We investigate theoretically the linear and nonlinear conductance through a nanostructure with two-fold degenerate single levels, corresponding to the transport through nanostructures such as a carbon nanotube, or double dot systems with capacitive interaction. It is shown that the presence of the interaction asymmetry between orbits/dots affects significantly the profile of the linear conductance at finite temperature, and, of the nonlinear conductance, particularly around half-filling, where the two-particle Kondo effect occurs. Within the range of experimentally feasible parameters, the SU(4) universal behavior is suggested, and comparison with relevant experiments is made.
We develop a method of theoretically investigating the charge, energy and heat transport in the presence of the charge Kondo correlations. The Coulomb blockade oscillations of heat conductance in the single electron transistor exhibiting the charge Kondo effects are investigated. We explore the Wiedemann Franz ratio in both charge-single channel and charge-two channel Kondo regime. The close connections of our findings with the recent experiments on multi-channel charge Kondo effects are discussed.
The observation of the Kondo effect in quantum dots has provided new opportunities to finally observe the controversial Kondo screening cloud. We study how screening cloud effects appear in the conductance through a quantum wire containing a quantum dot when the length of the wire is comparable to the size of the screening cloud.
We report on a comprehensive study of spin-1/2 Kondo effect in a strongly-coupled quantum dot realized in a high-quality InAs nanowire. The nanowire quantum dot is relatively symmetrically coupled to its two leads, so the Kondo effect reaches the Unitary limit. The measured Kondo conductance demonstrates scaling with temperature, Zeeman magnetic field, and out-of-equilibrium bias. The suppression of the Kondo conductance with magnetic field is much stronger than would be expected based on a g-factor extracted from Zeeman splitting of the Kondo peak. This may be related to strong spin-orbit cou…
Zero bias anomalies in topological nanowires have recently captured significant attention, as they are possible signatures of Majorana modes. Yet there are many other possible origins of zero bias peaks in nanowires, for example, weak localization, Andreev bound states, or the Kondo effect. Here, we discuss observations of differential conductance peaks at zero bias voltage in nonsuperconducting electronic transport through a 3D topological insulator nanowire. The zero bias conductance peaks show logarithmic temperature dependence and often linear splitting with magnetic fields, both of which …
We quantitatively describe the main features of the magnetically induced conductance modulation of a Kondo quantum dot -- or chessboard pattern -- in terms of a constant-interaction double quantum dot model. We show that the analogy with a double dot holds down to remarkably low magnetic fields. The analysis is extended by full 3D spin density functional calculations. Introducing an effective Kondo coupling parameter, the chessboard pattern is self-consistently computed as a function of magnetic field and electron number, which enables us to quantitatively explain our experimental data.
We study the scanning tunneling microscopy response for magnetic atoms on open and structured surfaces using Wilson's renormalization group. We observe Fano resonances associated with Kondo resonances and interference effects. For a magnetic atom in a quantum corral coupled to the confined surface states, and experimentally relevant parameters, we observe a large confinement induced effect not present in the experiments. These results suggest that the Kondo screening is dominated by the bulk electrons rather than the surface ones.
