In-plane Mg doping in YBa₂Cu₃O₇: influence on the superconducting anisotropy

Abstract

Melt textured single domains of Mg-doped YBa2Cu3O7 superconductors with homogeneous cation distribution and narrow superconducting transitions have been prepared by top seeding growth. The strong reduction in the transition temperature, Tc, found in Mg substituted YBa2(Cu1-xMgx)3O7 samples, suggests that Mg ions occupy the CuO2 planes. For low doping concentrations, the decrease in Tc is estimated as dTc/dx≈-12 K/at% Mg. Instead, for high doping values, a saturation of Mg substitution occurs within the matrix, leading to MgO segregation. The maximum amount of Mg atomic substitution has been estimated as x≈4 at%, shifting Tc down to Tc≈45 K. Studies of anisotropy of the superconducting state from magnetoresistance measurements reveal that, concomitant to the decrease in Tc, the mass anisotropy decreases with Mg doping. These results are interpreted in the framework of non-magnetic impurity scattering effects in d-wave superconductors, where the main distinguishing feature has been the development of new quasi-particle states within the superconducting gap.