discovery of colossal magnetoresistance (CMR) in doped manganese oxides
has attracted a lot of attention to this class of materials because
of its scientific as well as technological relevance . In order to
develop a microscopic understanding of this new phenomenon and of the
underlying interplay between charge, magnetic, and orbital order in
the CMR materials , one could start from a model compound like the
undoped ferromagnetic manganite LaMnO3,
for which calculation of the ARPES spectra have been performed [2-5].
systems would also provide a unique opportunity to study the signatures
of orbital order in the electronic structure and to verify the existence
of qualitatively new excitations, so called orbitons , which correspond
to the perturbation of the orbital order and are predicted to affect
the electron properties (see Fig.1). The dynamics of the orbital excitations
could be studied in great detail by combining ARPES and electron-energy
loss spectroscopy (EELS). However, because LaMnO3 is structurally
3D and only magnetically (electronically) layered, other more two dimensional
compounds ‘isoelectronic’ to the undoped manganites (i.e.,
in the same 3d4 high-spin configuration and for this reason orbitally
ordered) might be better suited for these experiments. In this regard,
the growth of single crystals of potentially suitable systems has already
been started in collaboration with Dr. H. Eisaki, from the AIST-Tsukuba
Research Center in Japan.
 E. Dagotto, T. Hotta, and A. Moreo, Phys. Rep.
344, 1 (2001).
 Y. Tokura and N. Nagaosa, Nature 288, 462 (2000).
 J. van der Brink, P. Horsch, and A.M. Oles, Phys. Rev. Lett. 85,
 V. Perebeinos and P.B. Allen, Phys. Rev. Lett. 85,
 J. Bala et al., Phys. Rev. Lett. 87, 067204
 E. Saitho et al., Nature 410, 180 (2001).