We report on the generation of a quantum degenerate Fermi-Fermi mixture of two different atomic species. The quantum degenerate mixture is realized employing sympathetic cooling of fermionic Li-6 and K-40 gases by an evaporatively cooled bosonic Rb-87 gas. We describe the combination of trapping and cooling methods that proved crucial to successfully cool the mixture. In particular, we study the last part of the cooling process and show that the efficiency of sympathetic cooling of the Li-6 gas by Rb-87 is increased by the presence of K-40 through catalytic cooling. Due to the differing physical properties of the two components, the quantum degenerate Li-6 K-40 Fermi-Fermi mixture is an excellent candidate for a stable, heteronuclear system allowing to study several so far unexplored types of quantum matter.
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