  We investigate the two-body properties of a spin-1/2 Fermi gas subject to a
spin-orbit coupling induced by laser fields. When an attractive s-wave
interaction between unlike spins is present, the system may form a dimer bound
state. Surprisingly, in the presence of a Zeeman field along the direction of
the spin-orbit coupling, the bound state obtains finite center-of-mass
mechanical momentum, whereas under the same condition but in the absence of the
two-body interaction, the system has zero total momentum. This unusual result
can be regarded as a consequence of the broken Galilean invariance by the
spin-orbit coupling. Such a finite-momentum bound state will have profound
effects on the many-body properties of the system.
