90000413

open access

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Optical conductivity of the Kondo insulator YbB₁₂: Gap formation and low-energy excitations

English (英語)

Physical Review B

58(12)

R7496-R7499

American Physical Society (APS)

1998-09

2007-03-20

Optical reflectivity experiments have been conducted on single crystals of the Kondo insulator YbB₁₂ in order to obtain its optical conductivity, σ(ω). Upon cooling below 70 K, a strong suppression 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 4⁢𝑓-derived states across the gap. In addition, a broad peak is observed at ∼0.25⁢eV. This peak is attributed to transitions between Yb 4⁢𝑓-derived states and the 𝑝−𝑑 band, and is reminiscent of similar peaks previously observed for rare-earth hexaborides.

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