Electron polarization in quantum wells in a strong variable field

The wave function of an electron in a symmetric double quantum well placed in a strong time-periodic electric field is found, expressions for quasienergy functions are derived, and the dependence of the dipole moment on the average electric field is analyzed for the case where the average field remains constant. In the case of slow monotonic variation of the “constant” component of the electric field, the Schro dinger equation is solved by the WKB method. It is found that the dependence of the dipole moment on the average field is of a clearly nonlinear almost-periodic nature and that in the event of adiabatic monotonic variation of the average field there is a periodic relocation of the electron density from well to well with a small frequency proportional to the rate of variation of the average field. Zh. éksp. Teor. Fiz. 116, 217–235 (July 1999)     

Spectrum of indirect magnetoexcitons in coupled quantum wells

The indirect Mott exciton (spatially-separated electron and hole) in coupled quantum wells in crossed electric and magnetic fields is discussed. The exciton spectrum is calculated for the case where the distance between the quantum wells of the electron and hole is larger than the exciton Bohr radius. The magnetoexciton creation probability is calculated and its dependence on the electric field is found. The absorption of electromagnetic radiation between the indirect magnetoexciton levels in coupled quantum wells is discussed. Fiz. Tverd. Tela (St. Petersburg) 39, 2220–2223 (December 1997)     

Raman spectroscopy of resonance exciton tunneling in GaAs/AlAs superlattices in electric fields

Optical-resonance-Raman scattering by acoustic phonons is used to study the effect of an electric field on the state of excitons in GaAs/AlAs superlattices. When the energy of the exciting photon coincides with the energy of an exciton bound to Wannier-Stark states of a heavy hole and electron with Δn=0,±1, the acoustic Raman scattering is enhanced. Oscillations in the intensity of the Raman spectrum in the electric field are explained by resonance delocalization of the exciton ground state as it interacts with Wannier-Stark states of neighboring quantum wells or with Wannier-Stark states of a higher electron miniband. Fiz. Tverd. Tela (St. Petersburg) 40, 827–829 (May 1998)     

Interference in the photodecomposition of negative atomic hydrogen ions in an electric field

The quantum interference of electron waves in the photodecomposition of negative hydrogen ions in an external uniform electric field is examined. The structure of the photodetachment amplitudes is discussed. A simple analytic expression for the electron flux distribution is derived. Finally, it is shown that the structure of the electron flux is affected by the angular dependence of the wave function. Zh. éksp. Teor. Fiz. 112, 1574–1583 (November 1997)     

Glauber Dynamics for the Quantum Ising Model in a Transverse Field on a Regular Tree

Motivated by a recent use of Glauber dynamics for Monte Carlo simulations of path integral representation of quantum spin models (Krzakala et al. in Phys. Rev. B 78(13):134428, 2008), we analyse a natural Glauber dynamics for the quantum Ising model with a transverse field on a finite graph G. We establish strict monotonicity properties of the equilibrium distribution and we extend (and improve) the censoring inequality of Peres and Winkler to the quantum setting. Then we consider the case when G is a regular b-ary tree and prove the same fast mixing results established in Martinelli et al. (Commun. Math. Phys. 250(2):301–334, 2004) for the classical Ising model. Our main tool is an inductive relation between conditional marginals (known as the “cavity equation”) together with sharp bounds on the operator norm of the derivative at the stable fixed point. It is here that the main difference between the quantum and the classical case appear, as the cavity equation is formulated here in an infinite dimensional vector space, whereas in the classical case marginals belong to a one-dimensional space.     

Influence of the electric field on the electron transport in photosynthetic reaction centers

The effect of an electric field on the electron transfer in the bacterial reaction centers is investigated. The rate constants and quantum yields affected by the electric field for wild type (WT) and reaction center (RC) mutant of Rhodobacter capsulatus were computed. The dependence of the asymmetry of electron transfer in electric field on the temperature was evaluated. We found stable electron transfer for WT of the reaction center towards an electric field in comparison with the F(L121)D mutant of RC. We found quantum yields sensitive to the variation of the medium reorganization energy at low temperatures and strong electric fields. The quantum yields for unoriented RC samples were also calculated.     

