P. I. Arseyev

Correlation induced switching of the local spatial charge distribution in a two-level system

It was found that tunneling current through a nanometer scale structure with strongly coupled localized states causes spatial redistribution of localized charges induced by Coulomb correlations. We present here theoretical investigation of this effect by means of Heisenberg equations for localized states electron filling numbers. This method makes it possible to take into account pair correlations of local electron density exactly. It is shown that inverse occupation of the two-level system caused by Coulomb correlations appears in particular range of applied bias. Described effects can give a possibility of charge manipulation in the proposed system. We also expect that described results can be observed in tunneling structures with impurities or with small quantum dots.

Nonadiabatic electron charge pumping in coupled semiconductor quantum dots

The possibility of nonadiabatic electron pumping in the system of three coupled quantum dots (QDs) attached to the leads is discussed. We have found out that periodical changing of energy level position in the middle QD results in non-zero mean tunneling current appeared due to nonadiabatic non-equilibrium processes. The same principle can be used for fabrication of a new class of semiconductor electronic devices based on non-stationary non-equilibrium currents. As an example we propose a nanometer quantum emitter with non-stationary inverse level occupation achieved by electron pumping.

Tunneling current induced phonon generation in nanostructures

We analyze generation of phonons in tunneling structures with two electron states coupled by electron-phonon interaction. The conditions of strong vibration excitations are determined and the dependence of nonequilibrium phonon occupation numbers on the applied bias is found. For high vibration excitation levels, a self-consistent theory for the tunneling transport is presented.

External field induced switching of a tunneling current in coupled quantum dots

We investigated the tunneling current peculiarities in the system of two quantum dots that are coupled by means of the external field and are weakly connected to the electrodes in the presence of Coulomb correlations. It was found that tuning of the Rabi frequency induces fast multiple tunneling current switching and leads to the negative tunneling conductivity. Special role of multielectron states was demonstrated. Moreover we revealed conditions for bistable behavior of the tunneling current in the coupled quantum dots with Coulomb correlations.

Identifying the electronic properties of the Ge(111)-(2×1) surface by low-temperature scanning tunneling microscopy

We present the results of our low-temperature scanning tunneling microscopy (STM) investigation of the clean Ge(111) surface. Our experiments enable, for the first time, STM observation of one-dimensional surface screening around surface defects. We identify the dominating role of surface states in the low-temperature STM imaging as well as the important influence of nonequilibrium kinetics on the measured tunneling spectra.

The effects of nonequilibrium charge distribution in scanning tunneling spectroscopy of semiconductors

Results are presented from a low-temperature scanning tunneling microscopy (STM) investigation of III-V semiconductor surfaces cleaved in situ along a (110) plane. The STM topographic images reveal the presence of surface charge structures. The possibility of their observation depends on the charge state of the apex of the STM tip. Peaks are also observed in the local tunneling conductivity spectra. The energy position of these peaks and the energy position of the edges of the band gap change with distance from the defect. A theoretical model is proposed which demonstrates that the experimental scanning tunneling spectroscopy (STS) data can be explained by effects due to a nonequilibrium electron distribution in the contact area, which gives rise to localized charges. In this model the on-site Coulomb repulsion of localized charges and their interaction with semiconductor electrons are treated self-consistently.

Effects of electron-phonon interaction in tunneling processes in nanostructures

Tunneling through a system with two discrete electron levels coupled by electron-phonon interaction is considered. The interplay between elastic and inelastic tunneling channels is analyzed not only for weak electron-phonon coupling but also for strong coupling in the resonant case. It is shown that the intensity and width of peaks in the tunneling conductivity is strongly influenced by nonequilibrium effects.

On the density of states for the Hubbard model: pseudo-particle Keldysh diagram method - an alternative to DMFT?

It is shown how to construct Keldysh diagram technique for pseudo-particle approach to the Hubbard model. We propose self-consistent equations for pseudo particle and electron Green’s functions in Keldysh diagram technique. Nonlocal effects (spatial dispersion) are included in single impurity problem in this method. Thus we can get rid of the artificial central peak (of Kondo type) in the density of states which is inevitable in Dynamical Mean Field Theory (DMFT). The changes in the density of states for 2D Hubbard model due to variation of Coulomb repulsion U and electron concentration are analyzed.

Bias voltage dependent shift of the atomic-scale structure of a Ge(111)-(2 × 1) reconstructed surface measured by low temperature scanning tunneling microscopy

The results of low temperature scanning tunneling microscopy (STM) investigations of a clean Ge(111) surface are presented. Bias dependent shifts of the atomic-scale structure caused by the (2 × 1) reconstruction of the Ge(111) surface are observed. A detailed comparison of experimental data with theoretical predictions based on the π-bonded chain model indicates that inelastic tip-sample interaction plays a significant role in STM imaging of the Ge(111)-(2 × 1) reconstructed surface.

Diagnostics of many-particle electronic states: Non-stationary currents and residual charge dynamics

We propose the method for identifying many particle electronic states in the system of coupled quantum dots (impurities) with Coulomb correlations. We demonstrate that different electronic states can be distinguished by the complex analysis of localized charge dynamics and non-stationary characteristics. We show that localized charge time evolution strongly depends on the properties of initial state and analyze different time scales in charge kinetics for initially prepared singlet and triplet states. We reveal the conditions for existence of charge trapping effects governed by the selection rules for electron transitions between the states with different occupation numbers.