文摘
We investigate the formation of rashbon bound states and strong-coupling effects in an ultracold Fermi gas with a spherical spin–orbit interaction, \(H_\mathrm{so}=\lambda {\varvec{p}}\cdot \mathbf{\sigma }\) (where \(\mathbf{\sigma }=(\sigma _x,\sigma _y,\sigma _z)\) are Pauli matrices). Extending the strong-coupling theory developed by Nozières and Schmitt-Rink (NSR) to include this spin–orbit coupling, we determine the superfluid phase transition temperature \(T_\mathrm{c}\), as functions of the strength of a pairing interaction \(U_s\), as well as the spin–orbit coupling strength \(\lambda \). Evaluating poles of the NSR particle–particle scattering matrix describing fluctuations in the Cooper channel, we clarify the region where rashbon bound states dominate the superfluid phase transition in the \(U_s\)–\(\lambda \) phase diagram. Since the antisymmetric spin–orbit interaction \(H_\mathrm{so}\) breaks the inversion symmetry of the system, rashbon bound states naturally have not only a spin-singlet and even-parity symmetry, but also a spin-triplet and odd-parity symmetry. Thus, our results would be also useful for the study of this parity-mixing effect in the BCS–BEC crossover regime of a spin–orbit coupled Fermi gas.