Search

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.

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 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.

Within the adiabatic approximation, it is shown that the effective electron-phonon interaction Hamiltonian for tunneling through a single molecular electronic level contains two different contributions. The interference of the two interaction channels can lead to either the enhancement or suppression of phonon generation. Conditions determining the intensity of excitation of vibrational modes of the molecule are found.

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.

The influence of many-particle interaction on tunneling characteristics in low dimensional structures is analyzed theoretically and investigated experimentally by means of STM/STS methods. It is shown that indirect interaction (trough band states of semiconductors) can often lead to increased tunneling conductivity for bias range where the direct interaction between impurity states is not significant. New method for preparation of electronic states with definite spin configuration on neighboring atoms is suggested. The energy splitting of opposite spin electrons can be about 0.5 - 1 eV. The different types of tunneling conductivity behavior in ultra small junction with superconductors is analyzed.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.