Pumping and cooling of nanomechanical vibrations generated by Cooper pair exchange

TL;DR

This paper investigates how a superconducting STM tip can induce either pumping or cooling of a carbon nanotube's vibrations through quantum Cooper pair dynamics, depending on electronic flow and coupling parameters.

Contribution

It introduces a model for electromechanical coupling in a nanoelectromechanical system driven by superconducting Cooper pairs, revealing control over mechanical vibrations.

Findings

Voltage induces pumping or cooling depending on flow direction.

Transition controlled by tunnel coupling strength and electronic level position.

Self-sustained oscillations and effective temperature are numerically analyzed.

Abstract

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.