Excess Conductivity Analysis and the Critical Region in Be-Doped Cu0.5Tl0.5Ba2Ca1−y Be y Cu0.5Zn1.5O8−δ Superconductors

Abstract

The excess conductivity analysis of as-prepared and oxygen-annealed Be-doped Cu0.5Tl0.5Ba2Ca1−yBey(Cu0.5Zn1.5)O8−δ (y=0, 0.15, 0.3, 0.45) superconducting samples is carried out in the critical regimes and beyond. Various superconducting parameters, like the zero resistance critical temperature Tc, mean field critical temperature \(T_{c}^{mf}\), onset temperature of superconductivity T∗, the crossover temperature TG of the critical and 3D fluctuations and dimensionality of fluctuations are determined. From the 3D to 2D crossover, and at the termination of 2D fluctuations, the coherence length ξc(0) along the c-axis, the coupling constant J, the phase relaxation time τφ, the Fermi velocity VF of the carriers and Fermi energy EF are calculated. Using the Ginzburg–Landau (G–L) equations in the critical regime, the thermodynamic critical magnetic field Bc(0), the lower critical field Bc1(0), the upper critical field Bc2(0) and the critical current density Jc(0) are also calculated from these analyses. Four fluctuation regions above Tc are observed for all of the samples, namely the critical (cr), three-dimensional (3D), two-dimensional (2D) and zero-dimensional (0D) fluctuations regions. It is observed that with the increased Be content at Ca sites, ξc(0), VF and the coupling constant J are increased, which shows that the inter-planar coupling is improved by the incorporation of Be atoms at the Ca sites.