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

TL;DR

This paper investigates the effective electric fields in weakly polar molecules for electron EDM searches, revealing that certain hydrides have larger Eeff than fluorides due to orbital mixing, challenging previous assumptions.

Contribution

It demonstrates that molecules with smaller polarization can have larger Eeff because of valence orbital mixing, providing new insights for selecting molecules in eEDM experiments.

Findings

YbH and HgH have larger Eeff than their fluoride counterparts.

Orbital mixing significantly influences Eeff beyond polarization considerations.

Relativistic calculations reveal non-intuitive relationships between polarization and Eeff.

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 (Eeff) of a target molecule. Hence, an analysis of the quantities that enhance Eeff 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 Eeff. However, our Dirac-Fock and relativistic coupled-cluster singles and doubles calculations show that the hydrides of Yb and Hg have larger Eeff 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.