Transmission Phase Shift of a Quantum Dot with Kondo Correlations

We use the Aharonov-Bohm effect in a four-terminal ring based on a Ga[Al]As heterostructure for the measurement of the relative transmission phase. In each of the two interfering paths we induce a quantum dot. The number of electrons in the two dots can be controlled independently. The transmission phase is measured as electrons are added to or taken away from the individual quantum dots.

Phase effects on the conductance of a double-dot system in a ring structure threaded by a magnetic flux are studied. The Aharonov-Bohm effect combined with the dot many-body charging effects determine the phases of the currents going through each arm of the ring. The cases for zero magnetic flux or half a quantum of flux are discussed in detail. It is shown that, depending upon the magnetic flux and the state of charge of the dots, controlled by gate potentials, the dephasing...

We demonstrate a tunable Kondo effect realized in small quantum dots. We can switch our dot from a Kondo impurity to a non-Kondo system as the number of electrons on the dot is changed from odd to even. We show that the Kondo temperature can be tuned by means of a gate voltage as a single-particle energy state nears the Fermi energy. Measurements of the temperature and magnetic field dependence of a Coulomb-blockaded dot show good agreement with predictions of both equilibriu...

The effect of electron-phonon coupling on transport through a pair of strongly correlated quantum dots embedded in the Aharonov-Bohm ring is considered in the mean field slave boson Kotliar-Ruckenstein approach. It is shown that coupling with phonons opens transport gap in the region of double occupancy. Low-bias conductance and thermopower provide information on electron-phonon coupling strength.

In this article, we review recent work about time dependent quantum transport through a quantum dot in Kondo regime. This represents a major step towards designing next generation transistors that are expected to replace current MOSFET's in a few years. We first discuss the effects of the density of states of gold contacts on the instantaneous conductance of an asymmetrically coupled quantum dot that is abruptly moved into Kondo regime via a gate voltage. Next, we investigate...

We consider the physics of transport through quantum dots in the presence of two tunneling paths. The first path sees electrons hopping on and off the dot while the second path is modeled through a potential scattering-like term. To study the effects of potential scattering, we employ a modified version of the Anderson model. Such a model can be exactly solved through the Bethe ansatz, thus allowing a comprehensive and exact analysis of the zero temperature linear response co...

A dilute concentration of magnetic impurities can dramatically affect the transport properties of an otherwise pure metal. This phenomenon, known as the Kondo effect, originates from the interactions of individual magnetic impurities with the conduction electrons. Nearly a decade ago, the Kondo effect was observed in a new system, in which the magnetic moment stems from a single unpaired spin in a lithographically defined quantum dot, or artificial atom. The discovery of the ...

We investigate the Fano-Kondo interplay in an Aharonov-Bohm ring with an embedded non-interacting quantum dot and a Coulomb interacting quantum dot. Using a slave-boson mean-field approximation we diagonalize the Hamiltonian via scattering matrix theory, and derive the conductance in the form of a Fano expression, which depends on the mean field parameters. We predict that in the Kondo regime the magnetic field leads to a gapped energy level spectrum due to hybridisation of t...

The transmission phase through a quantum dot with few electrons shows a complex, non-universal behavior. Here we combine configuration-interaction calculations ---treating rigorously Coulomb interaction--- and the Friedel sum rule to provide a rationale for the experimental findings. The phase evolution for more than two electrons is found to strongly depend on dot's shape and electron density, whereas from one to two the phase never lapses. In the Coulomb (Kondo) regime the ...

The Kondo effect is theoretically studied in a quantum dot embedded in a mesoscopic ring. The ring is connected to two external leads, which enables the transport measurement. Using the "poor man's" scaling method, we obtain analytical expressions of the Kondo temperature T_K as a function of the Aharonov-Bohm phase \phi by the magnetic flux penetrating the ring. In this Kondo problem, there are two characteristic lengths. One is the screening length of the charge fluctuation...