Systematic ARPES study on high Na-level Na$_{x}$CoO$_{2}$ (x$>$0.75)

The phase diagram of the cobaltae Na$_{x}$CoO$_{2}$, with varying Na concentration x, is very rich and complicated. At the high-doping regime (x$>$0.75), the system was found to be more correlated, with a spin-density-wave state emerging at low temperatures. A previous ARPES study has observed a usually large Fermi surface which apparently violates the Luttinger theorem at x = 0.8. We will report our recent ARPES results of the high Na-level Na$_{x}$CoO$_{2}$ (x$>$0.75) samples.