  A nanoscale variable resistor consisting of a metal nanowire (active
element), a dielectric, and a gate, is proposed. By means of the gate voltage,
stochastic transitions between different conducting states of the nanowire can
be induced, with a switching time as fast as picoseconds. With an appropriate
choice of dielectric, the transconductance of the device, which may also be
considered an ``electromechanical transistor,'' is shown to significantly
exceed the conductance quantum G_0=2e^2/h, a remarkable figure of merit for a
nanoscale device.
