Spin-Controlled Mott-Hubbard Bands inLaMnO3Probed by Optical Ellipsometry

Abstract

Spectral ellipsometry is used to determine the dielectric function of an untwinned crystal of ${\mathrm{L}\mathrm{a}\mathrm{M}\mathrm{n}\mathrm{O}}_3$ in the range 0.5–5.6 eV at temperatures $50\le T\le 300\mathrm{K}$. A pronounced redistribution of spectral weight is found at the Néel temperature $T_N=140\mathrm{K}$. The anisotropy of the spectral weight transfer matches the magnetic ordering pattern. A superexchange model quantitatively describes spectral weight transfer induced by spin correlations. This analysis implies that the lowest-energy transitions around 2 eV are intersite $d$-$d$ transitions, and that ${\mathrm{L}\mathrm{a}\mathrm{M}\mathrm{n}\mathrm{O}}_3$ is a Mott-Hubbard insulator.