We characterize Feshbach resonances in all isotopologues of the $\mathrm{ Li}{ -}\mathrm{ Li}$ system with improved interaction potentials. Starting from spectroscopically accurate Morse/long-range (MLR) potential-energy curves for the singlet ($X^{ 1}\Sigma^{ +}$) and triplet ($a^{ 3}\Sigma^{ +}$) electronic states of $\mathrm{ Li}_2$, we apply small phenomenological inner-wall adjustments (following Julienne and Hutson, Phys. Rev. A 89, 052715 (2014), arXiv:1404.2623v3) and fit the resulting potentials to threshold measurements for the $^{ 6}\mathrm{ Li}{ -}^{ 6}\mathrm{ Li}$ and $^{ 7}\mathrm{ Li}{ -}^{ 7}\mathrm{ Li}$ isotopologues, including binding energies, scattering lengths, and Feshbach resonance positions. Using the optimized potentials in coupled-channels scattering calculations, we predict and characterize s-wave Feshbach resonances in the $^{ 6}\mathrm{ Li}{ -}^{ 7}\mathrm{ Li}$ isotopologue. In its lowest-energy hyperfine channel, all resonances are narrow ($\sim 0.01{ -}0.1$ G), strongly closed-channel dominated, and predominantly triplet in electronic spin character, in marked contrast to the homonuclear systems. These results provide a foundation for designing Raman optical-transfer pathways to produce ultracold $\mathrm{ Li}_2$ molecules in deeply bound rovibrational levels of both the $X^1\Sigma^{ +}$ and $a^3\Sigma^{ +}$ potentials across all three isotopologues.
Categories: physics.atom-ph cond-mat.quant-gas