The number of absorption and Raman optical modes for each Wyckoff orbit in the high-temperature tetragonal (I4/mmm) parent lattice of the Ruddlesden-Popper compounds Ca3X2O7, with X=Mn or X=Ti is given. We analyze the effect of sequential perturbations which lower the symmetry to Cmcm and Cmc21 and finally include magnetic ordering. We determine the power law behavior (within mean field theory) for the cross section for photon absorption and Raman scattering of modes which appear as the symmetry is successively lowered. In the Cmc21 phase we give a symmetry analysis to discuss the magnon-phonon coupling which in other systems gives rise to "electromagnons." From our results we suggest several experiments to clarify the phase diagram and other properties of these systems.
@article{arxiv.1011.6672,
title = {Phonons and their Coupling to Magnons in n=2 Ruddlesden-Popper Compounds},
author = {A. B. Harris},
journal= {arXiv preprint arXiv:1011.6672},
year = {2011}
}
Comments
40 pages, 8 figures. Most of the changes are cosmetic (for instance the notation is probably better now). Also the role of several instances of the same irrep is treated in a more explicit way