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Dresden 2011 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 41: CE: Spin Systems and Itinerant Magnets 1

TT 41.1: Talk

Wednesday, March 16, 2011, 18:15–18:30, HSZ 105

Orbital fluctuations versus classical orbital order in RVO3 studied via optical spectral weight — •Julia Küppersbusch1, Agung Nugroho2, Thomas Palstra2, and Markus Grüninger11Universtität zu Köln — 2Rijksuniversiteit Groningen

Spin and orbital degrees of freedom play a decisive role in the low-energy physics of strongly correlated transition-metal oxides. Whereas the spin is a true low-energy degree of freedom with propagating low-energy excitations, it is still questionable if the same holds true for the orbital degree of freedom. In a typical situation the orbitals are strongly coupled to the lattice, which makes it sufficient to consider classical orbitals with rigid orbital order. However, different groups have pointed out that orbital fluctuations may be strong in the 3d2 Mott-Hubbard insulators RVO3 (R = rare earth ion or Y).
Optical spectroscopy offers an efficient method to study the nature of the orbital degree of freedom, because the spectral weight of excitations across the Mott-Hubbard gap depends sensitively on nearest-neighbor orbital-orbital correlations. We study the temperature dependence of the optical spectral weight by means of ellipsometry in the frequency range 0.75 - 5.5 eV. By comparing our experimental results for R = Y, Gd, and Ce with a theory which calculates the temperature dependence of the optical spectral weight based on a low-energy spin-orbital superexchange Hamiltonian [1,2], we draw a conclusion about the nature of the orbital degree of freedom in RVO3.
G. Khaliullin, P. Horsch, and A.M. Oles, Phys. Rev. B 70, 195103 (2004)
A. M. Oles et al. Phys. Rev. B 72, 214431 (2005)

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