Double-degenerate Bose-Fermi mixture of strontium

Abstract

We report on the attainment of a spin-polarized Fermi sea of $^{87}\mathrm{Sr}$ in thermal contact with a Bose-Einstein condensate (BEC) of $^{84}\mathrm{Sr}$. Interisotope collisions thermalize the fermions with the bosons during evaporative cooling. A degeneracy with $T/{T}_{F}=0.30(5)$ is reached for a $^{87}\mathrm{Sr}$ Fermi sea of $2\ifmmode\times\else\texttimes\fi{}{10}^{4}$ atoms together with an almost pure $^{84}\mathrm{Sr}$ BEC of ${10}^{5}$ atoms.