Within a recently proposed variational approach it has been shown that, in La12xAxMnO3 perovskites with 0,x,0.5, near the metal-insulator transition, the combined effect of the magnetic and electron-phonon interactions pushes the system toward a regime of two coexisting phases: a low electron density one made by itinerant large polarons forming ferromagnetic domains and a high electron density one made by localized small polarons giving rise to paramagnetic or antiferromagnetic domains depending on temperature. Employing the above-mentioned variational scheme, in this paper spectral and optical properties of manganites are derived for x50.3 at different temperatures. It is found that the phase separation regime induces a robust pseudogap in the excitation spectrum of the system. Then the conductivity spectra are characterized by a transfer of spectral weight from high to low energies, as the temperature T decreases. In the metallic ferromagnetic phase, at low T two types of infrared absorption come out: a Drude term and a broad absorption band due respectively to the coherent and incoherent motion of large polarons. The obtained results turn out in good agreement with experiments.
Spectral properties and infrared absorption in manganites / Perroni, CARMINE ANTONIO; De Filippis, G.; Cataudella, V.; G., Iadonisi. - In: PHYSICAL REVIEW. B, CONDENSED MATTER AND MATERIALS PHYSICS. - ISSN 1098-0121. - ELETTRONICO. - (2001), pp. 144302-1-144302-17. [10.1103/PhysRevB.64.144302 PACS: 71.30.+h]