65 research outputs found
Parity oscillations of Kondo temperature in a single molecule break junction
We study the Kondo temperature () of a single molecule break junction.
By employing a numerical renormalization group calculations we have found that
depends dramatically upon the position of the molecule in the wire formed
between the contacts. We show that exhibits strong \emph{oscillations}
when the parity of the left {and/or} right number of atomic sites ()
is changed. For a given set of parameters, the maximum value of occurs
for () combination, while its minimum values is observed for
().
These oscillations are fully understood in terms of the effective
hybridization function.Comment: 4 pages, 5 figure
Kondo screening suppression by spin-orbit interaction in quantum dots
We study the transport properties of a quantum dot embedded in an
Aharonov-Bohm ring in the presence of spin-orbit interactions. Using a
numerical renormalization group analysis of the system in the Kondo regime, we
find that the competition of Aharonov-Bohm and spin-orbit dynamical phases
induces a strong suppression of the Kondo state singlet, somewhat akin to an
effective intrinsic magnetic field in the system. This effective field breaks
the spin degeneracy of the localized state and produces a finite magnetic
moment in the dot. By introducing an {\em in-plane} Zeeman field we show that
the Kondo resonance can be fully restored, reestablishing the spin singlet and
a desired spin filtering behavior in the Kondo regime, which may result in full
spin polarization of the current through the ring.Comment: 4 pages, 4 figure
Capacitive interactions and Kondo effect tuning in double quantum impurity systems
We present a study of the correlated transport regimes of a double quantum
impurity system with mutual capacitive interactions. Such system can be
implemented by a double quantum dot arrangement or by a quantum dot and nearby
quantum point contact, with independently connected sets of metallic terminals.
Many--body spin correlations arising within each dot--lead subsystem give rise
to the Kondo effect under appropriate conditions. The otherwise independent
Kondo ground states may be modified by the capacitive coupling, decisively
modifying the ground state of the double quantum impurity system. We analyze
this coupled system through variational methods and the numerical
renormalization group technique. Our results reveal a strong dependence of the
coupled system ground state on the electron--hole asymmetries of the individual
subsystems, as well as on their hybridization strengths to the respective
reservoirs. The electrostatic repulsion produced by the capacitive coupling
produces an effective shift of the individual energy levels toward higher
energies, with a stronger effect on the `shallower' subsystem (that closer to
resonance with the Fermi level), potentially pushing it out of the Kondo regime
and dramatically changing the transport properties of the system. The effective
remote gating that this entails is found to depend nonlinearly on the
capacitive coupling strength, as well as on the independent subsystem levels.
The analysis we present here of this mutual interaction should be important to
fully characterize transport through such coupled systems.Comment: Submitted to Phys. Rev. B. 11 pages, 10 figure
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