Spinor Bose-Einstein condensate flow past an obstacle
  We study the flow of a spinor (F=1) Bose-Einstein condensate in the presence of an obstacle. We consider the cases of ferromagnetic and polar spin-dependent interactions and find that the system demonstrates two speeds of sound that are identified analytically. Numerical simulations reveal the nucleation of macroscopic nonlinear structures, such as dark solitons and vortex-antivortex pairs, as well as vortex rings in one- and higher-dimensional settings respectively, when a localized defect (e.g., a blue-detuned laser beam) is dragged through the spinor condensate at a speed larger than the second critical speed. 
A. S. Rodrigues (1), P. G. Kevrekidis (2), R. Carretero-Gonz\'alez   (3), D. J. Frantzeskakis (4), P. Schmelcher (5), T. J. ...