The Fano-Kondo effect in zero-bias conductance is investigated based on a theoretical model for the T-shaped quantum dot. The conductance as a function of the gate voltage is generally characterized by a Fano asymmetric parameter q. With varying temperature the conductance shows a crossover between the high and low temperature regions compared with the Kondo temperature T_K: two Fano asymmetric peaks at high temperatures and the Fano-Kondo plateau inside a Fano peak at low temperatures. Temperature dependence of conductance is calculated numerically by the Finite temperature density matrix ren…
The electrical conductance of atomic metal contacts represents a powerful tool to detect nanomagnetism. Conductance reflects magnetism through anomalies at zero bias -- generally with Fano lineshapes -- due to the Kondo screening of the magnetic impurity bridging the contact. A full atomic-level understanding of this nutshell many-body system is of the greatest importance, especially in view of our increasing need to control nanocurrents by means of magnetism. Disappointingly, zero bias conductance anomalies are not presently calculable from atomistic scratch. In this Letter we demonstrate a w…
We calculate the finite temperature linear DC conductance of a generic single-impurity Anderson model containing an arbitrary number of Fermi liquid leads, and apply the formalism to closed and open long Aharonov-Bohm-Kondo (ABK) rings. We show that, as with the short ABK ring, there is a contribution to the conductance from the connected 4-point Green's function of the conduction electrons. At sufficiently low temperatures this contribution can be eliminated, and the conductance can be expressed as a linear function of the T-matrix of the screening channel. For closed rings we show that at te…
A theory of thermal transport in a two-channel Kondo system, such as the one formed by a small quantum dot coupled to two leads and to a larger dot, is formulated. The interplay of the two screening constants allows an exploration of the Fermi liquid and non-Fermi liquid regimes. By using analytical, as well as numerical renormalization group methods, we study the temperature dependence of the thermal conductance and the Lorentz number. We find that in the low temperature limit, the Lorentz number attains its universal value, irrespective of the nature of the ground state.
Low temperature zero-bias conductance through two side-coupled quantum dots is investigated using Wilson's numerical renormalization group technique. A low-temperature phase diagram is computed. Near the particle-hole symmetric point localized electrons form a spin-singlet associated with weak conductance. For weak inter-dot coupling we find enhanced conductance due to the two-stage Kondo effect when two electrons occupy quantum dots. When quantum dots are populated with a single electron, the system enters Kondo regime with enhanced conductance. Analytical expressions for the width of the Kon…
We review mechanisms of low-temperature electronic transport through a quantum dot weakly coupled to two conducting leads. Transport in this case is dominated by electron-electron interaction. At temperatures moderately lower than the charging energy of the dot, the linear conductance is suppressed by the Coulomb blockade. Upon further lowering of the temperature, however, the conductance may start to increase again due to the Kondo effect. We concentrate on lateral quantum dot systems and discuss the conductance in a broad temperature range, which includes the Kondo regime.
At zero temperature, the Landauer formalism combined with static density functional theory is able to correctly reproduce the Kondo plateau in the conductance of the Anderson impurity model provided that an exchange-correlation potential is used which correctly exhibits steps at integer occupation. Here we extend this recent finding to multi-level quantum dots described by the constant-interaction model. We derive the exact exchange-correlation potential in this model for the isolated dot and deduce an accurate approximation for the case when the dot is weakly coupled to two leads. We show tha…
Experiments on quantum point contacts have highlighted an anomalous conductance plateau at $0.7 (2e^2/h)$, with features suggestive of the Kondo effect. Here we present an Anderson model for transport through a point contact which we analyze in the Kondo limit. Hybridization to the band increases abruptly with energy but decreases with valence, so that the background conductance and the Kondo temperature $T_K$ are dominated by different valence transitions. This accounts for the high residual conductance above $T_K$. A spin-polarized current is predicted for Zeeman splitting $g^* μ_B B > k_B T…
We analyze the equilibrium frequency-dependent spin current noise and spin conductance through a quantum dot in the local moment regime. Spin current correlations behave markedly differently from charge correlations. Equilibrium spin correlations are characterized by two universal scaling functions in the absence of an external field: one of them is related to charge correlations, while the other one describes cross-spin correlations. We characterize these functions using a combination of perturbative and non-perturbative methods. We find that at low temperatures spin cross-correlations are su…
We study the differential conductance in the Kondo regime of a quantum dot coupled to multiple leads. When the bias is applied symmetrically on two of the leads ($V$ and $-V$, as usual in experiments), while the others are grounded, the conductance through the biased leads always shows the expected enhancement at {\it zero} bias. However, under asymmetrically applied bias ($V$ and $λV$, with $λ>0$), a suppression - dip - appears in the differential conductance if the asymmetry coefficient $λ$ is beyond a given threshold $λ_0= \sqrt[3]{1+r}$ determined by the ratio $r$ of the dot-leads coupling…
We demonstrate that the external irradiation brings decoherence in the spin states of the quantum dot. This effect cuts off the Kondo anomaly in conductance even at zero temperature. We evaluate the dependence of the DC conductance in the Kondo regime on the power of irradiation, this dependence being determined by the decoherence.
