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Charge ordering and magneto-polarons in Na$_{0.82}$CoO$_2$

C. Bernhard·A. V. Boris·N. N. Kovaleva·G. Khaliullin·A. Pimenov·L. Yu·D. P. Chen·C. T. Lin·B. Keimer
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Abstract

Using spectral ellipsometry, we have measured the dielectric function of a Na$_{0.82(2)}$CoO$_2$ crystal that exhibits bulk antiferromagnetism with T$_{N}$=19.8 K. We identify two prominent transitions as a function of temperature. The first one at 280 K involves marked changes of the electronic and the lattice response that are indicative of charge ordering in the CoO$_{2}$ layers. The second transition coincides with T$_{N}$=19.8 K and reveals a sizeable spin-charge coupling. The data are discussed in terms of charge ordering and formation of magneto-polarons due to a charge-induced spin-state transition of adjacent Co$^{3+}$ ions.

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C. Bernhard, A. V. Boris, N. N. Kovaleva, G. Khaliullin, A. Pimenov, L. Yu, D. P. Chen, C. T. Lin, B. Keimer. 2004-03-04. Charge ordering and magneto-polarons in Na$_{0.82}$CoO$_2$. https://doi.org/10.1103/physrevlett.93.167003

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