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Magnetismus Poster: Do., 13:00–15:30 D-P217
Role of the orbital-lattice interaction in multiferroic behavior
M. Bastjan 1 , A. Rusydi 1 , G. Neuber 1 , S. Singer 1 , M. Ruebhausen 1 , D.N.
Argyriou 2 , N. Aliouane 2 , M. Kim 3 , H. Barath 3 , S.L. Cooper 3
1 Insitut für Angewandte Physik, Universität Hamburg – 2 Hahn Meitner Institut, Berlin
– 3 University of Illinois at Urbana-Champaign, USA
We have investigated the temperature dependence of the orbital, structural, and magnetic
ordering in TbMnO3 by spectral ellipsometry, VUV reflectance, XAS, and Raman
scattering in order to reveal the mechanism that leads to the symmetry breaking responsible
for the multiferroic behavior. We find a pronounced redistribution of spectral
weight below TN = 41 K in the optical spectra. We observe additional precursor effects
in the spectra above TN . For incident photon energies of 1.91 eV in resonance with d
- d transitions, we find a renormalization in the Raman spectra of the Jahn - Teller
mode below TN and new soft mode below Tf , where TbMnO3 becomes multiferroic.
In the VUV-reflectance spectra we analyze thermal difference spectra and find changes
at the transition into the magnetic state at energies of 8,12, and 18 eV. The transition
at 18 eV is most likely connected to the O2s-O2p transition. More details are revealed
in the XAS spectra. We interpret our results as a strong evidence for the formation of
an unconventional soft mode as a consequence of the interplay between the electronic
correlations and the electron-phonon interaction.