Spin-rotation coupling in p-wave Feshbach resonances

We report on the observation of spin-rotation coupling in p-wave Feshbachnresonances in an ultracold mixture of fermionic ⁶Li and bosonic ¹³³Cs. In addition to the doublet structure in the Feshbach spectrum due to spin-spin interaction, we observe a triplet structure of different ??_ℓ states by magnetic field dependent atom-loss spectroscopy. Here, the ??_ℓ states are projections of the pair-rotation angular momentum ℓ on the external magnetic field. Through comparison with coupled-channel calculations, we attribute the observed splitting of the ??_ℓ = ±1 components to electron spin-rotation coupling. Comparison with an oversimplified model, estimating the spin-rotation coupling by describing the weakly bound close channel molecular state with the perturbative multipole expansion, reveals the significant contribution of the molecular wavefunction at short internuclear distances. Our findings highlight the potential of Feshbach resonances in providing precise information on short- and intermediate-range molecular couplings and wavefunctions. We also present measurements of spin-spin coupling in p-wave Feshbach resonances in a Li⁶ mixture and three-body-losses in a non-thermalizing regime.