  We have performed a systematic photoemission study of the chemical potential
shift as a function of carrier doping in a pnictide system based on
BaFe$_2$As$_2$. The experimentally determined chemical potential shift is
consistent with the prediction of a rigid band shift picture by the
renormalized first-principle band calculations. This leads to an electron-hole
asymmetry (EHA) in the Fermi surface (FS) nesting condition due to different
effective masses for different FS sheets, which can be calculated from the
Lindhard function of susceptibility. This built-in EHA from the band structure,
which matches well with observed asymmetric superconducting domes in the phase
diagram, strongly supports FS near-nesting driven superconductivity in the iron
pnictides.
