Influence of structural disorder on low-temperature behavior of penetration depth in electron-doped high-TC thin films

To probe the influence of structural disorder on low-temperature behavior of magnetic penetration depth, lambda(T), in electron-doped high-T-C superconductors, a comparative study of high-quality Pr1.85Ce0.15CuO4 (PCCO) and Sm1.85Ce0.15CuO4 (SCCO) thin films is presented. The lambda(T) profiles are extracted from conductance-voltage data using a highly-sensitive home-made mutual-inductance technique. The obtained results confirm a d-wave pairing mechanism in both samples (with nodal gap parameter Delta(0)/k(B)T(C) = 2.0 and 2.1 for PCCO and SCCO films, respectively), substantially modified by impurity scattering (which is more noticeable in less homogeneous SCCO films) at the lowest temperatures. More precisely, Delta lambda(T) = lambda(T) - lambda(0) is found to follow the Goldenfeld-Hirschfeld interpolation formulae Delta lambda(T)/lambda(0) = AT(2)/(T + T-0) with T-0 = ln(2)k(B)Gamma(1/2)Delta(1/2)(0) being the crossover temperature which demarcates pure and impure scattering processes (T-0/T-C = 0.13 and 0.26 for PCCO and SCCO films, respectively). The value of the extracted impurity scattering rate Gamma correlates with the quality of our samples and is found to be much higher in less homogeneous films with lower T-C. (c) 2006 Elsevier B.V. All rights reserved.