JETP Letters: issues online

There exist numerous experimental studies of the perpendicular and parallel upper critical magnetic fields in d-wave layered superconductors. They are usually theoretically fitted by the so-called Werthamer, Helfand, and Hohenberg (WHH) results, obtained for an isotropic 3D s-wave superconductors. As was theoretically shown by us and by Bulaevskii, layered compounds are characterized by different ratios of the parameter H_c2(0) / (| d H_c2 / d T|_{T_c} T_c) , where H_c2(0) is the upper critical magnetic field at T=0 and | d H_c2 / d T|_{T_c} is the so-called Ginzburg-Landau slope near T_c. In this paper, we show that for perpendicular upper critical magnetic field of a d-wave layered superconductor, the above discussed parameter is equal to $H_{c2}(0) / (| d H_{c2} / d T|_{T_c} T_c) \approx 0.629$ . To derive this result, we use exact method of the Green's functions formulation of the BCS microscopic theory of superconductivity by Gor'kov. We compare our results with experimental ones, obtained on the d-wave superconductor YBa₂Cu₃O_7-δ.