Abstract
Borromean rings and Borromean binding, a class of intriguing phenomena as three objects are linked (bound) together while any two of them are unlinked (unbound), widely exist in nature and have been found in systems of biology, chemistry and physics. Previous studies have suggested that the occurrence of such a binding in physical systems typically relies on the microscopic details of pairwise interaction potentials at short-range, and is therefore non-universal. Here, we report a new type of Borromean binding in ultracold Fermi gases with Rashba spin-orbit coupling, which is {\it universal} against short-range interaction details, with its binding energy only dependent on the s-wave scattering length and the spin-orbit coupling strength. We show that the occurrence of this universal Borromean binding is facilitated by the symmetry of the single-particle dispersion under spin-orbit coupling, and is therefore {\it symmetry-selective} rather than interaction-selective. The state is robust over a wide range of mass ratio between composing fermions, which are accessible by Li-Li, K-K and K-Li mixtures in cold atoms experiments. Our results reveal the importance of symmetry factor in few-body physics, and shed light on the emergence of new quantum phases in a many-body system with exotic few-body correlations.
Highlights
Previous studies have suggested that the occurrence of such a binding in physical systems typically relies on the microscopic details of pairwise interaction potentials at short range and is, nonuniversal
We report a new type of Borromean binding in ultracold Fermi gases with Rashba spin-orbit coupling, which is universal against short-range interaction details, with its binding energy only dependent on the s-wave scattering length and the spin-orbit-coupling strength
We show that the occurrence of this universal Borromean binding is facilitated by the symmetry of the single-particle dispersion under spin-orbit coupling and is, symmetry selective rather than interaction selective
Summary
The fascinating topological structure of Borromean rings has attracted much attention in biology [1] and chemistry [2], while, in physics, their quantum mechanical analog, the Borromean binding, has been reported in halo nuclei 6He and 11Li [3,4] and in ultracold atomic gases [5,6,7,8,9,10,11,12,13,14] manifested as the Efimov effect [15,16]. Energies as well as the locations of their emergence [16] In all these studies, the Borromean binding appears to be a nonuniversal phenomenon that inevitably relies on the short-range details of interaction potentials. The Borromean binding appears to be a nonuniversal phenomenon that inevitably relies on the short-range details of interaction potentials This nonuniversality makes a unified understanding of the Borromean binding conceptually difficult and renders its experimental detection inconveniently system dependent. We identify the existence of such bindings in a wide range of mass ratios between composing fermions, which are readily accessible by Li-Li, K-K, and K-Li mixtures in current cold-atom experiments The robustness of this Borromean binding suggests the importance of the single-particle spectral symmetry in few-body physics, which has rarely been discussed before
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