Direct and core-resonant double photoemission from Cu(001)

Abstract

We have measured the correlated electron pair emission from a Cu(001) surface by bothdirect and core-resonant channels upon excitation with linearly polarized photons of energyfar above the 3p threshold. As expected for a single-step process mediated by electroncorrelation in the initial and final states, the two electrons emitted by the direct channelcontinuously share the sum of the energy available to them. The core-resonant channel isoften considered in terms of successive and independent steps of photoexcitation and Augerdecay. However, electron pairs emitted by the core-resonant channel also share theirenergy continuously to jointly conserve the energy of the complete process. Bydetecting the electron pairs in parallel over a wide range of energy, evidence of thecore-resonant double photoemission proceeding by a coherent single-step process is moststrikingly manifested by a continuum of correlated electron pairs with a sum energycharacteristic of the process but for which the individual electrons have arbitrary energiesand cannot meaningfully be distinguished as a photoelectron or Auger electron.