Counter-flow instability of a quantum mixture of two superfluids Marta Abad, Alessio Recati, Sandro Stringari and Frédéric Chevy Eur. Phys. J. D, 69 5 (2015) 126 Published online: 13 May 2015 DOI: 10.1140/epjd/e2015-50851-y