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Rydberg-like surface states are identified at Au (100) and Cu (100) surfaces by use of inverse photoemission with tunable photon energy. The binding energy (0. 6 eV below vacuum) and width (0. 3 eV full width at half maximum) of the n=1 state agree well with previous calculations. Theory yields the expectation that these states represent a widespread phenomenon at surfaces.
Straub et al. (Mon,) studied this question.