Electronic structure and positron annihilation in B2-ordered CuZn

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Abstract
The momentum density of annihilation pairs (MDAP) in B2-ordered stoichimetric CuZn alloy is determined ab initio on the basis of an APW band-structure calculation. The effect of the electron-positron interaction is considered by means of an energy-dependent Kahana-like enhancement factor. A direct comparison of calculated and experimental positron annihilation angular correlation curves is performed, taking into account the angular resolution of the measuring device and the thermal motion of the positron. As in iron alloys, it is found that the enhancement of the contribution of d electrons to the MDAP is appreciably lower than that of the contribution of sp electrons belonging to the conduction band. A simple model explaining semiquantitatively the different enhancement factors for both groups of electrons is proposed.