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Optical conductivity of the Kondo insulator YbB_12: Gap formation and low-energy excitations

H. Okamura·S. Kimura·H. Shinozaki·T. Nanba·F. Iga·N. Shimizu·T. Takabatake
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Abstract

Optical reflectivity experiments have been conducted on single crystals of the Kondo insulator YbB_12 in order to obtain its optical conductivity, σ(ω). Upon cooling below 70 K, a strong supression of σ(ω) is seen in the far-infrared region, indicating the opening of an energy gap of ~ 25 meV. This gap development is coincident with a rapid decrease in the magnetic susceptibility, which shows that the gap opening has significant influence on magnetic properties. A narrow, asymmetric peak is observed at ~40 meV in σ(ω), which is attributed to optical transitions between the Yb 4f-derived states across the gap. In addition, a broad peak is observed at ~0.25 eV. This peak is attributed to transitions between Yb 4f-derived states and p-d band, and is reminiscent of similar peaks previously observed for rare-earth hexaborides.

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H. Okamura, S. Kimura, H. Shinozaki, T. Nanba, F. Iga, N. Shimizu, T. Takabatake. 1998-10-13. Optical conductivity of the Kondo insulator YbB_12: Gap formation and low-energy excitations. https://doi.org/10.1103/physrevb.58.r7496

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