We propose a technique for processing noisy spectral data that implements a mathematically based selection of sharp signal peaks on an unknown smooth background, for which there is no reliable theoretical model. The fundamental concept of the technique is to construct an optimizing functional that gives the most probable parameters of spectral lines. Unlike the Tikhonov regularization method, where a smooth unknown function is extracted from a noisy signal, we consider the problem of regularizing the superposition of a smooth background function with sharp peaks. The proposed approach provides an algorithm for processing experimental data that makes it possible to filter out random noise and determine both the peak parameters and the background function with good accuracy. Finding the optimal regularization parameters is based on a priori assumptions about the smoothness of the background function and the statistical properties of random noise.

Light scattering spectroscopy is a powerful tool for studying various media, but interpretation of its results requires a detailed knowledge of how media excitations are coupled to electromagnetic waves. In electrically conducting media, an accurate description of propagating electromagnetic waves is a non-trivial problem because of non-local light-matter interactions. Among other consequences, the non-locality gives rise to the anomalous (ASE) and superanomalous (SASE) skin effects. As is well known, ASE is related to an increase in the electromagnetic field absorption in the radio frequency domain. This work demonstrates that the Landau damping underlying SASE gives rise to another absorption peak at optical frequencies. In contrast to ASE, SASE suppresses only the longitudinal field component, and this difference results in the strong polarization dependence of the absorption. The mechanism behind the suppression is generic and is observed also in plasma. Neither SASE, nor the corresponding light absorption increase can be described using popular simplified models for the non-local dielectric response.

p - i - n semiconductor heterostructures are common optoelectronic devices with numerous applications hinging on the non-trivial kinetics of photoexcited charge carriers within them. One such effect manifests itself as an oscillation of the photocurrent versus the applied bias voltage and has been qualitatively studied recently. However, a model that would explain the experimentally observed magnitude of the oscillations is, to the best of our knowledge, still absent. In the present work we consider a model wherein electrons from the highly-doped p -region are resonantly captured into 2D states of the triangular quantum well formed by the undoped i -region via scattering on impurities. We find that the rate of capture into 2D states is determined by the form of the wave function of these states and increases sharply when the tail of the wave function penetrates deeply into the highly doped region, resulting in a sharp increase in the photocurrent. Our analysis of the dependence of the positions of the photocurrent maxima versus bias voltage shows good agreement with experiments and confirms the applicability of our model.

The behavior of the photocurrent in GaAs/AlAs p-i-n-heterostructures is studied in a magnetic field parallel to the heterolayers in the wavelength range from 395 to 650 nm. A strong dependence of the non-oscillating component of the photocurrent on the radiation wavelength associated with the suppression of the diffusion current by the magnetic field was found. It is shown that the behavior of the oscillating component of the photocurrent in a magnetic field does not depend on the wavelength of light and is determined by the transfer of electrons through the dimensional quantization level in a triangular near-barrier well. It is shown that the suppression of the oscillating component by the magnetic field is due to the smearing of the level in the triangular well due to the motion of electrons parallel to the walls of the well and perpendicular to the magnetic field. Keywords: heterostructures, photoconductivity, magnetotunneling.

The behavior of the photocurrent in GaAs / AlAs p-i-n heterostructures is studied in a magnetic field parallel to the heterolayers in the wavelength range from 395 to 650 nm. A strong dependence of the non-oscillating component of the photocurrent on the radiation wavelength associated with the suppression of the diffusion current by the magnetic field was found. It is shown that the behavior of the oscillating component of the photocurrent in a magnetic field does not depend on the wavelength of light and is determined by the transfer of electrons through the dimensional quantization level in a triangular near-barrier well. It is shown that the suppression of the oscillating component by the magnetic field is due to the smearing of the level in the triangular well due to the motion of electrons parallel to the walls of the well and perpendicular to the magnetic field.

We consider tunneling of spinless electrons from a single-channel emitter into an empty collector through an interacting resonant level of the quantum dot (QD). When all Coulomb screening of sudden charge variations of the dot during the tunneling is realized by the emitter channel, the system is mapped onto an exactly solvable model of a dissipative qubit. The qubit density matrix evolution is described with a generalized Bloch equation which permits us to count the tunneling electrons and find the charge transfer statistics. The two generating functions of the counting statistics of the charge transferred during the QD evolutions from its stationary and empty state have been expressed through each other. It is used to calculate the spectrum of the steady current noise and to demonstrate the occurrence of the bifurcation of its single zero-frequency minimum into two finite-frequency dips due to the qubit coherent dynamics.

