Critical fluctuations in high-Tcsuperconductors

The Ginzburg criterion suggests that the Ginzburg-Landau theory will break down within ∼0.1 K of the transition temperature of the new high-$T_c$ superconductors. Theoretical consequences of this include a weak divergence in the specific heat at $T_c$, and a correlation length which diverges as ${(T-T_c)}^{-\nu }$ with $\nu \cong 0.67$. Conventional Ginzburg-Landau formulas for critical fields and penetration depths, and mean-field predictions for fluctuation-enhanced quantities, must also be modified close to $T_c$.