In core-level photoemission spectra of simple metals, distinct plasmon loss peaks appear due to excitation of plasma oscillations. This process can be classified into intrinsic and extrinsic ones. Here, plasmon excitation processes by the core-hole potential are called intrinsic and inelastic plasmon losses during photoelectron transport to the surface are called extrinsic. Although there have been many attempts to distinguish these two processes in photoemission spectra, some controversies still remain. Moreover there can be quantum mechanical interference between these two processes. This interference effect has been often neglected in the analyses of experimental data. In this research, we performed angle-resolved Al 2p core-level photoemission experiments and analyzed plasmon loss peak intensity at relatively low photoelectron kinetic energy. Consequently, we found characteristic behavior of plasmon loss peaks as a function of the angle between the polarization vector of incident photons and photoemission direction. We also performed full-quantum-mechanical calculation taking into account the interference, which satisfactorily predicted the experimental results.
