  We propose several novel physical phenomena based on nano-scale helical
wires. Applying a static electric field transverse to the helical wire induces
a metal to insulator transition, with the band gap determined by the applied
voltage. Similar idea can be applied to "geometrically" constructing
one-dimensional systems with arbitrary external potential. With a quadrupolar
electrode configuration, the electric field could rotate in the transverse
plane, leading to a quantized dc charge current proportional to the frequency
of the rotation. Such a device could be used as a new standard for the high
precession measurement of the electric current. The inverse effect implies that
passing an electric current through a helical wire in the presence of a
transverse static electric field can lead to a mechanical rotation of the
helix. This effect can be used to construct nano-scale electro-mechanical
motors. Finally, our methodology also enables new ways of controlling and
measuring the electronic properties of helical biological molecules such as the
DNA.
