Electronic structure and thermoelectric properties of a layered cobalt oxide Na{sub}xCoO{sub}2 (0.5 < x < 0.8) investigated by angle-resolved photoemission spectroscopy

摘要

Angle resolved photoemission spectroscopy (ARPES) with a synchrotron radiation as an incident photon source was performed on the layered cobalt oxides Na{sub}0.8CoO{sub}2. The measured electronic structure was compared with that of the Na{sub}0.7CoO{sub}2 previously reported. The observed energy-momentum dispersion of the Na{sub}0.8CoO{sub}2 was essentially the same with that of the Na{sub}0.7CoO{sub}2 except for the small difference in the chemical potential Δμ～15 meV, which was caused by the difference in the sodium concentration. By employing the spectral conductivity reported for the Na{sub}0.7CoO{sub}2 and assuming the rigid band model, we calculated the thermoelectric power of the Na{sub}0.8CoO{sub}2. The measured thermoelectric power was quantitatively reproduced by the calculated one as well as that reported for the Na{sub}0.7CoO{sub}2. It is concluded that the scenario of the large thermoelectric power induced by the Boltzman-type electrical conduction in the characteristic bands previously proposed for the Na{sub}0.7CoO{sub}2 is applicable for the Na{sub}0.8CoO{sub}2.