We study the response of a two-channel Kondo quantum dot device proposed by Y. Oreg and D. Goldhaber-Gordon [Phys. Rev. Lett. {\bf 90}, 136602 (2003)] to a spin-bias applied across one of its channels formed by Fermi liquid reservoirs weakly coupled to a spin-1/2 quantum dot. When the temperature $T<T_K$, the Kondo temperature of the device, the spin conductance depends on the Kondo coupling of the dot spin to the other channel in an anomalous manner. For isotropic Kondo couplings to the two channels the spin conductance is quantized for $T\ll T_K$ characterizing the two-channel Kondo fixed po…
Friedel's sum rule provides an explicit expression for a conductance functional, $\mathcal{G}[n]$, valid for the single impurity Anderson model at zero temperature. The functional is special because it does not depend on the interaction strength $U$. As a consequence, the Landauer conductance for the Kohn-Sham (KS) particles of density functional theory (DFT) coincides with the true conductance of the interacting system. The argument breaks down at temperatures above the Kondo scale, near integer filling, $n_{\text{d}σ}\approx 1/2$ for spins $σ{=}\uparrow\downarrow$. Here, the true conductance…
We review the mechanisms of low-temperature electron transport across a quantum dot weakly coupled to two conducting leads. Conduction in this case is controlled by the interaction between electrons. At temperatures moderately lower than the single-electron charging energy of the dot, the linear conductance is suppressed by the Coulomb blockade. Upon further lowering of the temperature, however, the conductance may start to increase again due to the Kondo effect. This increase occurs only if the dot has a non-zero spin S. We concentrate on the simplest case of S=1/2, and discuss the conductanc…
We study the nonequilibrium transport through a quantum dot coupled to normal and superconducting leads. We use the modified second-order perturbation theory to calculate the differential conductance and the local density of states at the quantum dot. In the strong but finite Coulomb interaction regime, the differential conductance shows an anomalous peak not at a zero bias voltage but at a finite bias voltage. We also observe an additional Kondo resonance besides the normal one in the local density of states, where the former is caused by nonequilibrium Andreev tunneling via the normal Kondo …
We study two double dot systems, one with dots in parallel and one with dots in series, and argue they admit an exact solution via the Bethe ansatz. In the case of parallel dots we exploit the exact solution to extract the behavior of the linear response conductance. The linear response conductance of the parallel dot system possesses multiple Kondo effects, including a Kondo effect enhanced by a nonpertubative antiferromagnetic RKKY interaction, has conductance zeros in the mixed valence regime, and obeys a non-trivial form of the Friedel sum rule.
We clarify the difference between entangled and nonentangled two-reservoir mesoscopic Kondo systems and reveal the reason why theories using the Keldysh formalism, quantum Monte Carlo calculations, and the renormalization group approaches cannot explain the line shapes of tunneling conductance of mesoscopic Kondo systems measured by using a two-terminal setup but explain those of a three-terminal setup. We emphasize that the previous theories study a nonentangled system, while real two-reservoir mesoscopic Kondo systems are entangled systems in which two reservoirs are within the coherent regi…
We study resonant tunneling through an interacting quantum dot coupled to normal metallic and superconducting leads. We show that large Coulomb interaction gives rise to novel effects in Andreev transport. Adopting an exact relation for the Green's function, we find that at zero temperature, the linear response conductance is enhanced due to Kondo-Andreev resonance in the Kondo limit, while it is suppressed in the empty site limit. In the Coulomb blockaded region, on the other hand, the conductance is reduced more than the corresponding conductance with normal leads because large charging ener…
We investigate electron transport under the two impurity Kondo problem with the Aharonov--Bohm and Aharonov--Casher effects. These interference effects induce the Ising-coupled Ruderman--Kittel--Kasuya--Yosida (RKKY) interaction. We discuss the inter- and intra-site spin conductance as well as charge conductance in the Kondo and the mixed-valence regimes using the slave boson mean field approximation.
