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Optical investigations on $Y_{2-x} Bi_x Ru_2 O_7$: Electronic structure evolutions related to the metal-insulator transition

J. S. Lee·S. J. Moon·T. W. Noh·T. Takeda·R. Kanno·S. Yoshii·M. Sato
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Abstract

Optical conductivity spectra of cubic pyrochlore $Y_{2-x} Bi_x Ru_2 O_7$ (0.0$\leq ${\it x}$\leq $2.0) compounds are investigated. As a metal-insulator transition (MIT) occurs around {\it x}$=$0.8, large spectral changes are observed. With increase of {\it x}, the correlation-induced peak between the lower and the upper Hubbard bands seems to be suppressed, and a strong mid-infrared feature is observed. In addition, the $p-d$ charge transfer peak shifts to the lower energies. The spectral changes cannot be explained by electronic structural evolutions in the simple bandwidth-controlled MIT picture, but are consistent with those in the filling-controlled MIT picture. In addition, they are also similar to the spectral changes of Y$_{2-x}$Ca$_{x}$Ru$_{2}$O$_{7}$ compounds, which is a typical filling-controlled system. This work suggests that, near the MIT, the Ru bands could be doped with the easily polarizable Bi cations.

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J. S. Lee, S. J. Moon, T. W. Noh, T. Takeda, R. Kanno, S. Yoshii, M. Sato. 2005-04-25. Optical investigations on $Y_{2-x} Bi_x Ru_2 O_7$: Electronic structure evolutions related to the metal-insulator transition. https://doi.org/10.1103/physrevb.72.035124

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