Kondo lattice effects and the collapse of lattice coherence in Yb1-xLuxB12 studied by hard x-ray photoelectron spectroscopy

Kondo semiconductor YbB12 and the Lu-substituted Yb1-xLuxB12 (x=1/8) alloy have been studied by the bulk-sensitive hard x-ray (h nu similar to 8 keV) photoelectron spectroscopy at temperatures from 200 down to 20 K. To check the Kondo lattice effects for the bulk electronic states, the temperature dependence of the bulk Yb valence and 4f peak positions in both systems is analyzed with use of the single-impurity Anderson model (SIAM) by considering the crystalline electric field effects. For x=0, the temperature dependence of the bulk electronic states cannot be interpreted within the SIAM, whereas those for x=1/8 could be understood by the SIAM predictions due to the collapse of the lattice coherence by the Lu substitution. These results indicate that the Kondo lattice effects are important for pure YbB12 and play essential roles for forming a narrow gap at low temperatures.