P. I. Arseev

Many-particle interaction in tunneling spectroscopy of impurity states on the InAs(110) surface

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.

Non-Equilibrium Tunneling Effects of Interacting Hubbard-Anderson Impurities

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.

Electron interaction with vibrational modes in tunneling through a single molecular electronic level

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.

Tunneling current noise spectra of biased impurity with a phonon mode

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.

Spatial-symmetry-induced dark states and charge trapping effects in the coupled quantum dots

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 CN spatial symmetry. We reveal that the effective charge trapping caused by the CN 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 CN. We also reveal the symmetry blockade of the tunneling current caused by the presence of dark states.

Nonstationary effects in the system of coupled quantum dots influenced by Coulomb correlations

We investigate the time evolution of filling numbers of localized electrons in the system of two coupled single-level quantum dots (QDs) connected with the continuous-spectrum states in the presence of Coulomb interaction. We consider correlation functions of all orders for electrons in the QDs by decoupling higher-order correlations between localized and band electrons in the reservoir. We analyze different initial charge configurations and consider Coulomb correlations between localized electrons both within the dots and between the different dots. We reveal the presence of a dynamical charge trapping effect in the first QD in the situation where both dots are occupied at the initial instant. We also find an analytic solution for the time-dependent filling numbers of the localized electrons for a particular configuration of the dots.

Optical conductivity of a two-band superconductor

Within the two-band superconductor model, which is a generalization of the standard BCS model to the case of a complicated crystal structure, an expression has been obtained for the conductivity of the superconductor at an arbitrary frequency of the external electromagnetic field. This expression has been derived using the microscopic theory in the framework of the diagram technique for nonequilibrium processes. The σ(ω) dependencies calculated for T = 0 are compared with the results of single-band models with the s and d symmetries of the order parameter. It has been shown that the behavior of the optical conductivity as a function of the frequency depends strongly on the doping level.

Optical sum rule in multiband superconductors

In the standard Bardeen-Cooper-Schrieffer model, the optical sum rule establishes the relation between the superfluid density and the change in the integral of the real part of the conductivity over the frequency after the transition to the superconducting state. In conventional low-temperature superconductors, these two values become equal if the conductivity is integrated up to a frequency of the order of several widths of the superconducting gap. Optical experiments for high-Tc cuprate superconductors performed by many research groups over the world demonstrate that the integration up to a much higher frequency (of the order of the band width) is needed to reproduce the spectral weight of the superfluid component. An interpretation of these experiments has been proposed with allowance for the complex crystal structure of cuprates, in which several orbitals of different symmetries approach the Fermi level.

Effect of symmetry of the electron states of HTSC on the current-voltage characteristics of SIS junctions

The current-voltage (IV) characteristics of SIS junctions are calculated in the framework of a multiband model with an anisotropic effective order parameter of HTSC. The results of calculations show that the shape of the IV characteristic and of the density of electron states changes significantly depending on the parameters of the model. A theoretical explanation is proposed for the experimentally observed s-like behavior of the IV characteristics of SIN and SIS junctions with BSCCO-type superconductors. The dependence of the superconducting peak asymmetry on the mutual arrangement of the bands is analyzed. The difference between the obtained results and the results of one-band models with the s and d symmetries of the order parameter is discussed.

Particular type of a gap in the spectrum of multiband superconductors

We show that in contrast to the free electron model (standard BCS model), a particular gap in the spectrum of multiband superconductors opens at some distance from the Fermi energy, if conduction band is composed of hybridized atomic orbitals of different symmetries. This gap has composite superconducting-hybridization origin, because it exists only if both the superconductivity and the hybridization between different kinds of orbitals are present. Therefore, for many classes of superconductors with multiorbital structure such spectrum changes should take place. These particular changes in the spectrum at some distance from the Fermi level result in slow convergence of the spectral weight of the optical conductivity even in quite conventional superconductors with isotropic s-wave pairing mechanism.