Interplay between the Coulomb blockade and resonant tunneling studied by the Keldysh Green’s-function method (original) (raw)

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.

Energy-Dependent Tunneling in a Quantum Dot

Physical Review Letters, 2007

We present measurements of the rates for an electron to tunnel on and off a quantum dot, obtained using a quantum point contact charge sensor. The tunnel rates show exponential dependence on drain-source bias and plunger gate voltages. The tunneling process is shown to be elastic, and a model describing tunneling in terms of the dot energy relative to the height of the tunnel barrier quantitatively describes the measurements.

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.

Charge on the quantum dot in the presence of tunneling current

Solid State Communications, 2000

The calculation of the charge present in central region of the double barrier structure at non-equilibrium conditions is discussed. We propose here a simple method to calculate non equilibrium Green's functions which allows consistent calculations of retarded and distribution functions. To illustrate the approach we calculate the charge on the quantum dot coupled via tunnel barriers to two external leads having different chemical potentials µ L and µ R. The obtained results have been compared with other approaches existing in the literature. They all agree in the equilibrium situation and the departures grow with increasing the difference µ L − µ R .

Quantum Coulomb blockade in gate-controlled quantum dots

Microelectronic Engineering, 2000

A theoretical description is presented for transport-spectroscopy experiments with gate-controlled quantum dots. We havë obtained a self-consistent solution of the Poisson-Schrodinger problem for the quantum-dot nanodevice, calculated the confinement potential, and determined the conditions for the single-electron tunneling, that is closely related with the quantum Coulomb blockade. We have also performed calculations for the gate-controlled quantum dot under an external magnetic field and obtained a very good agreement with the experimental results.

Theoretical and experimental investigations of Coulomb blockade in coupled quantum dot systems

Journal of Physics: Condensed Matter, 2008

Two strongly coupled quantum dots are theoretically and experimentally investigated. In conductance measurements on a GaAs based low-dimensional system additional features to the Coulomb blockade have been detected at low temperatures. These regions of finite conductivity are compared with theoretical investigations of a strongly coupled quantum dot system and good agreement between the theoretical and the experimental results has been found.

Coherent tunnelling through two quantum dots with Coulomb interaction

Journal of Physics-condensed Matter, 1996

The coherent conductance and current is calculated through two quantum dots using the Hubbard model for a single level per spin. The occurrence of negative differential conductance is demonstrated. The Ohmic conductance is calculated for dots with equally spaced levels. Transport is determined by matching energy levels, even when they do not occur at the charge degeneracy points.

Electronic transport of a T-shaped double-quantum-dot system in the Coulomb blockade regime

The European Physical Journal B, 2013

We studied the electronic transport properties of a T-shaped double-quantum-dot system in the Coulomb blockade regime when the onsite Coulomb interaction parameters U1 and U2 have finite values in both component dots. Our analysis is done in the so-called beyond Hartree-Fock approximation that includes contributions related to both normal and mixed averages of various number-like operators in the system. We provide an analytic formula for the main's dot Green function in the case of large onsite Coulomb interaction parameters (U1 = U2 → ∞), and find that with a good approximation, this limit is realized when the ratio U1/t = U2/t ≥ 30, t being the interdot electron tunneling between the two component dots of the structures. In the most general situation of the Coulomb blockade regime (U1 = U2) the system conductivity presents two dips corresponding to the Fano-Kondo effect and the system's shot noise and electronic current present a series of plateaus that should be visible in experimental setups.