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We report the results of theoretical investigations of the tunneling current noise spectra through a single-level impurity both in the presence and in the absence of electron–phonon interaction based on the nonequilibrium Green’s functions formalism. We show that due to the quantum nature of tunneling, the Fano factor is dramatically different from the Poisson limit both in the presence and in the absence of inelastic processes. The results are demonstrated to be sensitive to the tunneling contact parameters.

In a system of N interacting single-level quantum dots (QDs), we study the relaxation dynamics and the current–voltage characteristics determined by symmetry properties of the QD arrangement. Different numbers of dots, initial charge configurations, and various coupling regimes to reservoirs are considered. We reveal that effective charge trapping occurs for particular regimes of coupling to the reservoir when more than two dots form a ring structure with the C N spatial symmetry. We reveal that the effective charge trapping caused by the C N spatial symmetry of N coupled QDs depends on the number of dots and the way of coupling to the reservoirs. We demonstrate that the charge trapping effect is directly connected with the formation of dark states, which are not coupled to reservoirs due to the system spatial symmetry C N. We also reveal the symmetry blockade of the tunneling current caused by the presence of dark states.

It is shown how the general formulas of the nonequilibrium diagram technique can be used in problems of tunnel planar structures described in the effective mass approach. The relation between such a “continual” approach and the tunneling Hamiltonian method is established, and the applicability conditions for this method are determined. The effects beyond the applicability limits of the tunneling Hamiltonian method, which can be described by the continual approach, are considered.

We found analytical solution for the time evolution of localized electron density in a system of two coupled single-level quantum dots (QDs) connected with continuous spectrum states in the presence of Coulomb interaction. This solution takes into account QD electrons correlation functions of all orders neglecting any correlations between localized and conduction electron filling numbers. We demonstrated that several time scales with the strongly different relaxation rates appear in the system for a wide range of the Coulomb interaction value. We revealed that specific non monotonic behavior of charge relaxation in QD takes place due to Coulomb correlations. We also found out that besides the usual charge oscillations with the period determined by the detuning between the energy levels of the QDs a new effect of period doubling appears in the presence of Coulomb interaction at particular range of the system parameters., 9 pages, 6 figures

We demonstrate that the tunneling current flowing through a system with Coulomb correlations leads to a charge redistribution between the different localized states. A simple model consisting of two electron levels is analyzed by means of the Heisenberg equations of motion taking correlations of electron filling numbers in localized states into account exactly in all orders. We consider various relations between the Coulomb interaction and localized electron energies. Sudden jumps of the electron density at each level in a certain range of the applied bias are found. We find that for some parameter range, inverse occupation in the two-level system appears due to Coulomb correlations. It is also shown that Coulomb correlations lead to the appearance of negative tunneling conductivity at a certain relation between the values of tunneling rates from the two electron levels.

It is shown how effective Hamiltonians are constructed in the framework of the adiabatic approach to the electron–vibration interaction in electron tunneling through single molecules. Methods for calculating tunneling characteristics are discussed and possible features resulting from the electron–vibration coupling are described. The intensity of vibrations excited by a tunneling current in various systems is examined.

The results of UHV STM investigations of tunneling current noise spectra in the vicinity of individual impurity atoms on the InAs(110) surface are reported. It was found that the power law exponent of 1/f α noise depends on the presence of an impurity atom in the tunneling junction area. This is consistent with the proposed theoretical model considering tunneling current through a two-state impurity complex model system taking into account many-particle interaction.

We report on the direct observation by low-temperature scanning tunneling microscopy and scanning tunneling spectroscopy of the d orbitals of a Mn p-type impurity appearing on a cleaved InAs(110) surface. We show that the crucial interplay between nonequilibrium charging effects and many-particle interaction leading to Coulomb singularities provides a consistent description of the experimental results.

Nonequilibrium interaction effects of two Hubbard-Anderson impurities have been experimentally studied by means of STM/STS methods and theoretically analyzed using a self-consistent approach based on the Keldysh formalism.

Interaction of two localized impurity states of Si atoms at a GaAs surface was studied by scanning tunneling microscopy and spectroscopy. The effects of a twofold “switching” on and off of the states of each of the interacting atoms, the tunneling-interaction-induced mutual level pulling of these states, and the level stabilization near EF were observed. These effects are explained in terms of the extended Anderson model.

We have performed voltage dependent imaging and spatially resolved spectroscopy on the (110) surface of Te doped GaAs single crystals with a low temperature scanning tunneling microscope (STM). A large fraction of the observed defects are identified as Te dopant atoms which can be observed down to the fifth subsurface layer. For negative sample voltages, the dopant atoms are surrounded by Friedel charge density oscillations. Spatially resolved spectroscopy above the dopant atoms and above defect free areas of the GaAs (110) surface reveals the presence of conductance peaks inside the semiconductor band gap. The appearance of the peaks can be linked to charges residing on states which are localized within the tunnel junction area. We show that these localized states can be present on the doped GaAs surface as well as at the STM tip apex., 8 pages, 8 figures, accepted for publication in PRB