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Huth, M., Chiang, C.-T., Tr├╝tzschler, A., Schumann, F. O., Kirschner, J., Widdra, W.

Electron pair emission detected by time-of-flight spectrometers: Recent progress
Applied Physics Letters 104, (6),pp 061602/1-4 (2014)
We present results for electron coincidence spectroscopy using two time-of-flight (ToF) spectrometers. Excited by electron impact, the energy and momentum distribution of electron pairs emitted from the Cu(111) surface are resolved and a spectral feature related to the Shockley surface state is identified. By combining the two ToF spectrometers with a high-order harmonic generation light source, we demonstrate double photoemission spectroscopy in the laboratory that required synchrotron radiation in the past. Utilizing this setup, we report results for (c,2e) on NiO(001) on Ag(001) excited with light at 30 eV photon energy.