Photoinduced infrared absorption of quasi-one-dimensional halogen-bridged binuclear transition-metal complexes

We investigate the optical conductivity of photogenerated solitons in quasi-one-dimensional halogen-bridged binuclear transition-metal (MMX) complexes with particular emphasis on a comparison among the three distinct groups: A4[Pt2(P2O5H2)4X]·nH2O (X=Cl, Br, I; A=Na, K, NH4,…), Pt2(RCS2)4I (R=CnH2n+1,) and Ni2(CH3CS2)4I which exhibit a mixed-valent ground state with the X sublattice dimerized, that with the M2 sublattice dimerized and a Mott-Hubbard magnetic ground state, respectively. Soliton-induced absorption spectra for A4[Pt2(P2O5H2)4X]·nH2O should split into two bands, while that for Pt2(RCS2)4I and Ni2(CH3CS2)4I should consist of a single band. The excitonic effect is significant in Ni2(CH3CS2)4I.