  Kondo effect is an example of asymptotic freedom where the antiferromagnetic
coupling between a localized magnetic moment and valence electrons, increases
with reducing temperature. The electronic spectral function for such a system
predicts a narrow Kondo resonance close to Fermi energy below its Kondo
temperature 'TK'. The internal energy level structure of the localized magnetic
moment introduces sidebands near the Kondo resonance, each with its respective
Kondo temperature increasing as the sideband position moves towards higher
binding energies. Consequently, the temperature dependence of the resonance
features becomes weaker as we go towards higher binding energies. Here, we show
a Ce4f photoemission spectral evolution obtained from a prototypical Kondo
system CeAl2, departing from the predictions of the spectral function. Our
measurements reveal a uniform temperature dependence for all the well screened
Ce4f photoemission features (4f1 final state), which are usually interpreted as
resonance features, as we reduce the temperature suggesting that the resonance
interpretation for the 4f1 final state features is not appropriate. Instead,
the spectral evolution is explained simply by the temperature dependence of the
strength of the coupling between Ce4f and valence electrons, which remains
uniform over the range of 4f1 final state features. As a possible explanation
to the observed spectral evolution, we propose the phenomenon of collapse of
the Kondo singlet wave function upon photoelectron kinetic energy measurement,
analogous to the wave function collapse observed upon measurements performed on
an entangled EPR (Einstein, Podolsky, Rosen) pair. Our proposal highlights how
experiments studying single particle properties, when performed on a quantum
system, give incomplete information about the many-body physics of the system.
