  We combine ultrafast electron diffraction and time-resolved terahertz
spectroscopy measurements to unravel the connection between structure and
electronic transport properties during the photoinduced insulator-metal
transitions in vanadium dioxide. We determine the structure of the metastable
monoclinic metal phase, which exhibits anti-ferroelectric charge order arising
from a thermally activated, orbital-selective phase transition in the electron
system. The relative contribution of this photoinduced monoclinic metal (which
has no equilibrium analog) and the photoinduced rutile metal (known from the
equilibrium phase diagram) to the time and pump-fluence dependent multi-phase
character of the film is established, as is the respective impact of these two
distinct phase transitions on the observed changes in terahertz conductivity.
Our results represent an important new example of how light can control the
properties of strongly correlated materials and elucidate that multi-modal
experiements are essential when seeking a detailed connection between ultrafast
changes in optical-electronic properties and lattice structure in complex
materials.
