Optical investigation of LaMnO3 thin films: a study of the 2-eV band

We measure the transmittance of LaMnO 3 (LMO) thin films in the spectral range from 10 000 to 38 000 cm -1 as a function of temperature. The optical conductivity obtained from the transmittance data is decomposed into five Drude-Lorentz contributions: three of them show evident changes below the Neel temperature T N $\simeq$ 140 K. We discuss the band assignment in the framework of the tight-binding and of the orbitally degenerate Hubbard models. Our results ascribe the overall low-frequency spectrum of LMO to charge-transfer mechanisms involving the t 2g and e g electrons of the Mn ions, without invoking the presence of excitonic contributions. This finding definitely promotes a Mott-Hubbard scenario for LMO and provides an estimate of the Hamiltonian parameters. Copyright EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg 2011