Transmission Phase Shift of a Quantum Dot with Kondo Correlations (original) (raw)

Transmission Phase of a Singly Occupied Quantum Dot in the Kondo Regime

Physical Review Letters, 2008

We report on the phase measurements on a quantum dot containing a single electron in the Kondo regime. Transport takes place through a single orbital state. Although the conductance is far from the unitary limit, we measure for the first time, a transmission phase as theoretically predicted of π/2. As the dot's coupling to the leads is decreased, with the dot entering the Coulomb blockade regime, the phase reaches a value of π. Temperature shows little effect on the phase behaviour in the range 30-600 mK, even though both the two-terminal conductance and amplitude of the Aharonov-Bohm oscillations are strongly affected. These results confirm that previous phase measurements involved transport through more than a single level.

Quantum phase transition in a two-channel-Kondo quantum dot device

Physical Review B, 2004

We develop a theory of electron transport in a double quantum dot device recently proposed in Ref. 1 for the observation of the two-channel Kondo effect. Our theory provides a strategy for tuning the device to the non-Fermi-liquid fixed point, which is a quantum critical point in the space of device parameters. We explore the corresponding quantum phase transition, and make explicit predictions for behavior of the differential conductance in the vicinity of the quantum critical point.

Tunable Kondo screening in a quantum dot device

Physical Review B, 2005

We consider electron transport along a single-mode channel which is in contact, via tunnel junctions in its walls, with two quantum dots. Electron tunneling to and from the dots contributes to the electron backscattering, and thus modifies the channel conductance. If the dots carry spin, the channel conductance becomes temperature dependent due to the Kondo effect. The two-dot device geometry allows for a formation of S = 1 localized spin due to the indirect exchange interaction, called Ruderman-Kittel-Kasuya-Yosida interaction. This device offers a possibility to study the crossover between fully screened and under-screened Kondo impurity. We investigate the manifestation of such crossover in the channel conductance.

Orbital and spin Kondo effects in a double quantum dot

Europhysics Letters (EPL), 2001

Motivated by recent experiments, in which the Kondo effect has been observed for the first time in a double quantum-dot structure, we study electron transport through a system consisting of two ultrasmall, capacitively-coupled dots with large level spacing and charging energy. Due to strong interdot Coulomb correlations, the Kondo effect has two possible sources, the spin and orbital degeneracies, and it is maximized when both occur simultaneously. The large number of tunable parameters allows a range of manipulations of the Kondo physics-in particular, the Kondo effect in each dot is sensitive to changes in the state of the other dot. For a thorough account of the system dynamics, the linear and nonlinear conductance is calculated in perturbative and non-perturbative approaches. In addition, the temperature dependence of the resonant peak heights is evaluated in the framework of a renormalization group analysis.

Conductance of a spin-1 quantum dot: The two-stage Kondo effect

Physical Review B, 2007

We discuss the physics of a of a spin-1 quantum dot, coupled to two metallic leads and develop a simple model for the temperature dependence of its conductance. Such quantum dots are described by a two-channel Kondo model with asymmetric coupling constants and the spin screening of the dot by the leads is expected to proceed via a two-stage process. When the Kondo temperatures of each channel are widely separated, on cooling, the dot passes through a broad cross-over regime dominated by underscreened Kondo physics. A singular, or non-fermi liquid correction to the conductance develops in this regime. At the lowest temperatures, destructive interference between resonant scattering in both channels leads to the eventual suppression of the conductance of the dot. We develop a model to describe the growth, and ultimate suppression of the conductance in the two channel Kondo model as it is screened successively by its two channels. Our model is based upon large-N approximation in which the localized spin degrees of freedom are described using the Schwinger boson formalism.

Kondo Effect in a Few-Electron Quantum Ring

Physical Review Letters, 2003

A small quantum ring with less than 10 electrons was studied by transport spectroscopy. For strong coupling to the leads a Kondo effect is observed and used to characterize the spin structure of the system in a wide range of magnetic fields. At small magnetic fields Aharonov-Bohm oscillations influenced by Coulomb interaction appear. They exhibit phase jumps by π at the Coulomb-blockade resonances. Inside Coulomb-blockade valleys the Aharonov-Bohm oscillations can also be studied due to the finite conductance caused by the Kondo effect. Astonishingly, the maxima of the oscillations show linear shifts with increasing magnetic field and gate voltage.

Kondo effect in a side-coupled double-quantum-dot system embedded in a mesoscopic ring

Physical Review B Condensed Matter, 2009

We study finite-size effect of the Kondo screening cloud in a double quantum dot setup via a large-N slave-boson mean-field theory. In this setup, one of the dots is embedded in a close metallic ring with a finite size L and the other dot is side coupled to the embedded dot via an antiferromagnetic spin-spin-exchange coupling with a strength K. The antiferromagnetic coupling favors local spin-singlet state and suppresses the Kondo screening. The mean-field phase diagram as a function of 1 / L and K shows a crossover to the local spin-singlet ground state from the Kondo phase to occur at K Ͻ K c ͑L =4n ,4n +1,4n +3͒ and at K Ͼ K c ͑L =4n +2͒. The effective Kondo temperature T k ͑proptotional to inverse of the Kondo screening cloud size͒ shows the Kosterlitz-Thouless ͑KT͒ scaling at finite sizes for L =4n ,4n + 2, indicating quantum transition of the KT type between the Kondo screened phase for K Յ K c and a local spin-singlet phase for K Ն K c in the thermodynamic limit with K c being the critical value. The local density of states on the embedded quantum dot and the persistent current at finite sizes with different values of K are calculated in the crossover region.