Large oxygen-isotope effect in Sr0.4K0.6BiO3: Evidence for phonon-mediated superconductivity
Abstract
Oxygen-isotope effect has been investigated in a recently discovered superconductor Sr0.4K0.6BiO3. This compound has a distorted perovskite structure and becomes superconducting at about 12 K. Upon replacing 16O with 18O by 60-80%, the Tc of the sample is shifted down by 0.32-0.50 K, corresponding to an isotope exponent of alphaO = 0.40(5). This isotope exponent is very close to that for a similar bismuthate superconductor Ba1-xKxBiO3 with Tc = 30 K. The very distinctive doping and Tc dependencies of alphaO observed in bismuthates and cuprates suggest that bismuthates should belong to conventional phonon-mediated superconductors while cuprates might be unconventional supercondutors.
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