  We apply ultrafast spectroscopy to establish a time-domain hierarchy between
structural and electronic effects in a strongly-correlated electron system. We
discuss the case of the model system VO2, a prototypical non-magnetic compound
that exhibits cell doubling, charge localization and a metal-insulator
transition below 340 K. We initiate the formation of the metallic phase by
prompt hole photo-doping into the valence band of the low-T insulator. The I-M
transition is however delayed with respect to hole injection, exhibiting a
bottleneck timescale that corresponds to half period of the phonon connecting
the two crystallographic phases. This experiment indicates that this
controversial insulator may have important band-like character.

Strongly Correlated Electrons