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arXiv · 0802.0721

Phonon softening and "forbidden" mode observed by Raman scattering in Na0.5CoO2

Q. M. Zhang·M. an·S. K. Yuan·Y. Wu·D. Wu·J. L. Luo·N. L. Wang·W. Bao·Y. N. Wang
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Abstract

Polarized Raman scattering measurements have been performed on Na0.5CoO2 single crystal from 8 to 305 K. Both the A1g and E1g phonon modes show a softening below Tc1 ~ 83 K. Additionally, the A1g phonon mode, which is forbidden in the scattering geometry of cross polarization for the triangular CoO2 layers, appears below Tc1. In contrast, the metal-insulator transition at Tc2 ~ 46 K has only secondary effect on the Raman spectra. The phonon softening and the ``forbidden'' Raman intensity follow closely magnetic order parameter and the gap function at the Fermi surface, indicating that the distortion of CoO6 octahedra at Tc1, instead of the Na ordering at ~350 K, is the relevant structural component of the 83 K phase transition.

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Q. M. Zhang, M. an, S. K. Yuan, Y. Wu, D. Wu, J. L. Luo, N. L. Wang, W. Bao, Y. N. Wang. 2008-02-05. Phonon softening and "forbidden" mode observed by Raman scattering in Na0.5CoO2. https://doi.org/10.1103/physrevb.77.045110

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