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Optical properties and electronic structure of ZrB$_{12}$

J. Teyssier·A. B. Kuzmenko·D. van der Marel·F. Marsiglio·A. B. Liashchenko·V. Filippov·N. Shitsevalova
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Abstract

We report optical (6 meV - 4 eV) properties of a boride superconductor ZrB$_{12}$ ($T_c$ = 6 K) in the normal state from 20 to 300 K measured on high-quality single crystals by a combination of reflectivity and ellipsometry. The Drude plasma frequency and interband optical conductivity calculated by self-consistent full-potential LMTO method agree well with experimental data. The Eliashberg function $α_{tr}^2F(ω)$ extracted from optical spectra features two peaks at about 25 and 80 meV, in agreement with specific heat data. The total coupling constant is $λ_{tr}=1.0\pm0.35$. The low energy peak presumably corresponds to the displacement mode of Zr inside $B_{24}$ cages, while the second one involves largely boron atoms. In addition to the usual narrowing of the Drude peak with cooling down, we observe an unexpected removal of about 10 % of the Drude spectral weight which is partially transferred to the region of the lowest-energy interband transition ($\sim$ 1 eV). This effect may be caused by the delocalization of the metal ion from the center of the $B_{24}$ cluster.

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J. Teyssier, A. B. Kuzmenko, D. van der Marel, F. Marsiglio, A. B. Liashchenko, V. Filippov, N. Shitsevalova. 2007-01-30. Optical properties and electronic structure of ZrB$_{12}$. https://doi.org/10.1103/physrevb.75.134503

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