Spin-Orbital Pattern Dependent Polaron Absorption in Manganites

We systematically investigated optical properties of ${\mathrm{Nd}}_{1-x}{\mathrm{Sr}}_x{\mathrm{MnO}}_3$ single crystals ( $x=0.40\mathrm{}$, 0.50, 0.55, and 0.65). They are similar in their spin-orbital (SO) disordered states at room temperature. At low temperature, the crystals enter into various SO ordered states, i.e., $F$-, $\mathrm{CE}$-, $A$-, and $C$-type orderings, and their mid-infrared absorptions become quite different. The remarkable variation can be explained by polaron dynamics which depend on the ordering patterns. This SO pattern dependent polaron model can also explain the pseudo CE-type ordering case, demonstrating that this scheme can explain the carrier dynamics in complex SO configurations.