Quantum Shock Waves and Domain Walls in the Real-Time Dynamics of a   Superfluid Unitary Fermi Gas
  We show that in the collision of two superfluid fermionic atomic clouds one observes the formation of quantum shock waves as discontinuities in the number density and collective flow velocity. Domain walls, which are topological excitations of the superfluid order parameter, are also generated and exhibit abrupt phase changes by $\pi$ and slower motion than the shock waves. The domain walls are distinct from the gray soliton train or number density ripples formed in the wake of the shock waves and observed in the collisions of superfluid bosonic atomic clouds. Domain walls with opposite phase jumps appear to collide elastically. 
Aurel Bulgac, Yuan-Lung (Alan) Luo, and Kenneth J. Roche
cond-mat.quant-gas nucl-th quant-ph