50 research outputs found
Spintromechanics of a Magnetic Nanoshuttle
We investigate theoretically the prospects for using a magnetic
nanoelectromechanical single-electron tunneling (NEM-SET) device as an
electronic spin filter. We find that strong magnetic exchange forces on the net
spin of the mobile central dot of the NEM-SET structure lead to spin-dependent
mechanical displacements ("spin polarons"), which give rise to vastly different
tunnelling probabilities for electrons of different spin. The resulting spin
polarization of the current can be controlled by bias and gate voltages and be
very close to 100% at voltages and temperatures below a characteristic
correlation energy set by the sum of the polaronic and Coulomb blockade
energies.Comment: Accepted for publication as a Rapid Communication in Phys. Rev. B and
selected as an "Editors' Suggestion" paper. This version has minor
modifications compared to arXiv:1205.2979, which it replace
Superconductive 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.Comment: 4 pages, 5 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
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
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
Nanomechanical manipulation of superconducting charge-qubit quantum networks
We suggest a nanoelectromechanical setup and corresponding time-protocol for
controlling parameters in order to demonstrate nanomechanical manipulation of
superconducting charge-qubit quantum network. We illustrate it on an example
reflecting important task for quantum information processing - transmission of
quantum information between two charge-qubits facilitated by nanomechanics. The
setup is based on terminals utilizing the AC Josephson effect between bias
voltage-controlled bulk superconductors and mechanically vibrating mesoscopic
superconducting grain in the regime of the Cooper pair box, controlled by the
gate voltage. The described manipulation of quantum network is achieved by
transduction of quantum information between charge-qubits and intentionally
built nanomechanical coherent states, which facilitate its transmission between
qubits. This performance is achieved using quantum entanglement between
electrical and mechanical states.Comment: 8 pages, 4 figure