Positron annihilation investigation of a Y1Ba2Cu3O7−δ epitaxial thin film

An enhanced signal-to-noise ratio, slow positron coincidence Doppler broadening technique has been applied to study the characteristics of a Y1Ba2Cu3O7−δ superconducting thin film at sample temperatures of 15 K and 290 K. In this investigation, a numerical analysis of the Doppler spectra was employed to the determine the shape parameter S, defined as the ratio between the number of counts in a central portion of the spectrum and the total number of counts in the entire spectrum. The S-parameter values near 0.56 were relatively constant while the positron energies increased, which indicated the presence of voids in the thin film. The S-parameter values for the Y1Ba2Cu3O7−δ thin film showed no temperature dependence at temperatures above or below Tc because the positron trapping rate in vacancy-type defects was mostly influenced. The effect of the S-parameters caused by open volume defects is believed to be greater than the effect of the S-parameters caused by the electronic state transition in the Y1Ba2Cu3O7−δ superconductor.