|
KCuF3 is a prototypical quasi-one-dimensional antiferromagnetic Heisenberg spin S=1/2 chain and serves (together with LaMnO3) as a benchmark system for realistic band-structure calculations of orbitally ordered systems [1,2]. Astonishingly, basic experimental properties such as the optical properties and the dynamic spin susceptibility have either not been reported or could not be reconciled with the crystal structure. We show that the peculiarities of the spin relaxation require a dynamical form of the antisymmetric anisotropic spin-spin interaction. This dynamical Dzyaloshinsky-Moriya interaction is related to strong oscillations of the bridging fluorine ions perpendicular to the crystallographic c axis and allows to resolve consistently the controversies in observation of the magnetic and structural properties of this model system [3]. Moreover, we report on the first optical measurements in KCuF3. The crystal-field excitations of the Cu2+ ions have been observed and their temperature dependence can be understood in terms of magnetic and exchange-induced dipole mechanisms and vibronic interactions[4]. Above TN we observe a new temperature scale TS characterized by the emergence of narrow absorption features that correlate with changes of the orbital ordering as observed by Paolasini et al. [5]. The appearance of these optical transitions provides evidence for a symmetry change above the Néel temperature that affects the orbital ordering and paves the way for the antiferromagnetic ordering. We will also discuss the appearance of double-exciton transitions in this compound. [1] I. Leonov et al.,PRL 101, 096405 (2008) [2] E. Pavarini et al., PRL 101, 266405 (2008) [3] M. Eremin et al., PRL 101, 147601 (2008) [4] J. Deisenhofer et al. PRL 101, 157406 (2008) [5] L. Paolasini et al., PRL 88, 106403 (2002) |
|