Exotic superfluidity in spin-orbit coupled Bose-Einstein condensates

We study the superfluidity of a spin-orbit coupled Bose-Einstein condensate (BEC) by computing its Bogoliubov excitations, which are found to have two branches: one is gapless and phonon-like at long wavelength; the other is typically gapped. These excitations imply superfluidity that has two new features: i) due to the absence of the Galilean invariance, one can no longer define the critical velocity of superfluidity independent of the reference frame; ii) the superfluidity depends not only on whether the speed of the BEC exceeds a critical value, but also on cross-helicity that is defined as the direction of the cross-product of the spin and the kinetic momentum of the BEC. Copyright (C) EPLA, 2012http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000315514100003&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701Physics, MultidisciplinarySCI(E)39ARTICLE5null10