Angle-resolved pair photoemission theory for correlated electrons

In this paper, we consider the possibility and conditions for pair photoemission, whereby two incident photons emit pairs of electrons from a candidate material, as a method to measure and visualize electronic correlations. As opposed to double photoemission-where a single photon precipitates the ejection of a pair of electrons via a subsequent electron energy loss scattering process-we show that pair photoemission need not be limited to interference between initial photoelectrons and valence electrons and moreover can occur without the energy penalty of two work functions. This enables detection of pairs of electrons at high-energy resolution that may be correlated in the same quantum many-body states.