  We consider a nanoelectromechanical system composed of a carbon nanotube
suspended between two normal leads and coupled to a superconducting scanning
tunneling microscope (STM) tip via vacuum tunnel barrier. Treating the nanotube
as a single-level quantum dot, it is shown that an applied voltage between the
superconducting STM tip and normal leads gives rise to a pumping or a cooling
of the mechanical subsystem depending on the direction of the electronic flow.
It is also demonstrated that the transition between these two regimes is
controlled by the strength of the tunnel coupling between the nanotube and
superconducting STM tip and the relative position of the electronic level. Such
phenomena are realized due to a specific electromechanical coupling that is
fully governed by the quantum dynamics of the Cooper pairs. The amplitude of
the self-sustained oscillations in the pumping regime is analyzed numerically,
and the effective temperature of the mechanical subsystem in the cooling regime
is obtained.
