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Peter Horsch(a) and Andrzej M. Oles(a,b)
(a) Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, D-70569 Stuttgart, Germany (b) Marian Smoluchowski Institute of Physics, Jagellonian University, Reymonta 4, PL-30059 Krakow, Poland We introduce a model for charged defects in weakly doped Y1-xCaxVO3 perovskites and study their effect on the magnetic and orbital order. Starting from a multiband Hubbard model we show that the charges introduced by doping are bound to the Ca defects with large binding energy of ∼ 1 eV at small doping. The defect states give rise to the mid-infrared absorption band observed in the optical spectroscopy. The defect band is partially filled which allows for disorder controlled activated transport. Next, we explore the effect of bound charge carriers on the dynamics of the {yz,zx} orbital and spin degrees of freedom in the context of a microscopic strong-coupling model [1], and show that the transition from G-type to C-type antiferromagnetic (AF) order is triggered by the kinetic energy of doped holes via a double exchange scenario. Thereby the defect states are responsible for fragmentation of the orbital chains along the ferromagnetic (FM) c axis - some of them contain hole defects while in others charge-orbital coupling suppresses locally {yz,zx} orbital fluctuations. This provides a novel physical mechanism for spin-orbital dimerization along the FM bonds in weakly doped systems which operates even at zero temperature. This mechanism has to be distinguished from the dimerization at finite temperature, which occurs in the FM spin-orbital chains [2], as well as in the C-AF phase of undoped YVO3. [1] P. Horsch, A.M. Oles, L.F. Feiner, G. Khaliullin, Phys. Rev. Lett. 100, 167205 (2008). [2] J. Sirker, A. Herzog, A.M. Oles, P. Horsch, Phys. Rev. Lett. 101, 157204 (2008).} |
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