Abstract
We report on optical measurements of the 1D Heisenberg antiferromagnet . The crystal-field excitations of the ions have been observed and their temperature dependence can be understood in terms of magnetic and exchange-induced dipole mechanisms and vibronic interactions. Above we observe a new temperature scale 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.
- Received 13 April 2007
DOI:https://doi.org/10.1103/PhysRevLett.101.157406
©2008 American Physical Society