Quantum entanglement between an impurity spin and electrons nearby is a key property of the single-channel Kondo effects. We show that the entanglement can be detected by measuring electron conductance through a double quantum dot in an orbital Kondo regime. We derive a relation between the entanglement and the conductance, when the SU(2) spin symmetry of the regime is weakly broken. The relation reflects the universal form of many-body states near the Kondo fixed point. Using it, the spatial distribution of the entanglement, hence, the Kondo cloud, can be detected, with breaking the symmetry …
Encouraged by the recent real-time renormalization group results we carried out a detailed analysis of the nonequilibrium Kondo conductance observed in an InAs nanowire-based quantum dot and found them to be in excellent agreement. We show that in a wide range of bias the Kondo conductance zero-bias anomaly is scaled by the Kondo temperature to a universal lineshape predicted by the numerical study. The lineshape can be approximated by a phenomenological expression of a single argument $eV_{sd}=k_{\rm B}T_{\rm K}$. The knowledge of an analytical expression for the lineshape provides an alterna…
We have measured the differential conductances $G(V,T)$ in several Al/AlO$_{x}$/Sc planar tunnel junctions between 2 and 35 K. As the temperature decreases to $\sim$ 16 K, the zero-bias conductance $G(0,T)$ crosses over from a standard $-$ln$T$ dependence to a novel $- \sqrt{T}$ dependence. Correspondingly, the finite bias conductance $G(V,T)$ reveals a two-channel Kondo scaling behavior between $\sim$ 4 and 16 K. The observed two-channel Kondo physics is ascribed to originating from a few localized spin-$\frac12$ Sc atoms situated slightly inside the AlO$_x$/Sc interface.
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 ful…
We propose that two-channel orbital Kondo ``spin'' 1/2 conductance can be measured in a quantum dot at Coulomb Blockade with an odd number of electrons with contacts in a pillar configuration, if an orthogonal magnetic field induces an appropriate level crossing. At the zero-temperature strong coupling fixed point the conductance reaches the unitarity limit with a non-Fermi liquid sqrt(T)-law.
We study the Kondo effect in a single quantum dot system with two or three orbitals by using the Bethe-ansatz exact solution at zero temperature and the non-crossing approximation at finite temperatures. For the two-orbital Kondo effect, the conductance is shown to be constant at absolute zero in any magnetic fields, but decrease monotonically with increasing fields at finite temperatures. In the case with more orbitals, the conductance increases at absolute zero, while it features a maximum structure as a function of the magnetic field at finite temperatures. We discuss how these characterist…
We present a large-N theory for the differential conductance, dI/dV, in Kondo systems measured via scanning tunneling spectroscopy. We demonstrate that quantum interference between tunneling processes into the conduction band and into the magnetic f-electron states is crucial in determining the experimental Fano lineshape of dI/dV. This allows one to uniquely extract the Kondo coupling and the ratio of the tunneling amplitudes from the experimental dI/dV curve. Finally, we show that dI/dV directly reflects the strength of the antiferromagnetic interaction in Kondo lattice systems.
