Nonequilibrium dynamics of suppression, revival, and loss of charge order in a laser-pumped electron-phonon system

An electron-phonon system at commensurate filling often displays charge order (CO) in the ground state. Such a system subject to a laser pulse shows a wide variety of behavior. A weak pulse sets up low-amplitude oscillations in the order parameter, with slow decay to a slightly suppressed value. A strong pulse leads to destruction of the charge order with the order parameter showing rapid, oscillatory, decay to zero. The regime in-between, separating the weak pulse CO sustained state from the strong pulse CO destroyed state, shows an initial rapid decay of the order parameter, followed by a low-amplitude quiescent state, and the rise to a finite steady-state value over a timescale τcr. The steady-state value goes to zero and τcr diverges as the pulse amplitude is increased towards a critical strength. We provide a complete characterization of the dynamics in this nonequilibrium problem for varying electron-phonon coupling and pulse strength, highlight the multiple gap-closing and -opening transitions that occur, and suggest a simple dynamical model incorporating the pulse-induced nonequilibrium electron population.