Non-Galilean response of Rashba-coupled Fermi gases

We consider the effect of a momentum kick on the ground state of a noninteracting two-dimensional Fermi gas subject to Rashba spin-orbit coupling. Although the total momentum is a constant of motion, the gas does not obey the rules of Galilean relativity. Upon imprinting a small overall velocity to the noninteracting gas, we find that the Fermi sea is deformed in a nontrivial way. We also consider a weakly repulsive Fermi gas and find, from its Hartree shift, that the total ground state of the system may change into a deformed, finite-momentum ground state as the repulsion is increased beyond a critical value, without the need for any external Zeeman fields. We also discuss possible experimental signatures of these effects. © 2013 American Physical Society.