We report measurements of the Kondo effect in a double quantum dot, where the orbital states act as pseudospin states whose degeneracy contributes to Kondo screening. Standard transport spectroscopy as a function of the bias voltage on both dots shows a zero-bias peak in conductance, analogous to that observed for spin Kondo in single dots. Breaking the orbital degeneracy splits the Kondo resonance in the tunneling density of states above and below the Fermi energy of the leads, with the resonances having different pseudospin character. Using pseudospin-resolved spectroscopy, we demonstrate the pseudospin character by observing a Kondo peak at only one sign of the bias voltage. We show that even when the pseudospin states have very different tunnel rates to the leads, a Kondo temperature can be consistently defined for the double quantum dot system.

In this Letter we suggest a realization of the SU(N) Kondo effect, using quantum dots at strong magnetic field. We propose using edge states of the quantum Hall effect as pseudospin that interact with multiple quantum dots structures. In the suggested realization one can access each pseudospin separately and hence may perform a set of experiments that were impossible until now. We focus on the realization of SU(2) and SU(3) Kondo effects and find in the unitary limit a conductivity of 3/4 quantum conductance in the SU(3) case.

We introduce a rate formalism to treat classically forbidden electron transport through a quantum dot (cotunneling) in the presence of a coupled measurement device. We demonstrate this formalism for a toy model case of cotunneling through a single-level dot while being coupled to a strongly pinched-off quantum point contact (QPC). We find that the detector generates three types of back-action: the measurement collapses the coherent transport through the virtual state, but at the same time allows for QPC-assisted incoherent transport, and widens the dot level. Last, we obtain the measured cotunneling time from the cross correlation between dot and QPC currents.Comment: 15 pages, 9 figures, 1 appendix, published versio

We study the coherent properties of transmission through Kondo impurities, by considering an open Aharonov-Bohm ring with an embedded quantum dot. We develop a novel many-body scattering theory which enables us to calculate the conductance through the dot G d , the transmission phase shift ϕt, and the normalized visibility η, in terms of the single-particle T -matrix. For the singlechannel Kondo effect, we find at temperatures much below the Kondo temperature TK that ϕt = π/2 without any corrections up to order (T /TK) 2 . The visibility has the form η = 1−(πT /TK) 2 . For the non-Fermi liquid fixed point of the two channel Kondo, we find that ϕt = π/2 despite the fact that a scattering phase shift is not defined. The visibility is η = 1/2(1 + 4λ √ πT ) with λ ∼ 1/ √ TK, thus at zero temperature exactly half of the conductance is carried by single-particle processes, and coherent transmission may actually increase with temperature. We explain that the spin summation masks the inherent scattering phases of the dot, which can be accessed only via a spin-resolved experiment. In addition, we calculate the effect of magnetic field and channel anisotropy, and generalize to the k-channel Kondo case.

We study a model of two interacting levels that are attached to two electronic leads, where one of the levels is attached very weakly to the leads. We use rate equations to calculate the average current and the noise of electrons transmitted through the two levels. We show that the shot noise is enhanced because of the interactions and that the Fano factor depends on the properties of the couplings between the levels and the leads. We study both sequential tunneling and cotunneling processes and show that there is a range of parameters in which the cotunneling processes affect the noise significantly, even though most of the current is carried by sequential tunneling processes.