Optical evidence for symmetry changes above the Néel temperature of KCuF3.

Phys Rev Lett

Département de Physique de la Matière Condensée, Université de Genève, CH-1211 Genève 4, Switzerland.

Published: October 2008

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.

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http://dx.doi.org/10.1103/PhysRevLett.101.157406DOI Listing

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