31 research outputs found
Selective nonresonant excitation of vibrational modes in suspended graphene via vibron-plasmon interaction
We theoretically study a doped graphene ribbon suspended over a trench and
subject to an ac-electrical field polarized perpendicularly to the graphene
plane. In such a system, the external ac-field is coupled to the relatively
slow mechanical vibrations via plasmonic oscillations in the isolated graphene
sheet. We show that the electrical field generates an effective pumping of the
mechanical modes. It is demonstrated that in the case of underdamped plasma
oscillation, a peculiar kind of geometrical resonance of the mechanical and
plasma oscillations appear. Namely the efficiency of pumping significantly
increases when the wave number of the mechanical mode is in close agreement
with the wave number of the plasma waves. The intensity of the pumping
increases with the wave number of the mode. This phenomenon allows selective
actuation of different mechanical modes although the driving field is
homogeneous
Quantum Theory of Magnetoelectromotive Instability in Nanoelectromechanical Systems with Positive Differential Conductance
We consider dc-electronic transport through a nanowire suspended between two normal-metal leads in the presence of an external magnetic field. We show the very mechanism through which such a system, whose stationary current-voltage characteristic is essentially characterized by positive differential conductance, becomes unstable with respect to an onset of self-excited oscillations in electrical transport and mechanical vibrations. The self-excitation mechanism is based on the correlation between the occupancy of the quantized spin-split electronic energy levels inside the nanowire and the velocity of the nanowire with the crucial influence of strong enough retardation effects in magnetomotive coupling coming from mechanical vibrations
Nonresonant high frequency excitation of mechanical vibrations in graphene based nanoresonator
We theoretically analyse the dynamics of a suspended graphene membrane which
is in tunnel contact with grounded metallic electrodes and subjected to
ac-electrostatic potential induced by a gate electrode. It is shown that for
such system the retardation effects in the electronic subsystem generate an
effective pumping for the relatively slow mechanical vibrations if the driving
frequency exceeds the inverse charge relax- ation time. Under this condition
there is a critical value of the driving voltage ampli- tude above which the
pumping overcomes the intrinsic damping of the mechanical resonator leading to
a mechanical instability. This nonresonant instability is saturated by
nonlinear damping and the system exhibits self-sustained oscillations of
relatively large amplitude.Comment: Major revisio
Ground-state cooling of a suspended nanowire through inelastic macroscopic quantum tunneling in a current-biased Josephson junction
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 the voltage-drop over the junction is
proportional to the average population of the vibrational modes in the
stationary regime, a phenomena which can be used to probe the level of cooling.Comment: 5 pages, 3 figure
Shuttle-promoted nano-mechanical current switch
We investigate electron shuttling in three-terminal nanoelectromechanocal
device built on a movable metallic rod oscillating between two drains. The
device shows a double-well shaped electromechanical potential tunable by a
source-drain bias voltage. Four stationary regimes controllable by the bias are
found for this device: (i) single stable fixed point, (ii) two stable fixed
points, (iii) two limiting cycles, and (iv) single limiting cycle. In the
presence of perpendicular magnetic field the Lorentz force makes possible
switching from one electromechanical state to another. The mechanism of tunable
transitions between various stable regimes based on the interplay between
voltage controlled electromechanical instability and magnetically controlled
switching is suggested. The switching phenomenon is implemented for achieving
both a reliable \emph{active} current switch and sensoring of small variations
of magnetic field.Comment: 11 pages, 4 figure
Self-excited Oscillations of Charge-Spin Accumulation Due to Single-electron Tunneling
We theoretically study electronic transport through a layer of quantum dots
connecting two metallic leads. By the inclusion of an inductor in series with
the junction, we show that steady electronic transport in such a system may be
unstable with respect to temporal oscillations caused by an interplay between
the Coulomb blockade of tunneling and spin accumulation in the dots. When this
instability occurs, a new stable regime is reached, where the average spin and
charge in the dots oscillate periodically in time. The frequency of these
oscillations is typically of the order of 1GHz for realistic values of the
junction parameters
Self-sustained oscillations in nanoelectromechanical systems induced by Kondo resonance
We investigate instability and dynamical properties of nanoelectromechanical
systems represented by a single-electron device containing movable quantum dot
attached to a vibrating cantilever via asymmetric tunnel contact. The Kondo
resonance in electron tunneling between source and shuttle facilitates
self-sustained oscillations originated from strong coupling of mechanical and
electronic/spin degrees of freedom. We analyze stability diagram for
two-channel Kondo shuttling regime due to limitations given by the
electromotive force acting on a moving shuttle and find that the saturation
amplitude of oscillation is associated with the retardation effect of
Kondo-cloud. The results shed light on possible ways of experimental
realization of dynamical probe for the Kondo-cloud by using high tunability of
mechanical dissipation as well as supersensitive detection of mechanical
displacement
Cooling of a suspended nanowire by an AC Josephson current flow
We consider a nanoelectromechanical Josephson junction, where a suspended
nanowire serves as a superconducting weak link, and show that an applied DC
bias voltage an 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 a level where the
average occupation number of the lowest flexural vibration mode of the nanowire
is .Comment: 4 pages, 3 figure
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
to cool the system down to a stationary vibron population of .
Furthermore, it is shown that the stationary occupancy of the vibrational modes
of the nanowire can be directly probed from the DC current responsible for
carrying away the absorbed energy from the vibrating nanowire.Comment: 10 pages, 4 figure