Stark-induced anapole magnetic fields in atoms.

Abstract

We show that a paramagnetic atom with spin polarization S, in an electric field E, will have an anapole moment in the direction E\ifmmode\times\else\texttimes\fi{}S, with magnitude of order \ensuremath{\alpha}${\mathit{Ea}}_{0}^{4}$. There is a corresponding toroidal magnetic field inside the atom in the direction r\ifmmode\times\else\texttimes\fi{}(E\ifmmode\times\else\texttimes\fi{}S), with strength of order \ensuremath{\alpha}E. As an example, we evaluate exactly the toroidal field and its anapole moment for hydrogenic atoms to first order in E, using both the Schr\odinger and Dirac equations. We also use the calculated electric polarizabilities to estimate the toroidal magnetic fields and anapole moments for the ground states of the alkali-metal atoms and for Rydberg states. We show that the Stark-induced toroidal magnetic fields of atoms will have no influence on their hyperfine structure. However, they can change the direction of the nuclear spins of electron-spin polarized molecules.