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

Band-resolved double photoemission spectroscopy on correlated valence electron pairs in metals
Physical Review Letters 118, (13),pp 136401/1-5 (2017)
Correlated valence electrons in Ag and Cu are investigated using double photoemission spectroscopy driven by a high-order harmonic light source. Electron pairs consisting of two d electrons as well as pairs with one sp and one d electron are resolved in the two-dimensional energy spectrum. Surprisingly, the intensity ratio of sp-d to d-d pairs from Ag is 3 times higher than in the self-convoluted density of states. Our results directly show the band-resolved configurations of electron pairs in solids and emphasize a band-dependent picture for electron correlation even in these paradigmatic metals.