Jj. Joyce et al., PHOTOEMISSION AND THE ELECTRONIC-PROPERTIES OF HEAVY FERMIONS - LIMITATIONS OF THE KONDO MODEL, Physica. B, Condensed matter, 205(3-4), 1995, pp. 365-370
The electronic properties of Yb-based heavy fermions have been investi
gated by means of high resolution synchrotron radiation photoemission
and compared with predictions of the Kondo model. The Yb heavy fermion
photoemission spectra show significant disagreement with the Kondo mo
del predictions (as calculated within the Gunnarsson-Schonhammer compu
tational method). Moreover, the Yb heavy fermion photoemission spectra
give strong indications of core-like characteristics and compare favo
rably to purely divalent Yb metal and core-like Lu 4f levels. The heav
y fermions YbCu2Si2, YbAgCu4 and YbAl3 were measured and shown to have
lineshapes much broader and deeper in binding energy than predicted b
y the Kondo model. The lineshape of the bulk component of the 4f emiss
ion for these three heavy fermion materials was compared with that fro
m Yb metal and the Lu 4f levels in LuAl3. The heavy fermion materials
show no substantive spectroscopic differences from 4f levels observed
in Yb metal and LuAl3. Also, the variation with temperature of the 4f
lineshape was measured for Yb metal and clearly demonstrates that phon
on broadening plays a major role in 4f level lineshape analysis and mu
st be accounted for before considerations of correlated electron reson
ance effects are presumed to be at work.