Slow Dynamics of the Photoinduced Phase Transition in $Pd(dmit)_2$ Salts (dmit = 1,3-dithiol-2-thione-4,5-dithiolate)

Slow dynamics of the initially photoinduced state has been observed by the pump-probe type time-resolved reflection spectroscopy in the charge separated phase of the half-filled strong dimer system, $Et_2Me_2Sb[Pd(dmit)_2]_2$ (dmit = 1,3-dithiol-2-thione-4,5-dithiolate). We have succeeded to reproduce the probe photon energy dependence of the time profile qualitatively in the time delay range from 10 ps to 1 ns assuming the dynamical expansion of the domain of the photo-induced dimer-Mott insulating phase in the host charge-separated one.