Superconducting bismuthates (Ba,K)BiO3 (BKBO) constitute an interesting class of superconductors in that superconductivity with a remarkably high Tc of 30 K arises in proximity to charge density wave (CDW) order. Prior understanding on the driving mechanism of the CDW and superconductivity emphasizes the role of either bismuth (negative U model) or oxygen ions (ligand hole model). While holes in BKBO presumably reside on oxygen owing to their negative charge transfer energy, so far there has been no other comparative material studied. Here, we introduce (Ba,K)SbO3 (BKSO) in which the Sb 5s orbital energy is higher than that of the Bi 6s orbitals enabling tuning of the charge transfer energy from negative to slightly positive. The parent compound BaSbO3−δ shows a larger CDW gap compared to the undoped bismuthate BaBiO3. As the CDW order is suppressed via potassium substitution up to 65 %, superconductivity emerges, rising up to Tc = 15 K. This value is lower than the maximum Tc of BKBO, but higher by more than a factor of two at comparable potassium concentrations. The discovery of an enhanced CDW gap and superconductivity in BKSO indicates that the sign of the charge transfer energy may not be crucial, but instead strong metal-oxygen covalency plays the essential role in constituting a CDW and high-Tc superconductivity in the main-group perovskite oxides.
@article{arxiv.2107.06596,
title = {Discovery of Superconductivity in (Ba,K)SbO$_{3}$},
author = {Minu Kim and Graham M. McNally and Hun-Ho Kim and Mohamed Oudah and Alexandra Gibbs and Pascal Manuel and Robert Green and Tomohiro Takayama and Alexander Yaresko and Ulrich Wedig and Masahiko Isobe and Reinhard K. Kremer and D. A. Bonn and Bernhard Keimer and Hidenori Takagi},
journal= {arXiv preprint arXiv:2107.06596},
year = {2022}
}