Signatures of electron correlations in the transport properties of quantum dots (original) (raw)
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Transport properties of quantum dots
Annalen der Physik, 2010
Linear and nonlinear transport through a quantum dot that is weakly coupled to ideal quantum leads is investigated in the parameter regime where charging and geometrical quantization effects coexist. The exact eigenstates and spins of a finite number of correlated electrons confined within the dot are combined with a rate equation. The current is calculated in the regime of sequential tunneling. The analytic solution for an Anderson impurity is given. The phenomenological charging model is compared with the quantum mechanical model for interacting electrons. The current-voltage characteristics show Coulomb blockade. The excited states lead to additional finestructure in the current voltage characteristics. Asymmetry in the coupling between the quantum dot and the leads causes asymmetry in the conductance peaks which is reversed with the bias voltage. The spin selection rules can cause a 'spin blockade' which decreases the current when certain excited states become involved in the transport. In two-dimensional dots, peaks in the linear conductance can be suppressed at low temperatures, when the total spins of the corresponding ground states differ by more than 1/2. In a magnetic field, an electron number parity effect due to the different spins of the many-electron ground states is predicted in addition to the vanishing of the spin blockade effect. All of the predicted features are consistent with recent experiments. electron tunneling (SET) transistors . In SET-devices, a controlled transfer of electrons -one by one -can be achieved [5] by applying . This could also open the way to a new current standard based on counting the electrons that pass the device per unit of time .
Quantum Theory of Electron Transport Through Single-Level Quantum Dot
2005
A new approach in the quantum theory of few-electron nanoelectronic devices-the S-matrix approach-is presented in a simple example: a single-electron transistor consisting of a single-level quantum dot connected with two metallic leads through the corresponding potential barriers. The electron transport through the quantum dot due to the electron tunneling between the dot and the leads is studied. The strong Coulomb repulsion between the electrons in the dot is taken into account exactly, while the tunneling between the dot and the leads, considered as a small perturbation, is studied by means of the perturbation theory. For summing up the infinite perturbation theory series we apply the Green function technique and the Heisenberg equation of motion of the electron annihilation and creation operators. The matrix elements of the transition processes include both the direct and crossing terms, so that there is no need to use the non-crossing approximation (NCA). The explicit expression of the electron transport current is derived.
Physical review letters, 2006
Numerical calculations are shown to reproduce the main results of recent experiments involving nonlocal spin control in quantum dots [Craig et al., Science 304, 565 (2004).]. In particular, the experimentally reported zero-bias-peak splitting is clearly observed in our studies. To understand these results, a simple ''circuit model'' is introduced and shown to qualitatively describe the experiments. The main idea is that the splitting originates in a Fano antiresonance, which is caused by having one quantum dot side connected in relation to the current's path. This scenario provides an explanation of the results of Craig et al. that is an alternative to the RKKY proposal, also addressed here.
Spin Blockade in Non-linear Transport through Quantum Dots
Europhysics Letters (EPL), 1994
The influence of excited levels on the nonlinear transport properties of a quantum dot weakly coupled to ideal leads is studied using a master-equation approach. A quantum mechanical model for interacting electrons is used to determine the spectrum of the dot. The current-voltage characteristic shows Coulomb blockade and additional finestructure that is related to the excited states of the correlated electrons. Asymmetric coupling to the leads causes asymmetric conductance peaks. It is demonstrated that spin selection rules can lead to regions of negative differential conductance.
