Abstract
(Ba,K)BiO3 constitute an interesting class of superconductors, where the remarkably high superconducting transition temperature Tc of 30 K arises in proximity to charge density wave order. However, the precise mechanism behind these phases remains unclear. Here, enabled by high-pressure synthesis, we report superconductivity in (Ba,K)SbO3 with a positive oxygen–metal charge transfer energy in contrast to (Ba,K)BiO3. The parent compound BaSbO3−δ shows a larger charge density wave gap compared to BaBiO3. As the charge density wave 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 (Ba,K)BiO3, but higher by more than a factor of two at comparable potassium concentrations. The discovery of an enhanced charge density wave gap and superconductivity in (Ba,K)SbO3 indicates that strong oxygen–metal covalency may be more essential than the sign of the charge transfer energy in the main-group perovskite superconductors.
Highlights
Superconducting bismuthates, BaPb1–xBixO3 (BPBO)[1] and Ba1– xKxBiO3 (BKBO)[2,3], have attracted considerable research interest since their discovery more than three decades ago
As the charge density wave (CDW) order is suppressed via chemical substitution of Bi with Pb or Ba with K, the compounds become superconducting up to a maximum Tc of 12 K in BPBO, and 30 K in BKBO
The importance of oxygen holes has previously been demonstrated in the Zhang–Rice model[28] for cuprates, in which holes on the copper and oxygen sites form a strongly hybridized singlet state, highlighting their potential role in understanding the CDW order and high-Tc superconductivity in the bismuthates as well
Summary
Superconducting bismuthates, BaPb1–xBixO3 (BPBO)[1] and Ba1– xKxBiO3 (BKBO)[2,3], have attracted considerable research interest since their discovery more than three decades ago. As the CDW order is suppressed, oxygen holes become delocalized, giving rise to superconductivity, possibly via strong electron–phonon coupling[21,27].
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