Anomalous magnetic field dependence of the thermodynamic transition line   in the isotropic superconductor (K,Ba)Bi03
  Thermodynamic (specific heat, reversible magnetization, tunneling spectroscopy) and transport measurements have been performed on high quality (K,Ba)BiO$_3$ 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 present a strong deviation from the Ginzburg--Landau theory emphasazing the peculiar nature of the superconducting transition in this material. 
S.Blanchard, T.Klein, J.Marcus, I.Joumard, A.Sulpice, P.Szabo,   P.Samuely, A.G.M.Jansen and C.Marcenat