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M. Schmidt, Zhe Wang, Ch. Kant, F. Mayr, V. Tsurkan, J. Deisenhofer, and A. Loidl
The class of two-dimensional triangular antiferromagnets ACrO2 shows such interesting features as spin-driven multiferroicity e.g. for A=Cu, Ag [1], unconventional anomalous Hall effect in PdCrO2 [2], and finite but long spin correlation length summarized as "spin-gel states" [3] due to a topological stable point defect - a Z2 vortex for A=Li, Na [4]. We will discuss our results obtained by optical spectroscopy in CuCrX2 (X=O, S). For CuCrO2 we find that the line width of magnon sidebands increases following a modified Arrhenius law, which indicates the presence of Z2 vortices in this compound in agreement with the observations by Kojima et al. [4] in related systems. The similar compound CuCrS2 exhibits a temperature dependent gap-like feature in the reflectivity, indicating a transition to a symmetry-broken state. We will discuss the possible relation between spin-phonon coupling and density wave formation in this system. [1] S. Seki et al., Phys. Rev. Lett. 101, 067294 (2008) [2] H. Takatsu et al., Phys. Rev. Lett. 105, 137201 (2010) [3] H. Kawamura et al., J. Phys. Soc. Jap. 79, 023701 (2010) [4] N. Kojima et al., J. Phys. Soc. Jap. 62, 4137 (1993) |
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