub> , wherein the local octahedron is in a very exceptional compressed version. The Ba<sub>2</sub>CuO<sub>4-<i>y</i></sub> compound was synthesized at high pressure at high temperatures and shows bulk superconductivity with critical temperature (<i>T</i> <sub><i>c</i></sub> ) above 70 K at ambient conditions. This superconducting transition temperature is more than 30 K higher than the <i>T</i> <sub><i>c</i></sub> for the isostructural counterparts based on classical La<sub>2</sub>CuO<sub>4</sub> X-ray absorption measurements indicate the heavily doped nature of the Ba<sub>2</sub>CuO<sub>4-<i>y</i></sub> superconductor. In compressed octahedron, the 3<i>d</i>3<i>z</i> <sup>2</sup>-<i>r</i> <sup>2</sup> orbital will be lifted above the 3<i>dx</i> <sup>2</sup>-<i>y</i> <sup>2</sup> orbital, leading to significant 3D nature in addition to the conventional 3<i>dx</i> <sup>2</sup>-<i>y</i> <sup>2</sup> orbital. This work sheds important light on advancing our comprehensive understanding of the superconducting mechanism of high <i>T</i> <sub><i>c</i></sub> in cuprate materials.