Ion solvation in atomic baths: from snowballs to polarons

Abstract

Solvation, the result of the complicated interplay between solvent-solute and solvent-internal interactions, is one of the most important chemical processes. Consequently, a complete theoretical understanding of solvation seems a heroic task. However, it is possible to elucidate fundamental solvation mechanisms by looking into simpler systems, such as ion solvation in atomic baths. In this work, we study ion solvation by calculating the ground state properties of a single ion in a neutral bath from the high-density regime to the low-density regime, finding common ground for these two, in principle, disparate regimes. Our results indicate that a single $^{174}$Yb$^+$ ion in a bath of $^{7}$Li atoms forms a coordination complex at high densities with a coordination number of 8, with strong electrostriction, characteristic of the snowball effect. On the contrary, treating the atomic bath as a dilute quantum gas at low densities, we find that the short range of the ion-atom interaction plays a significant role in the physics of many-body bound states and polarons. Furthermore, in this regime, we explore the role of a putative ion trap, which drastically affects the binding mechanism of the ion and atoms from a quantum gas. Therefore, our results give a novel insight into the universality of ion-neutral systems in the ultracold regime and the possibilities of observing exotic many-body effects.