Evolution of electronic states in the Kondo alloy systemYb1−xLuxB12

We have studied the effect of Lu substitution on the Kondo insulator YbB 12 by high-resolution photoemission. Comparison of the spectra of YbB 12 ,Y b 0.5Lu 0.5B 12 , and LuB 12 reveals that the density of states ~DOS! of the B sp -derived conduction band near the Fermi level is reduced in YbB 12 over a rather wide (; 40 meV! energy region. Lu substitution ~i! recovers the reduced B sp DOS, ~ii! shifts the Yb 4 f -derived Kondo peak towards higher binding energy, and ~iii! decreases the Yb valence. These results are consistently analyzed using the Anderson-impurity model, and imply interaction between the Yb 4 f ions mediated by the Yb 4 f -B sp hybridization in YbB 12 . @S0163-1829~97!03846-0#