The 2-dimensional angular correlation of positron annihilation distribution for singly-negative di-vacancies was studied experimentally and theoretically. An anisotropy of the distribution was detected in specimens with aligned di-vacancies, and could be reproduced by first-principles calculations that were based upon 2-component density functional theory. The calculations demonstrated that the anisotropy reflected the characteristic distribution of electrons around di-vacancies. It was concluded that the present method would be effective in providing microscopic information on vacancy-type defects.

Z.Tang, M.Hasegawa, T.Chiba, M.Saito, A.Kawasuso, Z.Q.Li, R.T.Fu, T.Akahane, Y.Kawazoe, S.Yamaguchi: Physical Review Letters, 1997, 78[11], 2236-9