Strong linear dichroism in Mn L2,3 absorption predicted for orbital ordering in LaMnO3

The difference in Mn L-2,L-3 X-ray absorption spectrum between polarizations parallel and perpendicular to the c-axis, i.e., linear dichroism (LD), is discussed for LaMnO3, where 3d orbits 3x(2) - r(2) and 3y(2) - r(2) are suggested to align "antiferromagnetically" in the a-b plane. By a calculation on the basis of a single-ion model including the intraatomic 3d-3d and 3d-2p multipole interactions and a crystal field, we show that the basic multiplet structure of the LD spectrum strongly reflects 3d orbital ordering and is insensitive to the Jahn-Teller distortion of the MnO6 octahedra. LD is, therefore, shown to be a promising method to observe directly orbital ordering.