POSITRON ANNIHILATION STUDY ON SUPERCONDUCTING SINGLE CRYSTAL BSCCO

Ⅰ. INTRODUCTIONPositron annihilation spectroscopy (PAS)is a sensitive probe for investigation of the electronic structure, the defects and phase transition of solids. For conventional superconductors, the BCS theory predicts a redistribution of occupied states in k space due to the formation of Cooper pairs. The formation of Cooper pair leads to a smearing of the Fermi surface. Early theories suggested that one should observe an increase in positron