Sympathetic cooling in an optically trapped mixture of alkali and   spin-singlet atoms
  We report on the realization of a stable mixture of ultracold lithium and ytterbium atoms confined in a far-off-resonance optical dipole trap. We observe sympathetic cooling of 6Li by 174Yb and extract the s-wave scattering length magnitude |a6Li-174Yb| = (13 \pm 3)a0 from the rate of inter-species thermalization. Using forced evaporative cooling of 174Yb, we achieve reduction of the 6Li temperature to below the Fermi temperature, purely through inter-species sympathetic cooling. 
Vladyslav V. Ivanov, Alexander Khramov, Anders H. Hansen, William H.   Dowd, Frank Muenchow, Alan O. Jamison, and Subhadeep ...
physics.atom-ph cond-mat.quant-gas