Tunneling of spinless electrons from a single-channel emitter into an empty collector through an interacting resonant level of the quantum dot (QD) is studied, when all Coulomb screening of charge variations on the dot is realized by the emitter channel and the system is mapped onto an exactly solvable model of a dissipative qubit. In this model we describe the qubit density matrix evolution with a generalized Lindblad equation, which permits us to count the tunneling electrons and therefore relate the qubit dynamics to the charge transfer statistics. In particular, the coefficients of its generating function equal to the time-dependent probabilities to have the fixed number of electrons tunneled into the collector are expressed through the parameters of a non-Hermitian Hamiltonian evolution of the qubit pure states in-between the successive electron tunneling events. From the leading asymptotics of the cumulant generating function (CGF) linear in time we calculate the Fano factor and the skewness and establish their relation to the extra average and the second cumulants, respectively, of the charge accumulated during the QD evolution from its empty and stationary states, which are defined by the next-to-leading term of the CGF asymptotics. The relation explains the origin of the sub-Poisson and super-Poisson shot noise in this system and shows that the super-Poisson signals existence of a nonmonotonous oscillating transient current and the qubit coherent dynamics. The mechanism is illustrated with particular examples of the generating functions, one of which coincides in the large time limit with the generating function of the 1/3 fractional Poisson distribution realized without the fractional charge tunneling.

Resonance magnetic tunneling in heterostructures formed by graphene single sheets separated by a hexagonal boron nitride barrier and bounded by two gates has been investigated in a strong magnetic field, which has allowed observing transitions between spin- and valley-split Landau levels with various indices belonging to different graphene sheets. An unexpected increase with the temperature in the interlayer tunneling conductance owing to transitions between the Landau levels in strong magnetic fields cannot be explained by existing theories.

We propose a new Auger-like mechanism for energy relaxation in quantum dots (QD) driven by resonant scattering of delocalized wetting layer (WL) carriers. It is demonstrated that resonant scattering leads to a considerable increase in the relaxation rate that can explain experimentally obtained relaxation rates. Analytical results for the relaxation rate are obtained for rectangular dots revealing a weak logarithmic dependence on the dot depth and level density. Comparing results for a rectangular and a parabolic QD model we conclude that the relaxation rate is not very sensitive to a chosen model.

We consider tunneling of spinless electrons from a single-channel emitter into an empty collector through an interacting resonant level of the quantum dot. When all Coulomb screening of sudden charge variations of the dot during the tunneling is realized by the emitter channel, the system is described with an exactly solvable model of a dissipative qubit. To study manifestations of the coherent qubit dynamics in the collector ac response we derive a solution to the corresponding Bloch equation for the model quantum evolution in the presence of the oscillating voltage of frequency. and calculate perturbatively the ac response in the voltage amplitude. We have shown that in a wide range of the model parameters the coherent qubit dynamics results in the nonzero frequencies resonances in the amplitudes dependence of the ac harmonics and in the jumps of the harmonics phase shifts across the resonances. In the first order the ac response is directly related to the spectral decomposition of the corresponding transient current and contains only the first. harmonic, whose amplitude exhibits resonance at omega = omega(I), where.I is the qubit oscillation frequency. In the second order we have obtained the 2. harmonic of the ac response with resonances in the frequency dependence of its amplitude at omega(I), omega(I)/2 and zero frequency and also have found the frequency dependent shift of the average steady current.

We consider tunneling of spinless electrons from a single-channel emitter into an empty collector through an interacting resonant level of the quantum dot. When all Coulomb screening of sudden charge variations of the dot during the tunneling is realized by the emitter channel, the system is described with an exactly solvable model of a dissipative qubit. To study manifestations of the coherent qubit dynamics in the collector a.c. response we derive solution to the corresponding Bloch equation for the model quantum evolution in the presence of the oscillating voltage of frequency perturbatively thea.c.response in the voltage amplitude. We have shown that in a wide range of the model parameters the coherent qubit dynamics results in the non-zero frequencies resonances in the amplitudes dependence of thea.c.harmonics and in the jumps of the harmonics phase shifts across the resonances. In the first order thea.c.response is directly related to the spectral decomposition of the corresponding transient current and contains only the firstωharmonic, whose amplitude exhibits resonance atω=ω_I , whereω_Iis the qubit oscillation frequency. In the second order we have obtained the2 ωharmonic of thea.c.response with resonances in the frequency dependence of its amplitude atω_I,ω_I/2and zero frequency and also have found the frequency dependent shift of the average steady current.

