Electronic properties of Na_xCoO₂

Jochen Geck

Leibniz Institute for Solid State and Materials Research IFW Dresden, Helmholtzstrasse 20, 01069 Dresden, Germany

We present NEXAFS and ARPES studies on NaxCoO2 single crystals with x=0.3, 0.7, 0.75. The temperature and polarization dependent NEXAFS data reveal a low spin state of cobalt in the whole temperature range between 25 K and 370 K. The lowest unoccupied band is shown to be of a1g-character. No evidence for magnetopolarons has been observed in these compounds. We roport high resolution ARPES measurements of the band structure, the Fermi surface and the quasiparticle dispersions of a Na0.7CoO2 single crystal.