Abstract
We have studied orbital dynamics in the spin liquid candidate using multifrequency electron-spin resonance. We prepared two high-quality single crystals. The crystal with a slight copper deficiency shows a structural phase transition at around 200 K due to the cooperative Jahn-Teller effect, accompanied with orbital ordering. In contrast, the crystal with almost perfect stoichiometry shows no orbital ordering down to the lowest temperature of 1.5 K. Dramatic change in the factor anisotropy as a function of frequency and temperature demonstrates orbital quantum fluctuations at a nearly constant time scale of below 20 K, evidencing the emergence of an orbital liquid state in this quantum spin liquid compound.
- Received 3 March 2015
DOI:https://doi.org/10.1103/PhysRevB.92.180410
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