Screening effect of nucleon electric dipole moments in atomic system.

We examine the screening effect of nucleon electric dipole moments (EDMs) and the nuclear EDM in an atom. The interactions of the nucleon EDMs with the electrons and protons induce the atomic EDM that survives the screening thanks to the nuclear finite-size effect. Since the leading-order contribution vanishes for spin $ \frac{ 1 }{ 2 } $ nuclei, we evaluate the next-to-leading order contribution in $^{199}$Hg. The numerical result implies a lower sensitivity of the atomic EDM on the neutron EDM in comparison with a previous calculation based on a simple expansion of the Schiff moment operator.