  FeSe$_{x}$Te$_{1-x}$ compounds present a complex phase diagram, ranging from
the nematicity of FeSe to the $(\pi, \pi)$ magnetism of FeTe. We focus on
FeSe$_{0.4}$Te$_{0.6}$, where the nematic ordering is absent at equilibrium. We
use a time-resolved approach based on femtosecond light pulses to study the
dynamics following photoexcitation in this system. The use of
polarization-dependent time- and angle-resolved photoelectron spectroscopy
allows us to reveal a photoinduced nematic metastable state, whose
stabilization cannot be interpreted in terms of an effective photodoping. We
argue that the 1.55 eV photon-energy-pump-pulse perturbs the $C_4$ symmetry of
the system triggering the realization of the nematic state. The possibility to
induce nematicity using an ultra-short pulse sheds a new light on the driving
force behind the nematic symmetry breaking in iron-based superconductors. Our
results weaken the idea that a low-energy coupling with fluctuations is a
necessary condition to stabilize the nematic order and ascribe the origin of
the nematic order in iron-based superconductors to a clear tendency of those
systems towards orbital differentiation due to strong electronic correlations
induced by the Hund's coupling.
