Interaction of strongly correlated electrons and acoustical phonons

We investigate the interaction of correlated electrons with acoustical phonons using the extended Hubbard-Holstein model in which both, the electron-phonon interaction and the on-site Coulomb repulsion are considered to be strong. The Lang-Firsov canonical transformation allows to obtain mobile polarons for which a new diagram technique and generalized Wick's theorem is used. This allows to handle the Coulomb repulsion between the electrons emerged into a sea of phonon fields (\textit{phonon clouds}). The physics of emission and absorption of the collective phonon-field mode by the polarons is discussed in detail. Moreover, we have investigated the different behavior of optical and acoustical phonon clouds when propagating through the lattice. In the strong-coupling limit of the electron-phonon interaction, and in the normal as well as in the superconducting phase, chronological thermodynamical averages of products of acoustical phonon-cloud operators can be expressed by one-cloud operator averages. While the normal one-cloud propagator has the form of a Lorentzian, the anomalous one is of Gaussian form and considerably smaller. Therefore, the anomalous electron Green's functions can be considered to be more important than corresponding polarons functions, i.e., pairing of electrons without phonon-clouds is easier to achieve than pairing of polarons with such clouds.Comment: : 28 pages, 9 figures, revtex4. Invited paper for a special issue of Low Temperature Physics dedicated to the 20th anniversary of HTS

Diagrammatic theory for Periodic Anderson Model: Stationary property of the thermodynamic potential

Diagrammatic theory for Periodic Anderson Model has been developed, supposing the Coulomb repulsion of $f-$ localized electrons as a main parameter of the theory. $f-$ electrons are strongly correlated and $c-$ conduction electrons are uncorrelated. Correlation function for $f-$ and mass operator for $c-$ electrons are determined. The Dyson equation for $c-$ and Dyson-type equation for $f-$ electrons are formulated for their propagators. The skeleton diagrams are defined for correlation function and thermodynamic functional. The stationary property of renormalized thermodynamic potential about the variation of the mass operator is established. The result is appropriate as for normal and as for superconducting state of the system.Comment: 12 pages, 10 figure

Orthostasis test in the practice of the cardiologist

The orthostasis test makes it possible to evaluate neurohumoral regulation and reaction of the circulatory system and to detect changes in the function of a number of internal organs (especially the kidney). Simultaneous recording of the ECG in an orthostatic position despite nonspecificity, makes it possible to detect hidden damage (organic or metabolic) or increased sensitivity of the myocardium to stressor sympathetico-adrenal effects, stability of therapeutic effect, and the action mechanism of a number of drugs

Planets of the solar system

Venera and Mariner spacecraft and ground based radio astronomy and spectroscopic observations of the atmosphere and surface of venus are examined. The composition and structural parameters of the atmosphere are discussed as the basis for development of models and theories of the vertical structure of the atmosphere, the greenhouse effect, atmospheric circulation and cloud cover. Recommendations for further meteorological studies are given. Ground based and Pioneer satellite observation data on Jupiter are explored as well as calculations and models of the cloud structure, atmospheric circulation and thermal emission field of Jupiter

Research On Maximizing Critical And Reducing Initial Heat Flux Densities To Eliminate Any Film Boiling And Minimize Distortion During Quenching

In the paper the results of testing three types of FUCHS oils: Thermisol QH 120, Thermisol QH 10 and Thermisol QB 46 are discussed. The main attention is paid to critical heat flux densities evaluation because they create a basis for optimizing cooling intensity of any liquid quenchant. In the paper is underlined that any film boiling during quenching is undesirable since it is a reason for big distortion and non-uniform surface harness. It is shown that intensive quenching decreases distortion of steel parts during quenching. To eliminate film boiling during quenching in mineral oils, optimal temperature of oil should be chosen which maximize the first critical heat flux density and special additives should be used to decrease initial heat flux by creating surface micro-coating. Along with the evaluation of heat transfer coefficients, critical heat flux densities inherent to liquid quenchant must be measured first to optimize quenching processes. International DATABASE on cooling characteristics of liquid quenchants must include critical heat flux densities, initial heat flux densities, and heat transfer coefficients allowing optimizing and governing quenching processes

Diagrammatic theory for Anderson Impurity Model. Stationary property of the thermodynamic potential

A diagrammatic theory around atomic limit is proposed for normal state of Anderson Impurity Model. The new diagram method is based on the ordinary Wick's theorem for conduction electrons and a generalized Wick's theorem for gtrongly correlated impurity electrons. This last theorem coincides with the definition of Kubo cumulants. For the mean value of the evolution operator a linked cluster theorem is proved and a Dyson's type equations for one-particle propagators are established. The main element of these equations is the correlation function which contains the spin, charge and pairing fluctuations of the system. The thermodynamic potential of the system is expressed through one-particle renormalized Green's functions and the corelation function. The stationary property of the thermodynamic potential is established with respect to the changes of correlation function.Comment: 7 pages, 6 figures, Submitted to PR

Strong interaction of correlated electrons with phonons: Exchange of phonon clouds by polarons

We investigate the interaction of strongly correlated electrons with phonons in the frame of the Hubbard-Holstein model. The electron-phonon interaction is considered to be strong and is an important parameter of the model besides the Coulomb repulsion of electrons and band filling. This interaction with the nondispersive optical phonons has been transformed to the problem of mobile polarons by using the canonical transformation of Lang and Firsov. We discuss in particular the case for which the on-site Coulomb repulsion is exactly cancelled by the phonon-mediated attractive interaction and suggest that polarons exchanging phonon clouds can lead to polaron pairing and superconductivity. It is then the frequency of the collective mode of phonon clouds being larger than the bare frequency, which determines the superconducting transition temperature.Comment: 23 pages, Submitted to Phys. Rev.

Energy transfer processes in Er-doped SiO2 sensitized with Si nanocrystals

We present a high-resolution photoluminescence study of Er-doped SiO2 sensitized with Si nanocrystals (Si NCs). Emission bands originating from recombination of excitons confined in Si NCs and of internal transitions within the 4f-electron core of Er3+ ions, and a band centered at lambda = 1200nm have been identified. Their kinetics have been investigated in detail. Based on these measurements, we present a comprehensive model for energy transfer mechanisms responsible for light generation in this system. A unique picture of energy flow between subsystems of Er3+ and Si NCs is developed, yielding truly microscopic information on the sensitization effect and its limitations. In particular, we show that most of the Er3+ ions available in the system are participating in the energy exchange. The long standing problem of apparent loss of optical activity of majority of Er dopants upon sensitization with Si NCs is clarified and assigned to appearance of a very efficient energy exchange mechanism between Si NCs and Er3+ ions. Application potential of SiO2:Er sensitized by Si NCs is discussed in view of the newly acquired microscopic insight.Comment: 30 pages 13 figure