Systematic doping evolution of quasiparticle mode and Fermi surface topology in NaxCoO$_2$

We have carried out a detailed and systematic state-of-the-art photoemission study of NaxCoO$_2$ over a wide range of doping. The Fermi velocity is found to be weakly anisotropic and small leading to a strongly suppressed quasiparticle bandwidth as a universal behavior in all dopings. No surface state or Ruthanate-type reconstruction is observed. Systematic studies show that the 2-D Fermi-surface area evolves according to the Na doping count only below x=0.5. The measured Fermi surface topology near superconducting Na doping kinematically allows for commensurate fluctuations (charge or lattice) as potential competing instabilities. The temperature evolution of quasiparticles will be discussed in addition.