Showing papers by "Yoseph Imry published in 2007"

Steps and dips in the ac conductance and noise of mesoscopic structures

Abstract: The frequency dependence of the equilibrium ac conductance (or the noise power spectrum) through a mesoscopic structure is shown to exhibit steps and dips. The steps, at energies related to the resonances of the structure, are closely related to the partial Friedel phases of these resonances, thus allowing a direct measurement of these phases (without interferometry). The dips in the spectrum are related to a destructive interference in the absorption of energy by transitions between these resonances, in some similarity with the Fano effect.

Minimal realization of the orbital Kondo effect in a quantum dot with two leads

Abstract: We demonstrate theoretically how the Kondo effect may be observed in the transport of spinless electrons through a quantum dot. The role of conduction-electron spin is played by a lead index. The Kondo effect takes place if there are two close levels in the dot populated by a single electron. For temperatures exceeding the Kondo temperature $T⪢{T}_{K}$, the conductance is maximal if the levels are exactly degenerate. However, at zero temperature, the conductance is zero at the SU(2) symmetric point but reaches the unitary limit $G={e}^{2}∕h$ for some finite value of the level splitting $\ensuremath{\Delta}\ensuremath{\epsilon}\ensuremath{\sim}{T}_{K}$. Introducing the spin $1∕2$ for electrons and having two degenerate orbital levels in the dot allows to observe the SU(4)-Kondo effect in a single dot coupled to two leads.

Level-occupation switching of the quantum dot, and phase anomalies in mesoscopic interferometry

Abstract: For a variety of quantum dots (QDs), the widths of different single-particle levels may naturally differ by orders of magnitude. In particular, the width of one strongly coupled level may be larger than the spacing between other, very narrow, levels. We found that in this case many consecutive Coulomb-blockade (CB) peaks are due to occupation of the same broad level. Between the peaks the electron jumps from this level to one of the narrow levels and the transmission through the dot at the next resonance essentially repeats that at the previous one. This offers a natural explanation of the salient features of the behaviour of the transmission phase in an interferometer with a QD. The theory of this effect will be reviewed with special emphasis on the role of the interactions. New results on the dot-charging measurements and the fine structure of occupation switchings will be presented, accompanied by the unified description of the whole series of CB peaks caused by single broad level. We then discuss the case where the system approaches the Kondo regime.

Level-occupation switching of the Quantum Dot, and phase anomalies in mesoscopic interferometry

Abstract: For a variety of quantum dots, the widths of different single-particle levels may naturally differ by orders of magnitude. In particular, the width of one strongly coupled level may be larger than the spacing between other, very narrow, levels. We found that in this case many consecutive Coulomb blockade peaks are due to occupation of the same broad level. Between the peaks the electron jumps from this level to one of the narrow levels and the transmission through the dot at the next resonance essentially repeats that at the previous one. This offers a natural explanation of the salient features of the behavior of the transmission phase in an interferometer with a QD. The theory of this effect will be reviewed with special emphasis on the role of the interactions. New results on the dot-charging measurements and the fine structure of occupation switchings will be presented, accompanied by the unified description of the whole series of CB peaks caused by a single broad level. We then discuss the case where the system approaches the Kondo regime.