ELECTRON-POSITRON MOMENTUM DENSITY DISTRIBUTION IN DIAMOND

We have measured the momentum distribution of the electron-positron an nihilating pair in diamond as a function of crystallographic orientati on, using the Doppler broadening technique of positron annihilation sp ectroscopy. A 1% variation in the longitudinal projection of the momen tum distribution was observed as the sample was rotated about the [110 ] axis. This anisotropic distribution shows an excellent agreement wit h a theoretical calculation performed based on two component density f unctional theory in the local density approximation. The results sugge st strongly that the bulk positron density, though delocalized and inh omogeneous, has sufficient amplitude at the intra-bond regions such th at the annihilation characteristics are dominated by the bond electron density and momentum distribution.