Tunnelling conductances observed for mesoscopic Kondo systems exhibit a zero-bias peak and two coherent side peaks. The former peak is usually understood as a Kondo effect and the latter side peak is recently clarified as the effect of inter-reservoir coherence. However, fitting the experimental $dI/dV$ line shapes, where $I$ and $V$ denote the current and bias voltage, respectively, has not been performed theoretically. Here, we fit the entire line shape range of the tunnelling conductance observed for a quantum dot, quantum point contact, and magnetized atom adsorbed on an insulating layer c…
We present results of resistance fluctuation spectroscopy on single crystals of the predicted Kondo topological insulator material SmB$_6$. Our measurements show that at low temperatures, transport in this system takes place only through surface states. The measured noise in this temperature range arises due to Universal Conductance Fluctuations whose statistics was found to be consistent with theoretical predictions for that of two-dimensional systems in the Symplectic symmetry class. At higher temperatures, we find signatures of glassy dynamics and establish that the measured noise is caused…
Spin and charge transport through a quantum dot coupled to external nonmagnetic leads is analyzed theoretically in terms of the non-equilibrium Green function formalism based on the equation of motion method. The dot is assumed to be subject to spin and charge bias, and the considerations are focused on the Kondo effect in spin and charge transport. It is shown that the differential spin conductance as a function of spin bias reveals a typical zero-bias Kondo anomaly which becomes split when either magnetic field or charge bias are applied. Significantly different behavior is found for mixed c…
Combining ab initio calculations and effective models derived from them, we discuss the electronic structure of oxygen doped gold chains when one Au atom is replaced by any transition-metal atom of the $3d$ series. The effect of O doping is to bring extended Au $5d_{xz}$ and $5d_{yz}$ states to the Fermi level, which together with the Au states of zero angular momentum projection, lead to three possible channels for the screening of the magnetism of the impurity. For most 3d impurities the expected physics is similar to that of the underscreened Kondo model, with singular Fermi liquid behavior…
We analyze the transport properties of a double quantum dot device in the side-coupled configuration. A small quantum dot (QD), having a single relevant electronic level, is coupled to source and drain electrodes. A larger QD, whose multilevel nature is considered, is tunnel-coupled to the small QD. A Fermi liquid analysis shows that the low temperature conductance of the device is determined by the total electronic occupation of the double QD. When the small dot is in the Kondo regime, an even number of electrons in the large dot leads to a conductance that reaches the unitary limit, while fo…
In this work,we study the Kondo effect of a quantum dot (QD) connected to leads and to a discrete set of one particle states provided by a quantum box represented by a quantum ring (QR) pierced by a magnetic flux side attached to the QD. The interplay between the bulk Kondo effect and the so called Kondo box regime is studied. In this system the QR energies can be continuously modified by the application of the magnetic field. The crossover between these two regimes is analyzed by changing the connection of the QD to the QR from the weak to the strong coupling regime. In the weak coupling regi…
We investigate tunneling through a short interacting wire. We identify two temperature regimes (a) $T_{Kondo}<T\le T^{wire}=\hbar v_F/k_Bd$ ($d$ is the length of the short wire) and (b) $T<T_{Kondo}\ll T^{wire}$. In the first regime the effective (renormalized) electron-electron interaction is smaller than the tunneling matrix element. This is the situation at finite temperature $T$ where the single particle spectrum of the wire is characterized by a multilevel "quantum dot" system with magnetic quantum number S=0 which is higher in energy than the SU(2) spin doublet $S=\pm1/2$. Due to the sin…
We report a strong Kondo effect (Kondo temperature ~ 4K) at high magnetic field in a selective area growth semiconductor quantum dot. The Kondo effect is ascribed to a singlet-triplet transition in the ground state of the dot. At the transition, the low-temperature conductance approaches the unitary limit. Away from the transition, for low bias voltages and temperatures, the conductance is sharply reduced. The observed behavior is compared to predictions for a two-stage Kondo effect in quantum dots coupled to single-channel leads.
The scaling properties of the conductance of a Kondo impurity connected to two leads that are in or out of equilibrium has been extensively studied, both experimentally and theoretically. From these studies, a consensus has emerged regarding the analytic expression of the scaling function. The question addressed in this brief report concerns the properties of the experimentally measurable coefficient $α$ present in the term describing the leading dependence of the conductance on $eV/T_K$, where $V$ is the source-drain voltage and $T_K$ the Kondo temperature. We study the dependence of $α$ on t…
Determination of the molecular Kondo temperature $T_K$ poses a challenge in most cases when the experimental temperature cannot be tuned to a sufficient extent. We show how this ambiguity can be resolved if additional control parameters are present, such as magnetic field and mechanical gating. We record the evolution of the differential conductance by lifting an individual molecule from the metal surface with the tip of a scanning tunneling microscope. By fitting the measured conductance spectra with the single impurity Anderson model we are able to demonstrate that the lifting tunes the junc…
The conductance through a serial double dot structure for which the inter-dot tunneling is stronger than the tunneling to the leads is studied using the numerical density matrix renormalization group method and analytic arguments. When the dots are occupied by 1 or 3 electrons the usual Kondo peak is obtained. For the case in which 2 electrons occupy the molecule a singlet is formed. Nevertheless, the conductance in that case has a constant non-zero value, and might even be equal to the maximum conductance of $2 e^2/h$ for certain values of the molecule parameters. We show that this is the res…
A low-temperature scanning tunneling microscope is employed to build a junction comprising a Co atom bridging a copper-coated tip and a Cu(100) surface. An Abrikosov-Suhl-Kondo resonance is evidenced in the differential conductance and its width is shown to vary exponentially with the ballistic conductance regardless of the tip structure. Using a theoretical description based on the Anderson model, we show that the Kondo effect and the conductance are related through the atomic relaxations affecting the environment of the Co atom.
