Temperature dependence of the Kondo peak in photoemission spectra of YbAgCu

Temperature dependent photoelectron spectra of the heavy fermion YbAgCu show that the Kondo resonance is strongly depressed with increasing temperature. The observed reduction is fully consistent with the predictions of the Anderson impurity model, and reveals the transition from a Fermi liquid at low temperature to localized moments above the characteristic Kondo temperature. Despite this important experimental confirmation of the model, discrepancies exist between the experimental and calculated linewidth of the resonance. It is argued that a more realistic treatment of the photoemission process would improve the agreement between theory and experiment. © 1993 Springer-Verlag.