Temperature dependence of upper critical fields and coherence lengths for optimally-doped YBa2Cu3O7–δ thin films

We report the comprehensive comparative analysis of the upper critical magnetic fields μHc2(0) obtained within Ginzburg–Landau (GL) and Werthamer–Helfand–Hohenberg (WHH) theories for optimally-doped YBa2Cu3O7–δ thin films. For different orientations of the magnetic field, our calculations give 638 and 153 T for μHc2(0), H || ab and μHc2(0), H || c, respectively, when using Hc2(0). For the first time, the temperature dependences of coherence lengths ξab(T) and ξc(T) within proposed theories were determined using 50 and 90% criteria of the normal state resistivity value ρN. The GL (0.9ρN) approach gives ξab(0) = 11.8 Å and ξc(0) = 3.0 Å which are in a good agreement with literature data. The implications of very short coherence lengths in HTSCs are discussed.