We consider a nanoelectromechanical Josephson junction, where a suspended nanowire serves as a superconducting weak link, and show that an applied dc bias voltage can result in suppression of the flexural vibrations of the wire. This cooling effect is achieved through the transfer of vibronic energy quanta first to voltage-driven Andreev states and then to extended quasiparticle electronic states. Our analysis, which is performed for a nanowire in the form of a metallic carbon nanotube and in the framework of the density matrix formalism, shows that such self-cooling is possible down to the ground state of the flexural vibration mode of the nanowire.

We demonstrate that a supercurrent can pump energy from a battery that provides a voltage bias into nanomechanical vibrations. Using a device containing a nanowire Josephson weak link as an example we show that a nonlinear coupling between the supercurrent and a static external magnetic field leads to a Lorentz force that excites bending vibrations of the wire at resonance conditions. We also demonstrate the possibility to achieve more than one regime of stationary nonlinear vibrations and how to detect them via the associated dc Josephson currents and we discuss possible applications of such a multistable nanoelectromechanical dynamics.PACS numbers: 74.45.+c, 74.50.+r, 74.78.Na, 75.47.De Coupling of electronic and mechanical degrees of freedom on the nanometer length scale is the basic phenomenon behind the functionality of nanoelectromechanical (NEM) systems. Such a coupling can be mediated either by electrical charges or currents. Single-electron tunneling (SET) devices with movable islands or gate electrodes employ Coulomb forces to achieve capacitive 1,2 and shuttle NEM coupling 3,4 , where the latter involves both capacitive forces and charge transfer. Devices containing current carrying parts, on the other hand, will achieve NEM coupling through magnetic-field induced Lorentz forces. Focusing on the latter mechanism, a simple estimate shows that for a gold nanowire suspended over a few micrometer long trench, the mechanical displacement due to typical currents of order 100 nA in magnetic fields of order 0.01 T can be as large as one nanometer. Such displacements can crucially affect the performance of mesoscopic devices.In this Letter we will explore a possible scenario for how highly nonlinear nanoelectromechanical effects can arise if the magnetic-field induced electromotive force caused by the mechanical motion of a conducting wire strongly perturbs the flow of current through it. Devices which contain superconductors, with their known extreme sensitivity to external electric fields, are the best candidates to achieve such strong effects and superconducting quantum interference devices (SQUID's) that incorporate a nanomechanical resonator are particularly interesting. Significant research has recently been performed in this direction (see e.g , by using a coupling between the SQUID dynamics and the resonator's mechanical vibrations due to the constraint set by the flux quantization phenomenon. Here we will consider the new possibility for NEM coupling that occurs if the nanomechanical element is an integral part of the superconducting weak link. In this case the NEM vibrations directly affect the Cooper pair tunneling and significantly modify the properties of the link. With a voltage biased weak link it becomes possible to pump nanomechanical vibrations in the Cooper pair tunneling region. As we will show below the result is a peculiar nonlinear NEM dynamics that affect both the supercurrent flow and the nanomechanical vibrations in novel ways. A nanowire is suspended between two superconducting el...

Strong coupling between electronic and mechanical degrees of freedom is a basic requirement for the operation of any nanoelectromechanical device. In this Review we consider such devices and in particular investigate the properties of small tunnel-junction nanostructures that contain a movable element in the form of a suspended nanowire. In these systems, electrical current and charge can be concentrated to small spatial volumes resulting in strong coupling between the mechanics and the charge transport. As a result, a variety of mesoscopic phenomena appear, which can be used for the transduction of electrical currents into mechanical operation. Here we will in particular consider nanoelectromechanical dynamics far from equilibrium and the effect of quantum coherence in both the electronic and mechanical degrees of freedom in the context of both normal and superconducting nanostructures.

We demonstrate that a suspended nanowire forming a weak link between two superconductors can be cooled to its motional ground state by a supercurrent flow. The predicted cooling mechanism has its origins in magnetic field induced inelastic tunneling of the macroscopic superconducting phase associated with the junction. Furthermore, we show that the voltage drop over the junction is proportional to the average population of the vibrational modes in the stationary regime, a phenomenon which can be used to probe the level of cooling.

We consider electronic transport through a suspended voltage-biased nanowire subject to an external magnetic field. In this paper, we show that the transverse magnetic field, which acts to induce coupling between the tunnelling current and the vibrational modes of the wire, controls the current-voltage characteristics of the system in novel ways. In particular, we derive the quantum master equation for the reduced density matrix describing the nanowire vibrations. From this we find a temperature-and bias voltage-independent current deficit in the limit of high bias voltage since the current through the device is lower than its value at zero magnetic field. We also find that the corrections to the current from the back-action of the vibrating wire decay exponentially in the limit of high voltage. Furthermore, it is shown that the expression for the temperature-and bias voltage-independent current deficit holds even if the nanowire vibrational modes have been driven out of thermal equilibrium.