Pavlyukh Y., Schüler M., Berakdar J.

This work provides a unified theoretical treatment of the single- and correlated double-electron emission from a general electronic system. Using Feshbach projection method, the states of interest are selected by the projection operator; the Feshbach-Schur map determines the effective Hamiltonian and the optical potential for the emitted electrons. On the other hand, the nonequilibrium Green?s functions method is demonstrated to be a complementary approach, and an explicit correspondence between both methods is established. For a self-contained exposition, some results on single-electron emission are rederived using both formalisms. New insights and results are obtained for the correlated electron-pair emission: This includes the effective two-electron Hamiltonian, the explicit form of the Feshbach self-energy in terms of the many-body self-energies, and the diagrammatic expansion of the two-particle current. As an illustration of the diagrammatic technique, the process of the two-particle emission assisted by the excitation of plasmons is explicitly worked out.

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