Critical nucleation in the phototransferred metastable phase of Cs2Au2Br6

We have investigated temporal evolution from the phototransferred metastable state to the ground state, i.e., from the single-valence (SV) to the mixed-valence (MV) states, in the perovskite-type gold complex Cs2Au2Br6. In this system, we can control the relative stability of the states via external pressure P. We have observed a sudden increase of the relative volume v(Mv) of the MV state against time, and have interpreted it in terms of the critical nucleation. The critical time t(c), where v(Mv) becomes 1/2, increases exponentially with P, reflecting the enhanced potential barrier for critical nucleation.