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Schumann, F. O., Winkler, C., Kirschner, J.

Correlation effects in two electron photoemission
Physical Review Letters 98, pp 257604/1-4 (2007)
Many-body effects in solids are ultimately related to the correlation among electrons, which can be probed by double photoelectron emission. We have investigated the electron pair emission from a Cu(111) surface upon photon absorption. We are able to observe for the first time the full extension and shape of a depletion zone around the fixed emission direction of one electron. It has an angular extension of  1.2 rad, which is independent of the electron energy.