  We study the optical properties of the layered rhodium oxide K0.49RhO2, which
is isostructural to the thermoelectric material NaxCoO2. The optical
conductivity shows broad interband transition peaks as well as a low-energy
Drude-like upturn, reminiscent of the optical spectra of NaxCoO2. We find that
the peaks clearly shift to higher energies with respect to those of NaxCoO2,
indicating a larger crystal-field splitting between eg and t2g bands in
K0.49RhO2. The Drude weights suggest that the effective mass of K0.49RhO2 is
almost two times smaller than that of NaxCoO2. These differences in electronic
structures and correlation effects between NaxCoO2 and K0.49RhO2 are discussed
in terms of the difference between Co 3d and Rh 4d orbitals.

Strongly Correlated Electrons