Determination of $t_{2g}$ Complex in Na$_{x}$CoO$_{2}$ by Angle-Resolved Photoemission Spectroscopy

A systematic investigation on $t_{2g}$ complex in Na$_x$CoO$_2$ is carried by ARPES. By taking advantage of the matrix element effect, we recover and trace the dispersion of all three $t_{2g} $ bands for different Na concentration ($x=0.3\sim0.7$). The dispersion ``kink'' we observed before is found to be cause by the hybridization between $a_{1g}$ and $e'_{g}$ bands. This band hybridization forms a narrow band near the Fermi level, which causes a large mass renormalization. The width of the non- hybridized bands is about half of the one predicted by LDA calculations, which is possibly due to the correlation effect.