Energy Scaling of Cold Atom-Atom-Ion Three-Body Recombination

We study three-body recombination of Ba⁺+Rb+Rb in the mK regime where a single ¹³⁸Ba⁺ ion in a Paul trap is immersed into a cloud of ultracold ⁸⁷Rb atoms. We measure the energy dependence of the three-body rate coefficient k₃ and compare the results to the theoretical prediction, k₃∝Ecol-3/4, where Ecol is the collision energy. We find agreement if we assume that the nonthermal ion energy distribution is determined by at least two different micromotion induced energy scales. Furthermore, using classical trajectory calculations we predict how the median binding energy of the formed molecules scales with the collision energy. Our studies give new insights into the kinetics of an ion immersed in an ultracold atom cloud and yield important prospects for atom-ion experiments targeting the s-wave regime.