Trimer and Tetramer Bound States in Heteronuclear Systems

The Efimov effect in heteronuclear cold atomic systems is experimentally more easily accessible than the Efimov effect for identical atoms, because of the potentially smaller scaling factor. We focus on the case of two or three heavy identical bosons and another atom. The former case was recently observed in a mixture of ¹³³Cs and ⁶Li atoms. We employ the Gaussian Expansion Method as developed by Hiyama, Kino et al. (Prog Part Nucl Phys 51:223–307, 2003). This is a variational method that uses Gaussians that are distributed geometrically over a chosen range. Supplemental calculations are performed using the Skorniakov–Ter- Martirosian equation. Blume et al. (Phys Rev Lett 113:213201, 2014) previously investigated the scaling properties of heteronuclear systems in the unitary limit and at the three-body breakup threshold. We have completed this picture by calculating the behaviour on the positive scattering length side of the Efimov plot, focussing on the dimer threshold.