Theoretical Approach For Elastically Driven Cooperative Switching Of Spin-Crossover Compounds Impacted By An Ultrashort Laser Pulse

In this paper, we use an elastic model in order to study the elastically driven cooperative switching of spin-crossover materials after femtosecond laser excitation. In this model, the molecules occupy a triangular lattice in open-boundary systems, and they are connected by springs. The volume change of a molecule between its two possible spin states, low-spin and high-spin, determines a variation of the spring length and therefore modifies elastic interactions between molecules, which propagates throughout the whole sample as elastic distortions. This model is able to reproduce the multistep out-of-equilibrium response to ultrashort laser excitation and especially the elastically driven cooperative response. It is developed in order to predict the behavior of the system as a function of its different physical parameters, such as the magnitude of the elastic constant or the homogeneity of the photoexcitation. The contribution of the reorganization of the molecular states during elastic steps, leading to clusters of high-spin molecules toward the edge or the corners, is also revealed.