  We show that the combination of a Dresselhaus interaction and a spatially
periodic Rashba interaction leads to the formation of a helical liquid in a
quantum wire when the electron-electron interaction is weakly screened. The
effect is sustained by a helicity-dependent effective band gap which depends on
the size of the Dresselhaus and Rashba spin-orbit couplings. We propose a
design for a semiconductor device in which the helical liquid can be realized
and probed experimentally.
