H. Okamura et al., Optical conductivity of Yb1-xLuxB12: Energy gap and mid-infrared peak in diluted Kondo semiconductors, PHYS REV B, 62(20), 2000, pp. R13265-R13269
We have measured the optical conductivity sigma(omega) of Yb1-xLuxB12 (0 le
ss than or equal tox less than or equal to1), where the system evolves from
a Kondo semiconductor at x=0 to a nonmagnetic metal at x=1; For x=0, sigma
(omega) exhibits a clear energy gap with an onset at similar to 20 meV and
a shoulder at 38 meV. As. x increases, the gap:is rapidly filled in from th
e bottom, while the shoulder remains at similar to 40 meV up to x = 1/2. Th
ese results suggest that Lu substitution into YbB12 produces an in-gap band
, but the characteristic energy for the gap remains unchanged in a wide ran
ge of x. Spectral evolutions of a characteristic mid-infrared peak, which r
esults from Yb 4f-derived states near the Fermi level, suggest a strong cou
pling of Yb 4f electrons with conduction electrons.