Photoemission from YbInCu4: testing the single impurity model

The electronic properties of single crystal YbInCu4 and YbAgCu4 have been i nvestigated by means of high resolution photoelectron spectroscopy. A first order, isostructural phase transition for YbInCu4 at 42K leads to changes in the Kondo temperature, of more than an order of magnitude. This phase tr ansition and accompanying Kondo temperature change provide the most direct test of the single impurity model to date. The photoemission results are in congruous with the single impurity model predictions for temperature depend ence, binding energy and 4f occupancy, encouraging a re-evaluation of the s ingle impurity model applicability.