Superconductivity in (Ba,K)SbO3

Abstract

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.

Decisive Roles of Intersite Coulomb Interactions in Charge Ordered Systems

“…3 (c). For x=0 case, DFT-GGA shows the tilting instability in addition to the breathing instability while only the latter is observed in the experiment and our calculation with V , resulting in perfect fcc structure [24]. In addition, CDW phase survives up to higher doping of x 0.4 in DFT+U +V calculation, which is closer to the experimental phase boundary of x 0.5, due to the enhanced stretching instability by V .…”

“…In addition, CDW phase survives up to higher doping of x 0.4 in DFT+U +V calculation, which is closer to the experimental phase boundary of x 0.5, due to the enhanced stretching instability by V . We also note that the inclusion of V in BKBO enhances the hybridization between Bi and O atoms and that the breathing and stretching mode, which are the most important for SC, become softer by inclusion of V or Sb substitution, implying the enhancement of T c [24].…”

“…Perovskite BaBiO 3 (BBO) and BaSbO 3 (BSO) are prototypical CO materials that are not well understood by DFT-GGA and DFT+U [22][23][24][25][26][27][28][29][30][31][32][33][34]. They show CDW states characterized by breathing distortion of oxygen octahedra with the charge disproportionations of Bi ions [22][23][24]. The CDW is suppressed by substituting Ba with K and SC phase occurs at relatively higher transition temperature (T c ) [8,9].…”

“…At low-temperature, BBO has the monoclinic structure having oxygen octahedra with breathing distortion of displacement by δ B and small tilting angle of θ T between them as shown in Fig. 1(a), while BSO has δ B only, resulting in fcc structure (Fm 3m) [24]. To highlight the role of V , we investigate the artificial double-well potential induced by δ B without tilting [Fig.…”

Computational design of a new layered superconductor LaOTlF2

“…Note that the strong EPC and superconductivity in electron-doped LaOTlF 2 are associated with softening of acoustic phonons and Kohn anomaly, whereas in other related compounds such as (Ba,K)BiO 3 , 38,39 (Ba,K)SbO 3 , 40,41 hole-doped CsTlF 3 , 13 and La(O,F)BiS 2 , 8,11,42 the strong EPC and superconductivity are closely related to softening of optical phonon modes and a charge-density wave (CDW) instability. In particular, in LaO 0.5 F 0.5 BiS 2 , DFPT calculations suggest that there are four unstable phonon branches along the entire q = ( δ , δ , 0) line with the most unstable phonons at the M point.…”