273 research outputs found
The Interplay of Charge and Spin in Quantum Dots: The Ising Case
The physics of quantum dots is succinctly depicted by the {\it Universal
Hamiltonian}, where only zero mode interactions are included. In the case where
the latter involve charging and isotropic spin-exchange terms, this would lead
to a non-Abelian action. Here we address an Ising spin-exchange interaction,
which leads to an Abelian action. The analysis of this simplified yet
non-trivial model shed some light on a more general case of charge and spin
entanglement. We present a calculation of the tunneling density of states and
of the dynamic magnetic susceptibility. Our results are amenable to
experimental study and may allow for an experimental determination of the
exchange interaction strength.Comment: 11 pages, 7 figure
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
U(1) and SU(2) quantum dissipative systems: The Caldeira-Leggett vs. the Amegaokar-Eckern-Sch\"on approaches
There are two paradigmatic frameworks for treating quantum systems coupled to
a dissipative environment: the Caldeira-Leggett and the
Ambegaokar-Eckern-Sch\"on approaches. Here we recall the differences between
them, and explain the consequences when each is applied to a zero dimensional
spin (possessing an SU(2) symmetry) in a dissipative environment (a dissipative
quantum dot near or beyond the Stoner instability point).Comment: Contribution for Leonid Keldysh 85 Festschrif
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