Coherence lengths and magnetic penetration depths in YBa₂Cu₃O₇ and YBa₂Cu₄O₈ superconductors

Abstract

The superconducting state parameters of the high-T _c layered structure YBa₂Cu₃O₇ (Y123) and YBa₂Cu₄O₈ (Y124) systems have been evaluated. The two-dimensional (2D) CuO₂ planes as well as one-dimensional (1D) CuO chains are the important features of these systems. The anisotropy of the layered structure is well reflected in the shape of open Fermi surface. The carrier effective mass (m ^*) and the charge carrier density (n _v) are deduced from the Fermi velocity and the Hall effect coefficient, respectively, following the electronic energy band structure studies (EEBS) within the local approximation to the density functional theory. Then the anisotropic magnetic penetration depth (λ_L) as well as the coherence length (ξ) are estimated. The analysis yields smaller values of (λ_L) than those revealed from penetration depth measurements in Y124 while the (λ_L) values appear higher in Y123 when compared with the muon spin relaxation (μSR) and radio frequency surface impedance (RSI) measurements. The deduced values of coherence lengths and its anisotropy are consistent with the reported data. The temperature dependence of the in-plane magnetic penetration depth and the Ginzburg-Landau parameter predicts that they are of a similar nature as those revealed from experiments. The results on lower and upper critical magnetic fields are also presented. It is found, with a simple analysis of the superconducting state, that the parameters of YBCO (124 and 123) based on EEBS are consistent but are not in good agreement with experiments. Furthermore, the transport parameters (m ^*,n _v) as obtained from the Fermi Liquid description are used to determine the in-plane magnetic properties. This technique permits a reasonably good agreement with recently published data. The implications of the above analysis are discussed.