Physics – Condensed Matter – Strongly Correlated Electrons
Scientific paper
2005-03-31
J. Phys. Soc. Jpn. 75, 1954 (2005).
Physics
Condensed Matter
Strongly Correlated Electrons
4 pages, 3 figures, submitted to J. Phys. Soc. Jpn
Scientific paper
10.1143/JPSJ.74.1954
Optical conductivity [$\sigma(\omega)$] of the Kondo semiconductor YbB$_{12}$ has been measured over wide ranges of temperature ($T$=8$-$690 K) and photon energy ($\hbar \omega \geq$ 1.3 meV). The $\sigma(\omega)$ data reveal the entire crossover of YbB$_{12}$ from a metallic electronic structure at high $T$ into a semiconducting one at low $T$. Associated with the gap development in $\sigma(\omega)$, a clear onset is newly found at $\hbar\omega$=15 meV for $T \leq$ 20 K. The onset energy is identified as the gap width of YbB$_{12}$ appearing in $\sigma(\omega)$. This gap in \sigma(\omega)$ is interpreted as the indirect gap, which has been predicted in the band model of Kondo semiconductor. On the other hand, the strong mid-infrared (mIR) peak observed in $\sigma(\omega)$ is interpreted as arising from the direct gap. The absorption coefficient around the onset and the mIR peak indeed show characteristic energy dependences expected for indirect and direct optical transitions in conventional semiconductors.
Iga Fumitoshi
Kimura Sachie
Michizawa T.
Nanba Takao
Okamura Hidekzu
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