Laboratoire de Physique Théorique
Toulouse - UMR 5152

In many transition metal oxides, different orbital configurations are close in energy or even degenerate. Small changes in temperature or pressure can therefore lead to a complete rearrangement of the electron clouds which in turn also strongly influences the magnetic and the transport properties. An interesting example is YVO_3 which shows a high-temperature phase with C-type antiferromagnetic order but more conventional G-type order at low temperatures. In the C-type phase, neutron scattering [1] has revealed a splitting of the magnon dispersion which points to a dimerization of the magnetic exchange. Numerical calculations [2] for one-dimensional models have shown that a coupling of magnetic and electronic degrees of freedom can indeed lead to a dimerization at finite temperatures even if the ground state is the uniform ferromagnet. Recently, we have shown that such a thermally activated Peierls dimerization is a generic feature of ferromagnetic spin chains and might also be induced by a coupling to phonons [3].

[1] C. Ulrich, G. Khaliullin, JS et al., Phys. Rev. Lett. 91, 257202 (2003) [2] JS, G. Khaliullin, Phys. Rev. B 67, 100408(R) (2003) [3] JS, A. Herzog, A.M. Oles and P. Horsch, Phys. Rev. Lett. (in print), arXiv:0807.4693