Phonon-induced disorder in dynamics of optically pumped metals from nonlinear electron-phonon coupling

The nonequilibrium dynamics of matter excited by light may produce electronic phases that do not exist in equilibrium, such as laser-induced high-T_c superconductivity. Here we simulate the dynamics of a metal driven at initial time by a spatially uniform pump that excites dipole-active vibrational modes which couple quadratically to electrons. We study the evolution of electronic and vibrational observables and their coherences.  We provide evidence for enhancement of local electronic correlations, including double occupancy, accompanied by rapid loss of spatial structure, which we interpret as a signature of emergent effective disorder in the dynamics.  This effective disorder, which arises in absence of quenched randomness, dominates the electronic dynamics as the system evolves towards a correlated electron-phonon long-time state, possibly explaining why transient superconductivity is not observed. The pumped electron-phonon systems studied here, which are governed by nonlinear coupling, exhibit a much more substantial dynamical response than linearly coupled models relevant in equilibrium, thus presenting a pathway to new modalities for out-of-equilibrium phases. Our results provide a basis within which to understand correlation dynamics in pump-probe experiments.