Two-photon photoassociation spectroscopy of the 2Σ+ YbLi molecular ground state

We report on measurements of the binding energies of several weakly bound vibrational states of the paramagnetic (YbLi)-Yb-174-Li-6 molecule in the electronic ground state using two-photon spectroscopy in an ultracold atomic mixture confined in an optical dipole trap. We theoretically analyze the experimental spectrum to obtain an accurate description of the long-range potential of the ground-state molecule. Based on the measured binding energies, we arrive at an improved value of the interspecies s-wave scattering length a(s0) = 30 a(0). Employing coherent two-photon spectroscopy we also observe the creation of dark atom-molecule superposition states in the heteronuclear Yb-Li system. This paper is an important step towards the efficient production of ultracold YbLi molecules via association from an ultracold atomic mixture.