Kondo lattice effects of YbAl3 suggested by temperature dependence of high-accuracy high-energy photoelectron spectroscopy

By use of high-resolution soft X-rays, intrinsic temperature dependences of bulk Yb 4f photoelectron spectra were obtained for fractured surfaces of high-purity YbAl3 single crystals. The spectra of not only bulk 4f(13) but also 4f(12) final states are analyzed by noncrossing approximation (NCA) calculation for the f(14), f(13), and f(12) initial states based on the single impurity Anderson model (SIAM). In order to consistently interpret the temperature dependences of both 4f(13) and 4f(12) final states, however, it is found that a constant set of parameters of the hybridization strength Delta, bare 4f energy epsilon(f) and electron correlation energy U-ff is insufficient. The limitation of SIAM is confirmed for YbAl3 and the importance of the Kondo lattice effects is suggested.