Nanomechanical Vibrations Research Articles

Time-averaged heat generation in a quantum dot driven by an alternating current bias

We theoretically study the time-averaged heat generation in a quantum dot over one period of an ac bias. By tuning the frequency ω of the ac bias, it is shown that for the definite ω=ωq/k, where ωq is the frequency of the phonon mode and k is an integer number, there appears an sharp resonant energy transfer from the electron subsystem to the phonon subsystem. Such a phenomenon can be interpreted as a consequence of the indirect coupling between the electric oscillation and the nanomechanical vibration via the tunnelling electrons. Moreover, this feature is susceptive to the parameters of transport, by change of which the heat generation will be limited or enhanced as we desire.

Mechano-electronic and electro-mechanical energy transfer in mesoscopic superconducting weak links

In this review we discuss how the nano-electro-mechanical properties of a superconducting weak link, formed by a suspended nanowire bridging two superconductors, can strongly affect mesoscopic effects in both the electronic and the mechanical subsystem. In particular we will discuss how quantum coherence and electron–electron (Coulomb) correlations may result in the possibility to resonantly redistribute energy between the electronic and mechanical degrees of freedom, allowing controllable switching between pumping and cooling of the nano-mechanical vibrations of the suspended nanowire. The two regimes of a given current and a given voltage supplied to the nano-electro-mechanical weak link is considered, resulting respectively in the possibility of ground-state cooling or resonant generation of nano-mechanical vibrations for realistic experimental parameters.

The Measurements of Nanomechanical Properties and Vibration Modal Analysis of Dragonfly Wing

The Measurements of Nanomechanical Properties and Vibration Modal Analysis of Dragonfly Wing

Individual transport of electrons through a chemisorbed Au nanodot in Coulomb blockade electron shuttles

The individual transport of electrons through a chemisorbed Au nanodot is observed in accordance with a nanomechanical vibration of the Au nanodot on a cantilever at 86 MHz; the experimental setup consists of a scanning tunneling microscopy probe/vacuum/chemisorbed Au nanodot/cantilever. In the tunneling current-distance characteristics, a constant current of ef [where f is an eigenfrequency of the cantilever (86 MHz)] is observed as a plateau over a distance of 0.35 nm; this plateau is five times wider than that observed in the case of physisorbed Au nanodots. Coulomb blockade electron shuttle devices with chemisorbed Au nanodots are one of the candidates for current standard devices.

Voltage-driven superconducting weak link as a refrigerator for cooling of nanomechanical vibrations

We consider a new type of cooling mechanism for a suspended nanowire acting as a weak link between two superconductive electrodes. By applying a bias voltage over the system, we show that the system can be viewed as a refrigerator for the nanomechanical vibrations, where energy is continuously transferred from the vibrational degrees of freedom to the extended quasiparticle states in the leads through the periodic modulation of the inter-Andreev level separation. The necessary coupling between the electronic and mechanical degrees of freedom responsible for this energy-transfer can be achieved both with an external magnetic or electrical field, and is shown to lead to an effective cooling of the vibrating nanowire. Using realistic parameters for a suspended nanowire in the form of a metallic carbon nanotube we analyze the evolution of the density matrix and demonstrate the possibility of cooling the system down to a stationary vibron population of ∼0.1. Furthermore, it is shown that the stationary occupancy of the vibrational modes of the nanowire can be directly probed using the dc current responsible for carrying away the absorbed energy from the vibrating nanowire.

Mechanical vibration-induced coherent optical spectroscopy in a single quantum dot coupled to a nanomechanical resonator

We theoretically propose a scheme to study coherent population oscillation (CPO) spectra in a system of a quantum dot coupled to a nanomechanical resonator. Due to nanomechanical vibrations CPO in a single quantum dot demonstrates novel features. In analogy with CPO in quantum optics, we refer to this effect as mechanically induced coherent population oscillation (MICPO). In this scheme, the vibration of the nanomechanical resonator makes a contribution to additional auxiliary energy levels so that the transparency phenomenon could be realized in such a system. The optical spectrum shows that the transparency based on MICPO can be controlled simply by the intensity of the optical field, the coupling strength and other relevant parameters. Furthermore, our technique provides detection in a real experiment to measure the decay rate of the nanomechanical resonator.

Cooling Torsional Nanomechanical Vibration by Spin-Orbit Interactions

We propose and study a spin-orbit interaction based mechanism to actively cool down the torsional vibration of a nanomechanical resonator made by semiconductor materials. We show that the spin-orbit interactions of electrons can induce a coherent coupling between the electron spins and the torsional modes of nanomechanical vibration. This coupling leads to an active cooling for the torsional modes through the dynamical thermalization of the resonator by the spin ensemble.

Superconducting pumping of nanomechanical vibrations

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.

Detection of nanomechanical vibrations by dynamic force microscopy in higher cantilever eigenmodes

The authors present a method based on dynamic force microscopy to characterize subnanometer-scale mechanical vibrations in resonant micro- and nanoelectromechanical systems. The method simultaneously employs the first eigenmode of the microscope cantilever for topography imaging and the second eigenmode for the detection of the resonator vibration. Here, they apply this scheme for the characterization of a 1.6GHz film bulk acoustic resonator, showing that it overcomes the main limitations of acoustic imaging in contact-mode atomic force microscopy. The method provides nanometer-scale lateral resolution on arbitrarily high resonant frequency systems, which makes it applicable to a wide diversity of electromechanical systems.

One by one single-electron transport in nanomechanical Coulomb blockade shuttle

Transport of electrons through a Au nanodot has been observed under a nanomechanical vibration of a Au nanodot on cantilever that consists of scanning tunneling microscopy probe/vacuum/Au nanodot/cantilever. In the probe tunneling current-distance characteristics, a constant probe current of 2ef has been observed as a plateau region, where f is an eigenfrequency of the cantilever of 86MHz. The authors discuss this quantized tunneling current in relation to one by one single-electron transport per cycle of operation in nanomechanical Coulomb blockade shuttle.

Spin-controlled nanoelectromechanics in magnetic NEM-SET systems

We present a theory of the nanoelectromechanical coupling in a magnetic nanoelectromechanical single-electron tunnelling (NEM-SET) device, where a nanometre-sized metallic cluster or ‘dot’ is suspended between two magnetic leads. In this device, the spin projections of the tunnelling electrons, which can be manipulated by an external magnetic field, control the strength of the tunnel current. The magnitude of the current, in turn, determines the power that can be supplied to the vibrational degree of freedom of the suspended cluster. The electromechanical instability that occurs in the system if the dissipation rate of the mechanical cluster vibration energy is slow enough, is shown to strongly depend on the external magnetic field. As a result different regimes of ‘shuttle’ vibrations appear and are analysed. The strength of the magnetic field required to control the nanomechanical vibrations decreases as the tunnel resistance of the device increases and can be as low as 10 gauss for gigaohm tunnel structures.

Observation of Coulomb staircases of both tunneling current and displacement current in nanomechanical double barrier tunneling structures

Displacement current staircase due to Coulomb blockade is observed together with a tunneling current staircase in nanomechanical double barrier tunneling structures that consist of scanning vibrating probe/colloidal Au particles/vacuum/PtPd substrate. We discuss the motion of single electrons on and through the Au particles from both the tunneling and displacement current staircases, and demonstrate the electron shuttle phenomenon due to nanomechanical probe vibration.