Anomalous Variation of Optical Spectra with Spin Polarization in Double-Exchange Ferromagnet: ${\mathrm{La}}_{1-\mathit{x}}{\mathrm{Sr}}_{\mathit{x}}{\mathrm{MnO}}_3$

Optical spectra and their temperature dependence have been investigated for a prototypical double-exchange ferromagnet ${\mathrm{La}}_{1-x}{\mathrm{Sr}}_x{\mathrm{MnO}}_3$ ( $x=0.175\mathrm{}$). The optical conductivity spectrum above $T_c$ is characterized by interband transitions between the exchange-split bands and gradually changes into intraband excitations with decrease of temperature, accompanied by conspicuous transfer of spectral weight over a wide energy region of 0–3 eV. The results indicate a large variation of the electronic structure with the spin polarization of the conduction carriers.