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

We measure the transmittance of LaMnO3 (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 N,el temperature T (N) 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.