title: Optical evidence for symmetry changes above the Néel temperature of KCuF3.
abstract: We report on optical measurements of the 1D Heisenberg antiferromagnet 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. 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. [Phys. Rev. Lett. 88, 106403 (2002)]. 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.
authors.affiliation: Département de Physique de la Matière Condensée, Université de Genève, CH-1211 Genève 4, Switzerland.
authors.forename: J
authors.initials: J
authors.lastname: Deisenhofer
authors.forename: I
authors.initials: I
authors.lastname: Leonov
authors.forename: M V
authors.initials: MV
authors.lastname: Eremin
authors.forename: Ch
authors.initials: Ch
authors.lastname: Kant
authors.forename: P
authors.initials: P
authors.lastname: Ghigna
authors.forename: F
authors.initials: F
authors.lastname: Mayr
authors.forename: V V
authors.initials: VV
authors.lastname: Iglamov
authors.forename: V I
authors.initials: VI
authors.lastname: Anisimov
authors.forename: D
authors.initials: D
authors.lastname: van der Marel