Analysis of large effective electric fields of weakly polar molecules for electron electric-dipole-moment searches

Abstract

The electric dipole moment of an electron (eEDM) is one of the sensitive probes of physics beyond the standard model. The possible existence of the eEDM gives rise to an experimentally observed energy shift, which is proportional to the effective electric field (E eff ) of a target molecule. Hence, an analysis of the quantities that enhance E eff is necessary to identify suitable molecules for eEDM searches. In the context of such searches, it is generally believed that a molecule with larger electric polarization also has a larger value of E eff . However, our Dirac-Fock and relativistic coupled-cluster singles and doubles calculations show that the hydrides of Yb and Hg have larger E eff than those of fluorides, even though their polarizations are smaller. This is due to significant mixing of valence s and p orbitals of the heavy atom in the molecules. This mixing has been attributed to the energy differences of the valence atomic orbitals and the overlap of the two atomic orbitals based on the orbital interaction theory.

Systematic study of relativistic and chemical enhancements of P,T -odd effects in polar diatomic radicals

“…al. studied large eEDM enhancement effects in hydrides within orbital interaction theory and remarked an influence of the energy difference between the interacting valence orbitals of the electronegative atom and the unoccupied p 1/2 orbital of the heavy atom [14]. Both of the mentioned studies confirmed that large contributions of s-and p-type atomic orbitals in the singly occupied molecular orbital increase P, T -odd effects, as expected [12].…”

“…For comparison, instead of the improved relativistic factor for W s (eq. (18)) relation (14) can be used to receive relativistic enhancement factors:…”

Zeroth order regular approximation approach to electric dipole moment interactions of the electron

“…21,22 The theoretical search for still more favourable candidates for eEDM experiments, employing relativistic quantum chemistry, is vivid. [23][24][25][26][27][28][29][30] So far, besides the strong Z-dependence of CP-violating effects, there appears to be no thorough understanding of the mecha-nisms that make eEDM enhancement in molecular systems large, but first attempts in this direction have been reported recently 31 . Thus, a systematic study of P, T -odd effects in molecules is of avail.…”

Role of electron correlation in the P,T -odd effects of CdH: A relativistic coupled-cluster investigation

“…Further, in Ref. [41], the reason for the high value of the P, T molecular parameter in HgH was discussed using the Mulliken population analysis and the orbital interaction theory. The authors of the Ref.…”

“…The authors of the Ref. [41] claimed that the large s-p mixing in the singly occupied molecular orbital increases the effective electric field in a molecule. Thus, large s-p mixing may be one of the reasons for the exceptionally high magnitude of the P, T -odd molecular parameters in HgH.…”