  Technology moves towards ever faster switching between different electronic
and magnetic states of matter. Manipulating properties at terahertz rates
requires accessing the intrinsic timescales of electrons (femtoseconds) and
associated phonons (10s of femtoseconds to few picoseconds), which is possible
with short-pulse photoexcitation. Yet, in many Mott insulators, the electronic
transition is accompanied by the nucleation and growth of percolating domains
of the changed lattice structure, leading to empirical time scales dominated by
slow coarsening dynamics. Here, we use time-resolved X-ray diffraction and
reflectivity measurements to investigate the photoinduced insulator-to-metal
transition in an epitaxially strained thin film Mott insulator Ca2RuO4. The
dynamical transition occurs without observable domain formation and coarsening
effects, allowing the study of the intrinsic electronic and lattice dynamics.
Above a fluence threshold, the initial electronic excitation drives a fast
lattice rearrangement, followed by a slower electronic evolution into a
metastable non-equilibrium state. Microscopic calculations based on
time-dependent dynamical mean-field theory and semiclassical lattice dynamics
within a recently published equilibrium energy landscape picture explain the
threshold-behavior and elucidate the delayed onset of the electronic phase
transition in terms of kinematic constraints on recombination. Analysis of
satellite scattering peaks indicates the persistence of a strain-induced
nano-texture in the photoexcited film. This work highlights the importance of
combined electronic and structural studies to unravel the physics of dynamic
transitions and elucidates the role of strain in tuning the timescales of
photoinduced processes.
