Ultrafast dynamics of reversible photoinduced phase transitions in rubidium manganese hexacyanoferrate investigated by midinfrared CN vibration spectroscopy

Photoinduced phase switching dynamics between LTP (low-temperature phase: Fe2+-CN-Mn3+) and PIHTP (photoinduced high-temperature phase: Fe3+-CN-Mn2+) in rubidium manganese hexacyanoferrate at 4 K was investigated by visible pump midinfrared probe transient absorption spectroscopy. By monitoring the CN stretching vibration modes, which are sensitive to the valence states of the adjacent metal ions, we could qualify not only LTP and PIHTP but also the phase boundary configurations (Fe2+-CN-Mn2+ and Fe3+-CN-Mn3+). In addition, by irradiating with another light inducing the reverse process to the pump light, we were able to apply a pump-probe measurement to the persistent phase transitions. The electronic and structural dynamics in the picosecond region were understood with a phenomenological spectral fitting model. In particular, in both directions of these phase transitions, the instantaneous generation of the boundary configuration was observed. This observation suggests that relatively small domains and/or low-dimensional fjord-like domains are created at the early stage of the transition.