Electronic structure and charge transfer processes in a Bi-Ca misfit cobaltate

We report polarization-dependent on-resonance and off-resonance photoemission and x-ray absorption measurements to probe the character and the symmetry of the occupied and empty valence-band (VB) states of the four-layered misfit cobaltate [Bi2Ca2O4](RS)center dot[CoO2](1.67). These experiments bring clear evidence that the one-electron removal VB photoemission spectra, between the Fermi energy (E-F) and similar to 4.5 eV, contain Co 3d states, which are strongly hybridized with O 2p states in the binding energy region of similar to 1.8-similar to 4.5 eV below EF. The states at the Fermi energy have a(1g) out-of-plane symmetry. In addition, by tuning the incident photon energy across the Co 2p(3/2)-> Co 3d (a(1g)) threshold and the O 1s -> O 2p-Co 3d (a(1g)) hybridized threshold, both found at similar to 2 eV below the absorption edge maximum, it is possible to observe a transition from a Raman regime to an Auger regime. From this transition the charge transfer dynamics from the Co 3d to the O 2p states and from the O 2p to the Co 3d states have been estimated to be similar to 3 and similar to 3.3 fs, respectively. This combined information suggests an electron hopping process between neighboring Co a(1g) states across E-F and mediated by O 2p states with suitable symmetry.