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TU Dresden » Faculty of Mechanical Science and Engineering » Institute for Materials Science » Chair of Materials Science and Nanotechnology

Thursday, 03 July 2008
(at 13:00 in room 115, Hallwachsstr. 3)
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Driven transport through nanoscale conductors

Sigmund Kohler

Theoretical Physics I
Universität Augsburg

Electromagnetic ac fields can alter significantly the transport properties of mesoscopic systems like molecular wires and coherently coupled quantum dots. Resonant excitations of electrons e.g. enhance drastically the time-averaged currents. These systems may also be used to study the so-called ratchet or pump effect: in asymmetric molecules, an ac field induces a dc current even in the absence of any bias voltage. Of particular interest is the fact that the ratchet current as a function of the wire length converges to a non-zero value. The opposite phenomenon also exists: a proper off-resonant driving field reduces the coherent transport resulting in a strong current suppression. Most of these effects require a treatment beyond linear response theory. The corresponding transport mechanisms leave their fingerprints also in the noise whose relative strength is measured by the so-called Fano factor. In general, we find that resonant excitations reduce the noise level while current suppressions are accompanied by a noise reduction. In our studies, we model the external field by a periodic time-dependence of the wire Hamiltonian. This requires a generalization of established transport theories like, e.g., the Landauer formula. Such a generalization, that is based on the Floquet theorem and includes the full nonlinear response to the driving, will be presented and the main differences to the static situation will be discussed. Finally, we discuss how strong Coulomb repulsion modifies our results.

slides (pdf)

Invited by G. Cuniberti (nanoSeminar)

last modified: 2021.10.21 Thu
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