Motivated by recent experiments, we consider a single-electron transistor in the Kondo regime which is coupled to three leads in the presence of large bias voltages. Such a steady-state non-equilibrium system is to a large extent governed by a decoherence rate induced by the current through the dot. As the two-terminal conductance turns out to be rather insensitive to the decoherence rate, we study the conductance in a three-terminal device using perturbative renormalization group and calculate the characteristic splitting of the Kondo resonance. The interplay between potential biases and anis…
By introducing a normal self-energy to incorporate the effects of magnetic impurities, Kondo effects in single-walled metallic carbon nanotubes are investigated within the Anderson model and Landauer formula. Magnetic impurities induce Kondo resonance and bring a valley of conductance unction near the Fermi level. The conductance of the nanotube increases with the temperature in the low temperature range. Thermoelectric power induced by magnetic impurities is gotten from Mott relation, and the calculations indicate its dependence on the temperature could interpret the experiment well.
We study finite-frequency transport properties of the double-dot system recently constructed to observe the two-channel Kondo effect [R. M. Potok et al., Nature 446, 167 (2007)]. We derive an analytical expression for the frequency-dependent linear conductance of this device in the Kondo regime. We show how the features characteristic of the 2-channel Kondo quantum critical point emerge in this quantity, which we compute using the results of conformal field theory as well as numerical renormalization group methods. We determine the universal cross-over functions describing non-Fermi liquid vs.…
We develop the theory of conductance of a quantum dot which carries a spin and is coupled via RKKY interaction to another spin-carrying quantum dot. The found dependence of the differential conductance on bias and magnetic field at fixed RKKY interaction strength may allow one to distinguish between the possible ground states of the system. Transitions between the ground states are achieved by tuning the RKKY interaction, and the nature of these transitions can be extracted from the temperature dependence of the linear conductance. The feasibility of the corresponding measurements is evidenced…
Electron transport through a strongly correlated quantum dot (QD) embedded in an Aharonov-Bohm (AB) ring is investigated with the aid of the finite-U slave-boson mean-field (SBMF) approach extended to nonequilibrium regime. A nonequilibrium steady state (NESS) of the mean-field Hamiltonian is constructed with the aid of the C*-algebraic approach for studying infinitely extended systems. In the linear response regime, the Fano-Kondo resonances and AB oscillations of the conductance obtained from the SBMF approach are in good agreement with those from the numerical renormalization group techniqu…
Using exact-diagonalization of small clusters and Dyson equation embedding techniques, the conductance $G$ of linear arrays of quantum dots is investigated. The Hubbard interaction induces Kondo peaks at low temperatures for an odd number of dots. Remarkably, the Kondo peak is split in half by a deep minimum, and the conductance vanishes at one value of the gate voltage. Tentative explanations for this unusual effect are proposed, including an interference process between two channels contributing to $G$, with one more and one less particle than the exactly-solved cluster ground-state. The Hub…
We investigate the nonequilibrum transport properties of a quantum dot when spin flip processes compete with the formation of a Kondo resonance in the presence of ferromagnetic leads. Based upon the Anderson Hamiltonian in the strongly interacting limit, we predict a splitting of the differential conductance when the spin flip scattering amplitude is of the order of the Kondo temperature. We discuss how the relative orientation of the lead magnetizations strongly influences the electronic current and the shot noise in a nontrivial way. Furthermore, we find that the zero-bias tunneling magnetor…
We study the conductance of an electron interferometer formed in a two dimensional electron gas between a nanostructured quantum contact and the charged tip of a scanning gate microscope. Measuring the conductance as a function of the tip position, thermally induced rings may be observed in addition to Fabry-Pérot interference fringes spaced by half the Fermi wavelength. If the contact is made of a quantum dot opened in the middle of a Kondo valley, we show how the location of the rings allows to measure by electron interferometry the magnetic moment of the dot above the Kondo temperature.
