  We investigate the properties of the spectral function A(omega,U) of
correlated electrons within the Hubbard model and dynamical mean-field theory.
Curves of A(omega,U) vs. omega for different values of the interaction U are
found to intersect near the band-edges of the non-interacting system. For a
wide range of U the crossing points are located within a sharply confined
region. The precise location of these 'isosbestic points' depends on details of
the non-interacting band structure. Isosbestic points of dynamic quantities
therefore provide valuable insights into microscopic energy scales of
correlated systems.
