Enhanced coherence length and interplane coupling by Ti doping in (Cu, Tl)-1223 superconductors: Para conductivity analyses

Abstract

The fluctuation induced conductivity (FIC) analyses of Ti doped (Cu0.5Tl0.5)Ba2(Ca2-xTix)Cu3O10-δ superconducting samples have been carried. Aslamazov-Larkin (AL) and Lawrance-Doniach (LD) models were used to study the FIC in the critical, 3D, 2D and 0D regions. Maki-Thompson (MT) model has been employed to study the effect of the Cooper-pairs on the normal electrons. From these analyses the coherence length along the c-axis, ξc (0), the inter-plane coupling constant, J, the phase relaxation time, τφ , Fermi velocity, VF, and the energy essential for breaking apart the Cooper's pairs, E, are determined. From the cross-over temperature, TG, of critical to 3D regime the Ginsberg number, NG, has been calculated. Using NG and the Ginsburg–Landau (GL) equations, various important parameters like thermodynamic critical magnetic field, Bc(0), the lower critical field, Bc1(0), the upper critical field, Bc2(0), the critical current density, Jc (0), as well as the penetration depth, λp.d, have been calculated. Values of Tc, TG, Tcmf, ξc(0) and J are increased with the increasing Ti contents. All the fluctuation regimes have been shifted to higher temperature and the anisotropy is reduced with the doping of Ti. Also VF and E are found to enhance with Ti doping while the phase relaxation time is reduced. The most probable reason for all these improved parameters is the smaller ionic radius of Ti atom, which brings the CuO2 planes closer together thereby enhancing the density of Cooper pairs in the unit cell. The values of Bc(0), Bc1(0), and Jc(0) are suppressed while the values of λp.d and κ are increased with increased Ti contents. The suppression in the critical fields and current density may be attributed to the decrease in the free energy difference of the normal and superconducting states.