We study a quantum dot connected to the bulk by single-mode junctions at almost perfect conductance. Although the average charge $e\langle N \rangle$ of the dot is not discrete, its spin remains quantized: $s=1/2$ or $s=0$, depending (periodically) on the gate voltage. This drastic difference from the conventional mixed-valence regime stems from the existence of a broad-band, dense spectrum of discrete levels in the dot. In the doublet state, the Kondo effect develops at low temperatures. We find the Kondo temperature $T_K$ and the conductance at $T\lesssim T_K$.
We systematically investigate electron transport through double quantum dots with particular emphasis on interference induced via multiple paths of electron propagation. By means of the slave-boson mean-field approximation, we calculate the conductance, the local density of states, the transmission probability in the Kondo regime at zero temperature. It is clarified how the Kondo-assisted transport changes its properties when the system is continuously changed among the serial, parallel and T-shaped double dots. The obtained results for the conductance are explained in terms of the Kondo reson…
We investigate a lateral semiconductor quantum dot with a large number of electrons in the limit of strong coupling to the leads. A Kondo effect is observed and can be tuned in a perpendicular magnetic field. This Kondo effect does not exhibit Zeeman splitting. It shows a modulation with the periodicity of one flux quantum per dot area at low temperatures. The modulation leads to a novel, strikingly regular stripe pattern for a wide range in magnetic field and number of electrons.
Equilibrium transport properties of a single-level quantum dot tunnel-coupled to ferromagnetic leads and exchange-coupled to a side nonmagnetic reservoir are analyzed theoretically in the Kondo regime. The equilibrium spectral functions and conductance through the dot are calculated using the numerical renormalization group (NRG) method. It is shown that in the antiparallel magnetic configuration, the system undergoes a quantum phase transition with increasing exchange coupling $J$, where the conductance drops from its maximum value to zero. In the parallel configuration, on the other hand, th…
Properties of the Kondo effect in quantum dots depend sensitively on the coupling parameters and so on the realization of the quantum dot -- the Kondo temperature itself becomes a mesoscopic quantity. Assuming chaotic dynamics in the dot, we use random matrix theory to calculate the distribution of both the Kondo temperature and the conductance in the Coulomb blockade regime. We study two experimentally relevant cases: leads with single channels and leads with many channels. In the single-channel case, the distribution of the conductance is very wide as $T_K$ fluctuates on a logarithmic scale.…
We employ the time-dependent non-crossing approximation to study the time averaged conductance for a single electron transistor in the Kondo regime when the dot level is sinusoidally driven from its equilibrium position by means of a gate voltage in finite bias. We find that the average conductance exhibits significant deviation from the monotonous reduction when the applied bias is equal to the driving frequency of the dot level. We investigate the effect of the temperature and the driving frequency on the observed enhancement. We attribute this behaviour to the overlap of the satellite Kondo…
Using the transversal vibration resonance of a suspended carbon nanotube as charge detector for its embedded quantum dot, we investigate the case of strong Kondo correlations between a quantum dot and its leads. We demonstrate that even when large Kondo conductance is carried at odd electron number, the charging behaviour remains similar between odd and even quantum dot occupation. While the Kondo conductance is caused by higher order processes, a sequential tunneling only model can describe the time-averaged charge. The gate potentials of maximum current and fastest charge increase display a …
