Dynamical Phase Transition in a Spin–Crossover Complex

Abstract

Density n HS of photoexcited high-spin (HS) sites in a spin–crossover film (Nafion-[Fe(Htrz) 3 ]; Htrz = 1,2,4-4H-triazole) was systematically investigated against temperature T and excitation power density P . At low temperatures (≤35 K), the n HS – P curve shows a nonlinear increase when P reaches a critical value ( P c ). We interpreted the increase in terms of the dynamical phase transition into the condensed state of photoexcited HS molecules, and derived the P – T phase diagram. The P – T phase diagram and the n HS – P curves were analyzed with an Ising-like model which includes a temperature-dependent field.