Excess conductivity and magneto-conductivity studies in pure and Ag-doped (La_(1-x)Y_x)_2Ba_2CaCu_5O_z superconductors

摘要

The temperature variations of electrical resistivity have been measured on pure and 5 wt percent Ag-doped (La_(1-x)Y_x)_2Ba_2CaCu_5O_z superconductors in the absence and presence of 1 T magnetic field. The electrical resistivity data in the absence of magnetic field were analysed in terms of fluctuation-induced excess conductivity in the mean-field regime by using the Aslamazov-Larkin (AL), Lawrence-Doniach (LD) and Maki-Thompson (MT) models. The fluctuations in the amplitude of order parameter are found to be two dimensional in nature. The magneto-resistivity data were analysed in terms of fluctuation magneto-conductivity by using the AL and MT models for layered superconductors and by taking into account both orbital and Zeeman terms. These materials exhibit a strong pair breaking effect and the typical phase breaking time at 100 K is found to be of the order of 10~(-16) s. The typical values of coherence lengths along the ab-plane and along the c-direction at 0 K are found to be 28.5 and 0.4 A.