Cuprate interband model and doping dependence of the coherence length
The free energy expansion of a two-band pair-transfer superconductor is developed. A critical in temperature and a noncritical coherence length appear. The effective in-planeab, H c c2 ∼ � −2 ab and the thermodynamic critical magnetic field (Hc0) on the whole hole doping (p) scale are calculated for a "typical" cuprate. A doping- prepared bare spectrum with normal state gaps quenched by doping has been used. The coherence lengthab falls with p first rapidly. A moderate enhancement starts when the "cold" defect band overlap with the valence band is reached. At overdoping �ab rises markedly. The H c2 curve shows a maximum before Tcmax. The bell-like Hc0-curve follows closely Tc, superconducting gaps, and superfluid density. The theoreticalab(p) nonmonotonic curve on the whole doping scale agrees with a recent experimental finding. PACS: 74.20.-z; 74.72.-h