Point-geometry angular correlation curves for Cu: A study of enhancement in positron annihilation

Abstract

New band-structure calculations of point-slit angular correlation curves for positron annihilation in Cu single crystals are compared with measurements by Mader and Berko et al. Corrections are applied for the geometrical resolution and for enhancement due to ${e}^{\ensuremath{-}}\ensuremath{-}{e}^{\ensuremath{-}}$ and ${e}^{+}\ensuremath{-}{e}^{\ensuremath{-}}$ correlations. A new energy-dependent form of "Kahana enhancement" is proposed that gives excellent agreement between theory and experiment if the core contribution is reduced by a factor of 5. The results qualitatively confirm the enhancement of umklapp contributions derived by Hede and Carbotte. No indication is found for a de-enhancement of the umklapp components proposed by Fujiwara et al. Calculated curves for $\ensuremath{\alpha}$-${\mathrm{Cu}}_{0.7}$${\mathrm{Zn}}_{0.3}$ obtained on the basis of a rigid-band model are given for future reference.