Influence of the quantum size effect for grazing electrons on the electronic conductivity of metal films

The thickness dependence of the electronic conductivity of thin (5–150 nm) single-crystal (100) films of refractory metals is investigated at different temperatures ranging from 4.2 K to room temperature. Regions of square-root, quasilinear, and quadratic dependences are observed. The quasilinear thickness dependence is explained by the influence of quantum effects on the transverse motion of electrons in the case when electron scattering by the film surfaces dominates. For macroscopic film thicknesses 30–50 nm, much greater than the Fermi wavelength of an electron, quantum corrections to the electronic conductivity reach values of the order of 50%. This is a consequence of the quantum size effect for grazing electrons, which leads to an anomaly in electron scattering by the film surfaces. The region of the quadratic thickness dependence corresponds to the quantum limit, and the square-root region corresponds to the classical limit. The effect is explained in a quasiclassical two-parameter model (the effective angle α* for small-angle electrons and the parameter γ, equal to the ratio of this angle to the diffraction angle) that takes into account the diffraction angular limits for grazing electrons. The effect occurs for parameters α*≪1 and γ∼1 and differs from the “ordinary” quantum size effect. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 11, 693–698 (10 December 1997)     

Master Equation in Phase Space for a Spin in an Arbitrarily Directed Uniform External Field

The time evolution equation for the probability density function of spin orientations in the phase space representation of the polar and azimuthal angles is derived for the nonaxially symmetric problem of a quantum paramagnet subjected to a uniform magnetic field of arbitrary direction. This is accomplished by first rotating the coordinate system into one in which the polar axis is collinear with the field vector, then writing the reduced density matrix equation in the new coordinate system as an explicit inverse Wigner-Stratonovich transformation so that the phase space master equation may be derived just as in the axially symmetric case [Yu.P. Kalmykov et al., J. Stat. Phys. 131:969, 2008]. The properties of this equation, resembling the corresponding Fokker-Planck equation, are investigated. In particular, in the large spin limit, S→∞, the master equation becomes the classical Fokker-Planck equation describing the magnetization dynamics of a classical paramagnet in an arbitrarily directed uniform external field.     

Multiphonon capture of carriers in parabolic quantum wells in a constant electric field

The zero-radius potential model is used to investigate multiphonon (radiationless) transitions between bound states of a parabolic quantum well (PQW) in a constant electric field whose intensity vector is perpendicular to the PQW surface. It is shown that thermal-capture thicknesses depend significantly on the magnitude and direction of the electric field and on the position of the impurity in the spatially bounded system. Fiz. Tverd. Tela (St. Petersburg) 40, 1126–1129 (June 1998)     

First Quantum Corrections to the Classical Partition Function for a Non-Relativistic Electrodynamical System

The classical partition function for a system in thermodynamical equilibrium formed by N identical non-relativistic particles interacting through Coulomb potentials and with the dynamical electromagnetic field is studied. It is proved that the dynamical or transverse EM degrees of freedom decouple from the particle ones. It is also shown that this decoupling does to take place in the quantum mechanical partition function. The leading quantum corrections to the classical partition function are explicitly given. Such corrections are shown to be determined by instantaneous dipole-dipole coulombic interactions and by self-energy effects, and to receive no contribution from the interaction among different particles mediated by the dynamical EM field.     

Differential thermopower of a superlattice in a strong electric field

The effect of an electric field on the differential thermopower α(E) of a one-dimensional superlattice is investigated in the semiclassical approximation. A nonmonotonic temperature dependence of α(0) is established for a degenerate electron gas. It is shown that, in principle, an electric field can be used to control the thermoelectric properties of superlattices. Fiz. Tverd. Tela (St. Petersburg) 41, 1314–1316 (July 1999)     

Wegner-type Bounds for a Two-particle Lattice Model with a Generic “Rough” Quasi-periodic Potential

In this paper, we consider a class of two-particle tight-binding Hamiltonians, describing pairs of interacting quantum particles on the lattice ℤ ^d , d ≥ 1, subject to a common external potential V(x) which we assume quasi-periodic and depending on auxiliary parameters. Such parametric families of ergodic deterministic potentials (“grands ensembles”) have been introduced earlier in Chulaevsky (2007), in the framework of single-particle lattice systems, where it was proved that a non-uniform analog of the Wegner bound holds true for a class of quasi-periodic grands ensembles. Using the approach proposed in Chulaevsky and Suhov (Commun Math Phys 283(2):479–489, 2008), we establish volume-dependent Wegner-type bounds for a class of quasi-periodic two-particle lattice systems with a non-random short-range interaction.     

