  Spin-momentum locking in a semiconductor device with strong spin-orbit
coupling (SOC) is a fundamental goal of nanoscale spintronics and an important
prerequisite for the formation of Majorana bound states. Such a helical state
is predicted in one-dimensional (1D) nanowires subject to strong Rashba SOC and
spin-mixing, its hallmark being a characteristic reentrant behaviour in the
conductance. Here, we report the first direct experimental observations of the
reentrant conductance feature, which reveals the formation of a helical liquid,
in the lowest 1D subband of an InAs nanowire. Surprisingly, the feature is very
prominent also in the absence of magnetic fields. This behaviour suggests that
exchange interaction exhibits substantial impact on transport in our device. We
attribute the opening of the pseudogap to spin-flipping two-particle
backscattering. The all-electric origin of the ideal helical transport bears
momentous implications for topological quantum computing.
