  Layered misfit cobaltate [Ca$_2$CoO$_3$]$_{0.62}$[CoO$_2$], which emerged as
an important thermoelectric material~[A. C. Masset et al. Phys. Rev. B, 62, 166
(2000)], has been explored extensively in the last decade for the exact
mechanism behind its high Seebeck coefficient. Its complex crystal and
electronic structures have inhibited consensus among such investigations. This
situation has arisen mainly due to difficulties in accurate identification of
the chemical state, spin state, and site symmetries in its two subsystems
(rocksalt [Ca$_2$CoO$_3$] and triangular [CoO$_2$]). By employing resonant
photoemission spectroscopy and x-ray absorption spectroscopy along with charge
transfer multiplet simulations (at the Co ions), we have successfully
identified the site symmetries, valencies and spin states of the Co in both
layers. Our site-symmetry observations explain the experimental value of the
high Seebeck coefficient and also confirm that the carriers hop within the
rocksalt layer, which is in contrast to earlier reports where hopping within
triangular CoO$_2$ layer has been held responsible for the large Seebeck
coefficient.

Strongly Correlated Electrons