Momentum dependence of the dimensionality of the electronic states in heterostructures

Bound states of electrons (holes) in quantum wells and wires with asymmetric barriers can exist in bounded regions of two-and one-dimensional momentum space, respectively. As the corresponding momentum increases, both the disappearance (increase of dimensionality) and appearance (decrease of dimensionality) of bound states as well as the existence of a sequence of several such transformations of dimensionality are possible. In the case of anisotropic effective masses in the quantum wells and barriers, the forms of the lines of disappearance and appearance of bound states are different from the forms of the isoenergy lines. Therefore there is a finite energy interval (i.e., electron density interval) where bound states exist on only a part of an isoenergy line. The dimensionality of the states can be controlled with an electric field; this should be observable in a number of the experiments discussed. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 2, 188–193 (25 January 1997)     

Quantum Brownian Motion on Non-Commutative Manifolds: Construction,Deformation and Exit Times

We begin with a review and analytical construction of quantum Gaussian process (and quantum Brownian motions) in the sense of Franz (The Theory of Quantum Levy Processes, [math.PR], 2009), Schürmann (White noise on bioalgebras. Volume 1544 of Lecture Notes in Mathematics. Berlin: Springer-Verlag, 1993) and others, and then formulate and study in details (with a number of interesting examples) a definition of quantum Brownian motions on those non-commutative manifolds (a la Connes) which are quantum homogeneous spaces of their quantum isometry groups in the sense of Goswami (Commun Math Phys 285(1):141–160, 2009). We prove that bi-invariant quantum Brownian motion can be ‘deformed’ in a suitable sense. Moreover, we propose a non-commutative analogue of the well-known asymptotics of the exit time of classical Brownian motion. We explicitly analyze such asymptotics for a specific example on non-commutative two-torus A_q{\mathcal{A}_\theta} , which seems to behave like a one-dimensional manifold, perhaps reminiscent of the fact that A_q{\mathcal{A}_\theta} is a non-commutative model of the (locally one-dimensional) ‘leaf-space’ of the Kronecker foliation.     

Optical absorption by small metallic particles

We study theoretically the dependence of absorption by small metallic particles on particle shape and wave polarization in the IR frequency range. We examine the electric and magnetic absorption by small particles. The particles may be either larger or smaller than the electron mean free path. We show that for asymmetric particles smaller than the mean free path the light-induced conductivity is a tensor. We also show that the total absorption and the electric-to-magnetic absorption ratio are strongly dependent on particle shape and wave polarization. Finally, we construct curves representing the dependence of the ratio of the electric and magnetic contributions to absorption on the degree of particle asymmetry for different wave polarizations. Similar curves are constructed for the ratio of the components of the light-induced conductivity tensor. Zh. éksp. Teor. Fiz. 112, 661–678 (August 1997)     

Effect of a dust component on the rates of elementary processes in low-temperature plasmas

Elementary processes in dusty, beam-driven plasma discharges are studied experimentally and theoretically for the first time. A theoretical model is constructed for a beam-driven plasma containing macroscopic particles. The effect of macroscopic particles on the electron energy distribution function is estimated assuming a Coulomb field for the particles. The resulting rate of electron-ion recombination on the macroscopic particles is compared with the electron loss constant calculated from the electron energy distribution function with an electron absorption constant in the orbital-motion approximation. This approximation, which is valid in the collisionless case, is found to work satisfactorily beyond its range of applicability. The distributions of the charged particles and electric fields created by macroscopic particles in a helium plasma are determined. The experimental data demonstrate the importance of secondary emission by high-energy electrons. Zh. éksp. Teor. Fiz. 115, 2020–2036 (June 1999)     

Bound States in the Quantum Scalar Electrodynamics

The next relativistic correction to α to for bound state mass of two charged scalar particles is calculated in the quantum scalar electrodynamics by the functional integral method. Contribution of the “nonphysical” time variable turned out to be important and leads to nonanalytic dependence of the bound state mass on α.