Phenomenological correlations in high-temperature superconductors
  An interpretation of the quadratic parameter of the Ginzburg-Landau theory of superconductivity is presented in this paper. The negative term in the potential, which allows the spontaneous symmetry breaking, is interpreted as a direct contribution from the energy gap at the Fermi surface to the effective potential. As a result, in the London approximation of the Ginzburg-Landau theory for type-II superconductors, a strong correlation is predicted and observed between the upper critical field at zero kelvin and the critical temperature in high temperature superconductors. 
Miguel C. N. Fiolhais and Joseph L. Birman
cond-mat.supr-con