Exploring an Ultracold Fermi-Fermi Mixture: Interspecies Feshbach Resonances and Scattering Properties of ${}^6\mathrm{Li}$ and ${}^{40}\mathrm{K}$

We report on the observation of Feshbach resonances in an ultracold mixture of two fermionic species, ${}^6\mathrm{Li}$ and ${}^{40}\mathrm{K}$. The experimental data are interpreted using a simple asymptotic bound state model and full coupled channels calculations. This unambiguously assigns the observed resonances in terms of various $s$- and $p$-wave molecular states and fully characterizes the ground-state scattering properties in any combination of spin states.

Figure 1

Ground-state energies of ${}^6\mathrm{Li}$ and ${}^{40}\mathrm{K}$ versus magnetic field.

Figure 2

Feshbach scan of the $\mathrm{Li}|1⟩\mathrm{K}|2⟩$ mixture. The remaining fraction of ${}^{40}\mathrm{K}$ atoms relative to off-resonant regions after 10 s interaction with ${}^6\mathrm{Li}$ atoms is shown as a function of magnetic field. Loss features A, B, C, D, and F are due to interspecies Feshbach resonances. Loss feature E is caused by a ${}^{40}\mathrm{K}$ $p$-wave Feshbach resonance [19].

Figure 3

Bound state energies versus magnetic field. Dotted (dashed) lines indicate the $s$-wave ($p$-wave) states. The two-body threshold for the $\mathrm{Li}|1⟩\mathrm{K}|2⟩$ collision channel ($M_{\mathrm{F}}=-3$) is indicated by the solid line. The dots and the corresponding arrows indicate the measured resonance positions (see Fig. 2).

Figure 4

Results from coupled channels calculations for the magnetic-field dependence of the $s$-wave scattering length $a_s(B)$ (upper panel) and the $m_l=0$ contribution to the $p$-wave elastic scattering cross section ${\sigma }_p(E)$ for $E/k_B=12\mu \mathrm{K}$ (lower panel) for the channels in Table  with $M_{\mathrm{F}}=-4$ (solid line), $-3$ (dashed line), and $-2$ (dotted line). The dots indicate the measured resonance locations.