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.
@article{arxiv.cond-mat/0403214,
title = {Evidence for a Structurally-driven Insulator-to-metal Transition in VO2: a View from the Ultrafast Timescale},
author = {A. Cavalleri and Th. Dekorsy and H. H. Chong and J. C. Kieffer and R. W. Schoenlein},
journal= {arXiv preprint arXiv:cond-mat/0403214},
year = {2007}
}