paper

How does a synthetic non-Abelian gauge field influence the bound states of two spin-$\half$ fermions?

arXiv:1101.0411 · doi:10.1103/PhysRevB.83.094515

Abstract

We study the bound states of two spin-$\half$ fermions interacting via a contact attraction (characterized by a scattering length) in the singlet channel in 3D space in presence of a uniform non-Abelian gauge field. The configuration of the gauge field that generates a Rashba type spin-orbit interaction is described by three coupling parameters . For a generic gauge field configuration, the critical scattering length required for the formation of a bound state is {\em negative}, i.e. shifts to the "BCS side" of the resonance. Interestingly, we find that there are special high-symmetry configurations (e.g., ) for which there is a two body bound state for {\em any} scattering length however small and negative. Remarkably, the bound-state wave functions obtained for such configurations have nematic spin structure similar to those found in liquid He. Our results show that the BCS-BEC crossover is drastically affected by the presence of a non-Abelian gauge field. We discuss possible experimental signatures of our findings both at high and low temperatures.

6 pages, 3 figures; Minor error in section III(B) of the published version corrected; qualitative conclusions unaltered

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