Threshold phenomena under photoexcitation of spin-crossover materials with cooperativity due to elastic interactions

Photo-induced switching from the low-spin state to the high-spin state is studied in a model spin-crossover material with long-range interactions induced by elastic distortions due to different molecular sizes of the two spin states. At a threshold value of the light intensity, nonequilibrium critical behavior is observed in the form of a jump in the high-spin fraction, corresponding to a mean-field spinodal point. Finite-size scaling of the divergence of the transition time is revealed through kinetic Monte Carlo simulations.