The effect of lattice distortion and orbital mixing on the optical and   magnetic properties of cubic RMnO$sub 3$ (R = La, Pr, Nd, Gd, Tb)
  We investigated the $ab$-plane absorption spectra of $R$MnO$%_{3}$ ($R$ = La, Pr, Nd, Gd, and Tb) thin films. As the $R$-ion size decreases, we observed a drastic suppression of the 2 eV peak, \textit{i.e.} the inter-site optical transition between spin- and orbital-aligned states across the Mott gap. We found that both lattice distortion and the corresponding orbital mixing of the ordered orbital state should play an important role in the 2 eV peak suppression. We also found that the 2 eV spectral weight is proportional to the $A$-type antiferromagnetic ordering temperature, which suggests that the magnetic interaction might be sensitively coupled to the orbital mixing. 
M. W. Kim, S. J. Moon, J. H. Jung, Jaejun Yu, Sachin Parashar, P.   Murugavel, T. W. Noh