|
In this talk I will present an overview of the recent studies on the role of the orbital degrees of freedom in the dynamic properties of the strongly correlated systems. While the role of orbitals in stabilizing peculiar layered or chain-like magnetic structures in the cubic perovskites is well investigated, the low energy dynamics of the orbital degrees o freedom is far from being understood. This is firstly because the so-called orbiton (excitation from the orbitally ordered state) is extremely hard to detect experimentally. However, in this talk I will report on the very recent observation of such an excitation in the resonant inelastic x-ray scattering of Sr2CuO3 [1]. Here this first really unambiguous direct observation of the dispersive orbital excitation has been supported by an extensive theoretical calculation which inter alia used a novel idea of the separation of spin and orbital degree of freedom in this one-dimensional system. Besides, I will also explain how the presence of the t2g orbital degrees of freedom topologically constrains the motion of a hole [2], switches off the quantum spin fluctuations [3] and therefore alters in this case the commonly accepted picture of the hole moving as a spin polaron when doped into an ordered antiferromagnet. As this inevitably has consequences for the physics of lightly doped cubic vanadates such as La1-xSrxVO3, it will be shown how the presence of the orbital excitations can then be detected indirectly.
[1] J. Schlappa, K. Wohlfeld, K. J. Zhou, M. W. Haverkort, V. Strocov, S. Nishimoto, H. Ronnow, L. Hozoi, T. Schmitt, and J. van den Brink [in preparation (2010)]. [2] K. Wohlfeld, M. Daghofer, A. M. Oles and P. Horsch, Phys. Rev. B 78, 214423 (2008). [3] K. Wohlfeld, A. M. Oles and P. Horsch, Phys. Rev. B 79, 224433 (2009); see also accompanying viewpoint written by M. Berciu in Physics 2, 55 (2009). |
|