2 research outputs found
Kondo regime in triangular arrangements of quantum dots: Molecular orbitals, interference and contact effects
Transport properties of an interacting triple quantum dot system coupled to
three leads in a triangular geometry has been studied in the Kondo regime.
Applying mean-field finite-U slave boson and embedded cluster approximations to
the calculation of transport properties unveils a set of rich features
associated to the high symmetry of this system. Results using both calculation
techniques yield excellent overall agreement and provide additional insights
into the physical behavior of this interesting geometry. In the case when just
two current leads are connected to the three-dot system, interference effects
between degenerate molecular orbitals are found to strongly affect the overall
conductance. An S=1 Kondo effect is also shown to appear for the perfect
equilateral triangle symmetry. The introduction of a third current lead results
in an `amplitude leakage' phenomenon, akin to that appearing in beam splitters,
which alters the interference effects and the overall conductance through the
system.Comment: 14 pages, 9 figures, submitted to PR
The tunnel magnetoresistance in chains of quantum dots weakly coupled to external leads
We analyze numerically the spin-dependent transport through coherent chains
of three coupled quantum dots weakly connected to external magnetic leads. In
particular, using the diagrammatic technique on the Keldysh contour, we
calculate the conductance, shot noise and tunnel magnetoresistance (TMR) in the
sequential and cotunneling regimes. We show that transport characteristics
greatly depend on the strength of the interdot Coulomb correlations, which
determines the spacial distribution of electron wave function in the chain.
When the correlations are relatively strong, depending on the transport regime,
we find both negative TMR as well as TMR enhanced above the Julliere value,
accompanied with negative differential conductance (NDC) and super-Poissonian
shot noise. This nontrivial behavior of tunnel magnetoresistance is associated
with selection rules that govern tunneling processes and various high-spin
states of the chain that are relevant for transport. For weak interdot
correlations, on the other hand, the TMR is always positive and not larger than
the Julliere TMR, although super-Poissonian shot noise and NDC can still be
observed