Cooling of nanomechanical vibrations by Andreev injection

TL;DR

This paper demonstrates that electron tunneling in a carbon nanotube-based nanoelectromechanical system can induce significant cooling of mechanical vibrations, with the effective temperature controllable via device parameters, and proposes using current measurements to observe this effect.

Contribution

It introduces a model where superconducting proximity effects influence nanotube vibrations, revealing a mechanism for cooling mechanical modes through Andreev injection.

Findings

Mechanical subsystem reaches a Boltzmann distribution with a tunable effective temperature.

Effective temperature can be significantly reduced, indicating cooling of vibrations.

Fluctuations in the nanotube strongly influence the dc current, enabling experimental probing.

Abstract

A nanoelectromechanical weak link composed of a carbon nanotube suspended between two normal electrodes in a gap between two superconducting leads is considered. The nanotube is treated as a movable single-level quantum dot in which the position-dependent superconducting order parameter is induced due to the Cooper pair tunneling. We show that electron tunneling processes significantly affect the state of the mechanical subsystem. We found that at a given direction of the applied voltage between the electrodes, the stationary state of the mechanical subsystem has a Boltzmann form with an effective temperature depended on the parameters of the device. As this takes place, the effective temperature can reach significantly small values (cooling effect). We also demonstrate that nanotube fluctuations strongly affect the dc current through the system. The latter can be used to probe the predicted effects in an experiment.