Mid-infrared optical conductivity spectra of Nd_1-xSr_xMnO₃: Orbital pattern dependent polaron hopping

We investigated temperature-dependent optical conductivity spectra σ(ω) of Nd_1-xSr_xMnO₃ (x = 0.40, 0.50, 0.54, and 0.65) single crystals. At room temperature, mid-infrared σ(ω) are nearly the same for all compositions and spectral weights seem to depend only on the doping concentration. At low temperature, however, σ(ω) are quite different and spectral weights seem to strongly depend on the orbital/spin patterns, i.e., F (x = 0.40), CE (x = 0.50), A (x = 0.54), and C (x = 0.65)-type. We will discuss the strong doping dependence of the mid-infrared optical conductivity spectra in terms of the orbital pattern dependent Jahn-Teller polaron hopping.