  The superfluid mixture of interacting Bose and Fermi species is a remarkable
many-body quantum system. Dilute degenerate atomic gases, especially for two
species of distinct masses, are excellent candidates for exploring fundamental
features of superfluid mixture. However, producing a mass-imbalance Bose-Fermi
superfluid mixture, providing an unambiguous visual proof of two-species
superfluidity and probing inter-species interaction effects remain challenging.
Here, we report the realization of a two-species superfluid of lithium-6 and
potassium-41. By rotating the dilute gases, we observe the simultaneous
existence of vortex lattices in both species, and thus present a definitive
visual evidence for the simultaneous superfluidity of the two species.
Pronounced effects of the inter-species interaction are demonstrated through a
series of precision measurements on the formation and decay of two-species
vortices. Our system provides a new platform for studying novel macroscopic
quantum phenomena in vortex matter of interacting species.
