17 research outputs found
Many-particle resonances in excited states of semiconductor quantum dots
Anderson impurity model for semiconductor quantum dot is extended to take
into account both particle and hole branches of charge excitations. It is shown
that in dots with even number of electrons where the Kondo effect is absent in
the ground state, novel midgap exciton states emerge in the energy spectrum due
to Kondo-type shake-up processes. The relevance of the model to
heterostructures doped by transition metal impurities and to rare earth ions
adsorbed on metallic surfaces is discussed.Comment: 9 pages, 6 ps figure
Dynamical and point symmetry of the Kondo effect in triangular quantum dot
In this work we concentrate on the {\it point symmetry} of triangular triple
quantum dot and its interplay with the {\it spin rotation symmetry} in the
context of Kondo tunneling through this kind of artificial molecule.
A fully symmetric triangular triple quantum dot is considered, consisting of
three identical puddles with the same individual properties (energy levels and
Coulomb blockade parameters) and inter-dot coupling (tunnel amplitudes and
electrostatic interaction). The underlying Kondo physics is determined by the
product of a discrete rotation symmetry group in real space and a continuous
rotation symmetry in spin space. These symmetries are reflected in the
resulting exchange hamiltonian which naturally involves spin and orbital
degrees of freedom. The ensuing poor-man scaling equations are solved and the
Kondo temperature is calculated.Comment: 7 pages 1 figure, to appear in the proceeding of FQMT04 (Prague, July
2004
Magnetic field induced two-channel Kondo effect in multiple quantum dots
We study the possibility to observe the two channel Kondo physics in multiple
quantum dot heterostructures in the presence of magnetic field. We show that a
fine tuning of the coupling parameters of the system and an external magnetic
field may stabilize the two channel Kondo critical point. We make predictions
for behavior of the scaling of the differential conductance in the vicinity of
the quantum critical point, as a function of magnetic field, temperature and
source-drain potential.Comment: 7 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-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
Cotunneling through quantum dot with even number of electrons
We study an influence of a finite magnetic field on a small spin-degenerate
quantum dot with even number of electrons, attached to metallic leads. It is
shown that, under certain conditions, the low energy physics of the system can
be described by the S=1/2 antiferromagnetic Kondo model.Comment: Contribution to LT-22; to be published in Physica