We study the effect of a local external potential on a system of two parallel
spin-polarized nanowires placed close to each other. For single channel
nanowires with repulsive interaction we find that transport properties of the
system are highly sensitive to the transverse gradient of the perturbation: the
asymmetric part completely reflects the electrons leading to vanishing
conductance at zero temperature, while the flat potential remains transparent.
We envisage a possible application of this unusual property in the sensitive
measurement of local potential field gradients.Comment: 4+ pages, 2 figures, typos correcte
