Electron and hole polaron asymmetry in a two-band Peierls-Hubbard material

A combined experimental and theoretical analysis of the quasi-one-dimensional mixed-valence insulator [Pt(en${)}_2$][Pt(en${)}_2$ ${\mathrm{Cl}}_2$]⋅(${\mathrm{ClO}}_4$ ${)}_4$ (en=${\mathrm{N}}_2$ ${\mathrm{C}}_2$ ${\mathrm{H}}_8$) is given. Three intragap absorptions, observed directly by near- and mid-infrared single-crystal transmission experiments and indirectly by resonance-Raman excitation profiles, can be quantitatively accounted for with an extended Peierls-Hubbard chain model incorporating 3/4-filling of two bands, with striking asymmetry between electron and hole polarons. Analogies are drawn to modeling other strong-correlation novel materials, including oxide superconductors.