Photoemission and x-ray-absorption study of misfit-layered (Bi,Pb)-Sr-Co-Ocompounds: Electronic structure of a hole-doped Co-O triangular lattice - art. no. 115104

We present a photoemission and x-ray-absorption study of the misfit-layered (Bi,Pb)-Sr-Co-O compounds which have a Co-O triangular lattice with a mixe d valence of Co3+ and Co4+. The valence-band photoemission as well as the O 1s and Co 2p x-ray absorption spectra indicate that Co3+ and Co4+ have the low-spin t(2g)(6) and t(2g)(5) configurations, respectively. The angle-res olved photoemission spectra show that the dispersion of the t(2g) feature i s very small compared to its width at each angle, suggesting that the elect ron-lattice coupling energy is much larger than the kinetic energy of the t (2g) electrons and that the carriers in the Co-O triangular lattice are ess entially polarons formed by Co4+ in the nonmagnetic Co3+ background.