Dp. Moore et al., Bulk electronic structure of YbInCu4 from photoemission: A unique test of the single impurity model, PHYS REV B, 62(24), 2000, pp. 16492-16499
The heavy fermion compound YbInCu4 presents a unique opportunity to test th
e single impurity model (SIM) owing to its isostructural phase transition a
t 42 K, whereby the Kondo temperature suddenly increases from 30 K above, t
o 400 K below the transition. Photoelectron spectroscopy (PES) at varying t
emperatures is well suited for this test, Previous researchers have claimed
that PES probes only a subsurface region which differs from the bulk, thus
rendering PES less than optimum for such a test. We present PES data in wh
ich a single-crystal sample was cooled through the phase transition only on
ce in order to minimize defect formation. We find clear evidence of the bul
k transition and no evidence for a subsurface region. The PES spectra do no
t agree with the predictions of the SIM and its approximate solution, the n
oncrossing approximation. We propose that only a periodic model is applicab
le to highly correlated, stoichiometric heavy fermion systems.