It is commonly assumed that surface plasmon-polariton (SPP) excitations on a metal-dielectric interface decay exponentially inside the metallic sample. Here, we show that in a wide spectral interval the SPP field decays much slower, being inversely proportional to the distance to the interface modified by an additional logarithmic factor. This dependence differs from the standard anomalous skin effect and is provisionally referred to as superanomalous. Its origin is the nonlocality and the logarithmic singularity of the dielectric permittivity in metals. This type of decay is pronounced for SPP modes of higher frequencies, but it is suppressed for light waves.

This work investigates the influence of non-locality in the dielectric response on the spatio-temporal evolution of surface plasmon-polaritons (SPP). SPP excitations are coherently generated by a quantum scatterer in the vicinity of a flat metal interface. It is demonstrated that the excited non-equilibrium SPP population eventually splits into two coherent localized wave packets. One packet propagates along the interface and the other is centered in the vicinity of the scatter. The amplitude of both waves slowly decreases due to several relaxation mechanisms, with the Landau damping being the strongest. The non-locality of the metallic dielectric response considerably influences spatial profiles of the plasmon field intensity, in particular, leading to coherent spatio-temporal oscillations between the two wave packets.

We investigate the dynamics of a quantum emitter (quantum dot) placed in the vicinity of a flat metal surface. The dynamics is induced by the coupling between the emitter and surface plasmon-polaritons. The plasmon-polariton modes are described within a continuous media model with a nonlocal Lindhard-type dielectric response of the metal. The analytic solution of the dynamical equations is obtained in the rotating wave approximation. The results demonstrate a considerable influence of the nonlocality of the electromagnetic response and the Landau damping in the metal. In particular, the relaxation dynamics is characterized by two distinct times that may differ by large amounts as a consequence of the nonlocality of the response. It is also shown that one of the contributions to the relaxation can have a power-law long-time asymptote, leading to notable changes in the dynamical pattern.

We have theoretically studied dynamics of the two-dimensional electron system (2DES) placed in a strong laterally non-uniform magnetic field, which appears due to ferromagnetic film on the top of heterostructure.It is shown that lateral inhomogeneity of a strong magnetic field allows itself "magnetic gradient" or special magnetic-edge magnetoplasmons.This mechanism is different from usual "density gradient" edge magnetoplasmons.We have solved self-consistently Poisson equation for non-uniform density distribution of the 2DES for realistic heterostructure together with hydrodynamic equation of 2D Fermi liquid.As a result eigen value problem has been obtained that corresponds to the motion of charge density wave perpendicular to magnetic gradient.It is shown that for non-monotonic distribution of magnetic field "magnetic gradient" magnetoplasmons may move in both directions.To solve eigen value problem we have compared two types of numerical approaches: first is grid method that diagonalizes large Hermitian matrix and second is semi-analytical approach that expand each eigen mode on the set of orthogonal functions.

We consider in this work many-body enhanced electron tunneling through an InAs quantum dot in a magnetic field applied perpendicular to the tunneling direction. We have examined in details the anisotropic behavior of the amplitude and shape of the resonant peaks.

We study the magneto-resistance of a two-dimensional electron systems in a wide quantum well. We have considered two occupied subbands subjected to the tilted magnetic field in the regime of the magneto-inter-subband oscillations. We report on both experimental and theoretical studies of such a phenomenon and deduced information on the inter-subband energy gap in the presence of the in-plane magnetic field.

It is shown that laterally inhomogeneous strong magnetic field applied to otherwise spatially homogeneous two-dimensional electron system (2DES) allows "magnetic gradient" or special magnetic-edge magnetoplasmons (MEMPs). This mechanism is different from usual "density gradient" edge magnetoplasmons. Symmetric and antisymmetric families of MEMPs are obtained. They are localized at magnetic field inhomogeneity (magnetic-edge). Both symmetric and antisymmetric MEMPs have the modes of opposite chirality.

We discuss in detail spin-polarized electronic structure calculations for the 1 × 1 YBa2Cu3O7/PrBa2Cu3O7 superlattice. Our results are based on the full-potential linear augmented plane wave method and the generalized gradient approximation for the exchange–correlation functional. The on-site Coulomb interaction affecting the correlated Cu 3d and Pr 4f electrons is taken into consideration. At first glance the YBa2Cu3O7/PrBa2Cu3O7 interface appears to be inert, i.e., the electronic states do not show a clear sign of interaction between the two component materials. Nonetheless, a total energy analysis points to a significant modification of the magnetic coupling in the vicinity of the interface due to the relaxation of the electronic structure.