Positron-annihilation studies on the YBa2Cu4O8 superconductor

Positron-lifetime and Doppler-broadened annihilation-radiation line-shape parameter S in YBa2Cu4O8 are observed to decrease with temperature below Tc. The calculation of the positron-density distribution shows that the maximum of the positron density is in the region between the Cu-O double chains. The correlation between the temperature dependence of annihilation parameters and the positron-density distribution is discussed. The decrease in annihilation parameters below Tc is understood in terms of a local electron transfer from the CuO2 layers to the Cu-O chains in the superconducting state.