Angular correlation distribution of electron-positron annihilation in graphite

Abstract

Using the empirical pseudopotential method for the electron wavefunction and the variational positron wavefunction, the authors have calculated the one- and two-dimensional angular correlation distribution of electron-positron annihilation (ACAR) as well as the electron momentum distribution (EMD) for graphite. The calculated ACAR as well as its anisotropy are in good agreement with experiments. Due to the presence of the positron, the calculated ACAR shows stronger anisotropy than the corresponding EMD, which is in agreement with the experimental data. It is shown that the layer structure of graphite is more clearly exhibited by the ACAR than the EMD. The remaining discrepancy between the presently calculated ACAR distribution and the experimental spectra is discussed and it is argued that it originates from the quality of the single-crystal sample used in the experiments and the electron-positron many-body interaction which has not been included in their theoretical treatment.