Anomalous magnetic field dependence of the thermodynamic transition line in the isotropic superconductor (K, Ba)BiO3 -: art. no. 177201

Thermodynamic (specific heat, reversible magnetization, tunneling spectroscopy) and transport measurements have been performed on high quality (K, Ba)BiO3 single crystals. The temperature dependence of the magnetic field H-Cp corresponding to the onset of the specific heat anomaly presents a clear positive curvature. H-Cp is significantly smaller than the field H-Delta for which the superconducting gap vanishes but is closely related to the irreversibility line deduced from transport data. Moreover, the temperature dependence of the reversible magnetization presents a strong deviation from the Ginzburg-Landau theory emphasizing the peculiar nature of the superconducting transition in this material.