  The ultrafast response of the prototype Mott-Hubbard system (V1-xCrx)2O3 was
systematically studied with fs pump-probe reflectivity, allowing us to clearly
identify the effects of the metal-insulator transition on the transient
response. The isostructural nature of the phase transition in this material
made it possible to follow across the phase diagram the behaviour of the
detected coherent acoustic wave, whose average value and lifetime depend on the
thermodynamic phase and on the correlated electron density of states. It is
also shown how coherent lattice oscillations can play an important role in some
changes affecting the ultrafast electronic peak relaxation at the phase
transition, changes which should not be mistakenly attributed to genuine
electronic effects. These results clearly show that a thorough understanding of
the ultrafast response of the material over several tenths of ps is necessary
to correctly interpret its sub-ps excitation and relaxation regime, and appear
to be of general interest also for other strongly correlated materials.
