Role of quantum fluctuations in the temperature dependence of intragap absorption in an MX chain complex

We study the temperature dependence of persistent near-infrared absorption bands induced in single crystals of [Pt(en${)}_2$][Pt(en${)}_2$${\mathrm{Cl}}_2$](${\mathrm{ClO}}_4$${)}_4$, where en=ethylenediamine, by irradiation with 488-nm light. If the temperature is changed between 10 and 200 K in dark after irradiation, these bands show significant changes in the spectral position, line shape, and intensity. The behaviors of the mean energy and second and third moments of the A band are interpreted consistently in terms of a quantum-fluctuation model of solitons bound by shallow, periodic potential wells.