Superconductivity in Zn-doped tetragonal LaBaCaCu₃O_7-δ systems

Abstract

Resistivity and ac susceptibility of Zn-doped samples of the LaBaCaCu₃O_7−δ (LBCCO) system have been measured for Zn content of 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, and 3.0% at. wt. X-ray diffraction has been used to find the lattice parameters of the samples. The samples remain tetragonal for all the considered concentrations of Zn. Idometry and thermogravimetric analyses have been done to estimate the oxygen content of different samples. Analyzing the resistivity and ac susceptibility data, the following conclusions are drawn about the role of Zn in the LBCCO samples. (1) The conduction mechanism of electrons appears to follow a crossover from the purely metallic regime to the localization regime due to either weak localization or electron-electron interaction effects after about 1.5% Zn. (2) The superconducting transition as revealed by the resistivity vs temperature curves or susceptibility vs temperature curves becomes sharper with Zn increasing content of Zn up to 1.0%. After 1.5% the resistive and ac susceptibility transitions become broader with increasing Zn. (3) T_c depression up to Zn content of 1.0% seems due to direct suppression of the effective pairing interaction, while at and above 2.5% Zn T_c depression is expected to be due to disorder effects such as reduction of density of states at the Fermi energy.