Effect of Orbital Rotation and Mixing on the Optical Properties of Orthorhombic $R{\mathrm{MnO}}_{3}$ ($R=\mathrm{La}$, Pr, Nd, Gd, and Tb)

Effect of Orbital Rotation and Mixing on the Optical Properties of Orthorhombic $R {MnO}_{3}$ ( $R = La$ , Pr, Nd, Gd, and Tb)

M. W. Kim, S. J. Moon, J. H. Jung, Jaejun Yu, Sachin Parashar, P. Murugavel, J. H. Lee, and T. W. Noh

Phys. Rev. Lett. 96, 247205 – Published 20 June 2006

Abstract

We investigated the $a b$ -plane absorption spectra of $R {MnO}_{3}$ ( $R = La$ , Pr, Nd, Gd, and Tb) thin films. As the ionic radius of the $R$ ion decreases, we observed a drastic suppression of the 2 eV peak, i.e., the intersite optical transition between spin- and orbital-aligned states across the Mott gap. We found that, in addition to orbital rotation, orbital mixing in the orbital-ordered state should play an important role in the suppression of 2 eV peak. We also found that the spectral weight of 2 eV peak is proportional to the $A$ -type antiferromagnetic ordering temperature, which suggests that the magnetic interaction should be sensitively coupled to the orbital degree of freedom.