23 research outputs found
Negative tunnel magnetoresistance and differential conductance in transport through double quantum dots
Spin-dependent transport through two coupled single-level quantum dots weakly
connected to ferromagnetic leads with collinear magnetizations is considered
theoretically. Transport characteristics, including the current, linear and
nonlinear conductance, and tunnel magnetoresistance are calculated using the
real-time diagrammatic technique in the parallel, serial, and intermediate
geometries. The effects due to virtual tunneling processes between the two dots
via the leads, associated with off-diagonal coupling matrix elements, are also
considered. Negative differential conductance and negative tunnel
magnetoresistance have been found in the case of serial and intermediate
geometries, while no such behavior has been observed for double quantum dots
coupled in parallel. It is also shown that transport characteristics strongly
depend on the magnitude of the off-diagonal coupling matrix elements.Comment: 12 pages, 13 figure
Kondo-Dicke resonances in electronic transport through triple quantum dots
Electronic transport through a triple quantum dot system, with only a single
dot coupled directly to external leads, is considered theoretically. The model
includes Coulomb correlations in the central dot, while such correlations in
the two side-coupled dots are omitted. The infinite-U mean-field slave-boson
approach is used to obtain basic transport characteristics in the Kondo regime.
When tuning position of the side-coupled dots' levels, transition from
subradiant to superradiant like mode (and vice versa) has been found in the
spectral function, in analogy to the Dicke effect in atomic physics. Bias
dependence of the differential conductance and zero frequency shot noise is
also analysed.Comment: 8 pages, 10 figure