Coulomb interaction and transport in tunnel junctions and quantum dots
Physica B: Condensed Matter, 1993
In the first part of the paper the AC conductance of a quasi-one-dimensional tunnel junction involving a potential barrier is calculated in linear response. Its frequency dependence is used to define a dynamical capacitance. The influence of phase breaking electron-phonon interactions is investigated. It is argued that Coulomb interaction is of minor importance at higher frequencies and that dynamic and static capacitances are the same. The argument provides a high-frequency limit for turnstile operation. In the second part, the quantum mechanical properties of few interacting electrons in quantum dots are considered. Including the spin degree of freedom, the spectral properties of up to four interacting electrons confined within a quasi-one-dimensional system of finite length with Coulomb interactions are investigated by numerical diagonalization. The limitations of the description in terms of a capacitance are discussed. For sufficiently low density the electrons become localized, forming a Wigner molecule. The energetically lowest excitations are identified as vibrational and tunneling modes, both being collective modes involving all the electrons.
Transport properties of strongly correlated electrons in quantum dots using a simple circuit model
Brazilian Journal of Physics, 2006
Numerical calculations are shown to reproduce the main results of recent experiments involving nonlocal spin control in nanostructures (N. J. Craig et al., Science 304, 565 (2004)). In particular, the splitting of the zero-bias-peak discovered experimentally is clearly observed in our studies. To understand these results, a simple "circuit model" is introduced and shown to provide a good qualitative description of the experiments. The main idea is that the splitting originates in a Fano anti-resonance, which is caused by having one quantum dot side-connected in relation to the current's path. This scenario provides an explanation of Craig et al.'s results that is alternative to the RKKY proposal, which is here also addressed.
Characteristics of Single Electron Transport in a Quantum Dots System
In this paper, we investigated the time-dependent single electron transport process in a quantum dots system. This system is consisted from three quantum dots linked with donor and acceptor electron as tight-bending model. The calculations of this system are done using time dependent Schrödinger equations, which is utilized theoretically to calculate the occupation probability for the all quantum dots and study the characteristics of this system. we observed that the occupation probabilities are oscillatory behavior with time, and the number of oscillations in the occupation probabilities is increased by increasing the coupling interaction strength. We also calculated the transmission probability density using a scattering theory, we observed that its peaks decreased at E = 0 with increasing the coupling interaction strength.
Theory of charge transport in a quantum dot tunnel junction with multiple energy levels
Physical Review B
Transport properties of nanoscale quantum dots embedded in a matrix connected with metallic electrodes are investigated theoretically. The Green's function method is used to calculate the tunneling current of an Anderson model with multiple energy levels, which is employed to model the nanoscale tunnel junction of concern. A closed form spectral function of a quantum dot or coupled dots ͑with arbitrary number of energy levels͒ embedded in a tunnel junction is derived and rigorously proved via the principle of induction. Such an expression can give an efficient and reliable way for analyzing the complicated current spectra of a quantum dot tunnel junction. Besides, it can also be applied to the coupled dots case, where the negative differential conductance due to the proximity effect is found. Finally, we investigate the case of bipolar tunneling, in which both electrons and holes are allowed to tunnel into the quantum dot, while optical emission occurs. We find dramatic changes in the emission spectra as the applied bias is varied.
Electronic Correlations in Transport through Coupled Quantum Dots
Physical Review Letters, 1999
The conductance through two quantum dots in series is studied using general qualitative arguments and quantitative slave-boson mean-field theory. It is demonstrated that measurements of the conductance can explore the phase diagram of the two-impurity Anderson model. Competition between the Kondo effect and the interdot magnetic exchange leads to a two-plateau structure in the conductance as a function to the gate voltage and a two or three peak structure in the conductance versus interdot tunneling. [S0031-9007(99)09017-1]
Correlation effects in the transport through quantum dots
We study the charge and heat transport through the correlated quantum dot with a finite value of the charging energy U = ∞ . The Kondo resonance appearing at temperatures below TK is responsible for several qualitative changes of the electric and thermal transport. We show that under such conditions the semiclassical Mott relation between the thermopower and electric conductivity is violated. We also analyze the other transport properties where a finite charging energy U has a significant influence. They are considered here both, in the limit of small and for arbitrarily large values of the external voltage eV = µL −µR and/or temperature difference TL −TR. In particular, we check validity of the Wiedemann-Franz law and the semiclassical Mott relation.