Orbital Kondo effect in double quantum dots

Orbital Kondo effect in a system of two single-level quantum dots attached to external electron reservoirs is considered theoretically. The dots are coupled via direct hoping term and Coulomb interaction. The Kondo temperature is evaluated from the scaling approach and slave boson technique. The later method is also used to calculate linear conductance of the system. Nonlinear conductance, in turn, is calculated in terms of the nonequilibrium Green function formalism.Comment: 10 pages, 9 figures, revise

Beating in electronic transport through quantum dot based devices

Electronic transport through a two-level system driven by external electric field and coupled to (magnetic or non-magnetic) electron reservoirs is considered theoretically. The basic transport characteristics such as current and tunnel magnetoresistance (TMR) are calculated in the weak coupling approximation by the use of rate equation connected with Green function formalism and slave-boson approach. The time dependent phenomenon is considered in the gradient expansion approximation. The results show that coherent beats pattern can be observed both in current and TMR. The proposed system consisting of two quantum dots attached to external leads, in which the dots' levels can be tuned independently, can be realized experimentally to test this well known physical phenomenon. Finally, we also indicate possible practical applications of such device.Comment: 9 pages, 9 figure

Bohater literatury popularnej w ponowoczesnym świecie

Problematyka bohatera w literaturze popularnej, wbrew pozorom, jest skomplikowanym zagadnieniem. Przy czym, ze względu na specyfikę samej literatury i kultury popularnej oraz jej związkom z kulturą w szerokim rozumieniu tego pojęcia jest ciągle problemem żywym i ewoluującym. Z tego tez powodu nastręcza nie tylko kłopoty natury metodologicznej, ale stwarza także ciągle nowe perspektywy, których często brakuje w modelach kulturowych, która historycznie zakończyły swój naturalny bieg i stały się tylko przedmiotem badań. Pomimo, że przedmiotem refleksji jest bohater literatury popularnej w czasie płynnej ponowoczesności, to opisanie tego zjawiska wymaga szerszej perspektywy czasowej, dzięki której będzie można zrozumieć mechanizmy rządzące współczesną kreacją herosa obecnego w tym typie literatury

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