Abstract

Adiabatic transport (such as pumping) through a quantum dot reveals interesting properties due to quantum coherence and Coulomb interaction effects, which can not directly be found from a study of the time-independent system. In this seminar I want to discuss our latest studies of quantum dot systems subject to Coulomb interaction, modulated by time-dependent fields:

• The time-dependent non-linear transport current through an interacting quantum dot in the single-electron tunneling regime (SET) combines the study of pumping with the nonlinear bias regime. We propose an adiabatic transport spectroscopy where a ``time-averaged stability diagram’’ probes interactions, tunnel asymmetries and changes in the ground state spin-degeneracy.

• I will also present results on adiabatic pumping through a double dot coupled to normal metal or ferromagnetic contacts. Tunnel-induced renormalization effects due to charge fluctuations and tunneling through thermally excited states can play an important role here. In the presence of ferromagnetic leads, these effects can lead to an inverted spin-valve effect or even to a diverging tunneling magneto-resistance.

• Finally we compared the transient response of a quantum dot with strong Coulomb interaction to a fast change in the gate potential, to the stationary ac-response to a slow harmonic variation of the gate potential. The difference, not present in the classical case, arrises from higher-order tunneling processes.