Anisotropy in the Interactions of Ultracold Dysprosium*

The ground $4{\rm f}^{10}6{\rm s}^2$ configuration of atomic dysprosium has an unfilled 4f$^{10}$ shell lying beneath a closed 6s$^2$ shell. This so-called ``submerged-shell'' atom has a large orbital ($L$ = 6) and total ($J$ = 8) electron angular momenta and, consequently, an extremely large magnetic moment of $10\mu_B$. Only recently the first laser cooling and trapping experiment of dysprosium atoms has been reported [1]. The experiment suggested that the anisotropy from the submerged shell and magnetic moment plays a significant role in the interactions of dysprosium atoms. Here, we explore the anisotropies from the electrostatic dispersion and magnetic dipole-dipole interactions. We use a relativistic configuration interaction valence-bond method to obtain short-range chemical potentials. Dispersion coefficients have been calculated using known atomic data. Comparison of the strengths of dispersion and magnetic dipole interactions shows that the anisotropy in the dispersion dominates for atomic separations less than 50 bohr and can lead to a rapid reorientation of the Dy angular momenta.\\[4pt] [1] M. Lu, S. Ho Youn, and B. Lev, Phys. Rev. Lett. {\bf 104}, 063001 (2010).