Observation of a transition from BCS to HTSC-like superconductivity in Ba1 ? x
KxBiO3 single crystals |
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Authors: | G É Tsydynzhapov A F Shevchun M R Trunin V N Zverev D V Shovkun N V Barkovskiy L A Klinkova |
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Institution: | (1) Institute of Solid State Physics, Russian Academy of Sciences, Chernogolovka, Moscow region, 142432, Russia |
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Abstract: | The temperature dependences of the upper critical field B c2(T) and surface impedance Z(T) = R(T) + iX(T) have been measured in Ba1 ? x KxBiO3 single crystals with transition temperatures 6 ≤ T c ≤ 32 K (0.6 > x > 0.4). A transition from the BCS to an unusual type of superconductivity has been revealed: B c2(T) curves of the crystals with T c > 20 K have positive curvature (as in some HTSCs), and those of the crystals with T c < 15 K described by the usual Werthamer-Helfand-Hohenberg (WHH) formula. The R(T) and X(T) dependences of the crystals with T c ≈ 32 K and T c ≈ 11 K in the temperature range T ? T c are linear (as in HTSCs) and exponential (BCS), respectively. The experimental results are discussed using the extended saddle point model by Abrikosov. |
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