Local inversion-symmetry breaking in a bismuthate high-T<sub>c</sub> superconductor.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 36792582.
- Also identified by DOI 10.1038/s41467-023-36348-9 and PMC identifier 9931700.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
The doped perovskite BaBiO<sub>3</sub> exhibits a maximum superconducting transition temperature (T<sub>c</sub>) of 34 K and was the first high-T<sub>c</sub> oxide to be discovered, yet pivotal questions regarding the nature of both the metallic and superconducting states remain unresolved. Although it is generally thought that superconductivity in the bismuthates is of the conventional s-wave type, the pairing mechanism is still debated, with strong electron-phonon coupling and bismuth valence or bond disproportionation possibly playing a role. Here we use diffuse x-ray scattering and Monte Carlo modeling to study the local structure of Ba<sub>1-x</sub>K<sub>x</sub>BiO<sub>3</sub> across its insulator-metal boundary. We find no evidence for either long- or short-range disproportionation, which resolves a major conundrum, as disproportionation and the related polaronic effects are likely not relevant for the metallic and superconducting states. Instead, we uncover nanoscale structural correlations that break inversion symmetry, with far-reaching implications for the electronic physics. This unexpected finding furthermore establishes that the bismuthates belong to the broader classes of materials with hidden spin-orbit coupling and a tendency towards inversion-breaking displacements.