Optical evidence for symmetry changes above the Néel temperature of KCuF3.
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.
Deisenhofer
J
J
Département de Physique de la Matière Condensée, Université de Genève, CH-1211 Genève 4, Switzerland.
Leonov
I
I
Eremin
M V
MV
Kant
Ch
Ch
Ghigna
P
P
Mayr
F
F
Iglamov
V V
VV
Anisimov
V I
VI
van der Marel
D
D