NASA Astrophysics Data System (ADS)
Bauer, Jarosław H.
2016-07-01
A derivation of the ionization rate for a hydrogen atom in its ground state (or a hydrogen-like positive ion) in a strong linearly polarized laser field is presented. The derivation utilizes the famous Keldysh probability amplitude in the length gauge (in the dipole approximation) and without Coulomb effects in the final state of the ionized electron. No further approximations are made, because the amplitude has been expanded in the double Fourier series in a time domain (with the help of the generalized Bessel functions). Thus, our theory has no other limitations that are characteristic of the original Keldysh theory. We compare our ‘exact’ theory with the original Keldysh one by studying photoionization energy spectra and total ionization rates. We show a breakdown of the original Keldysh theory for higher frequencies (when the photon energy approaches the binding energy). We also compare our theory with the analogous result in the velocity gauge. In the barrier-suppression regime, the ‘exact’ Keldysh theory gives results which are close to the well-known empirical formula and close to some other numerical or theoretical results. Numerous comparisons of total ionization rates are limited to photons of energies lower or much lower than the binding energy of the atom.
Keldysh formalism for multiple parallel worlds
NASA Astrophysics Data System (ADS)
Ansari, M.; Nazarov, Y. V.
2016-03-01
We present a compact and self-contained review of the recently developed Keldysh formalism for multiple parallel worlds. The formalism has been applied to consistent quantum evaluation of the flows of informational quantities, in particular, to the evaluation of Renyi and Shannon entropy flows. We start with the formulation of the standard and extended Keldysh techniques in a single world in a form convenient for our presentation. We explain the use of Keldysh contours encompassing multiple parallel worlds. In the end, we briefly summarize the concrete results obtained with the method.
Franz-Keldysh effect in GeSn pin photodetectors
NASA Astrophysics Data System (ADS)
Oehme, M.; Kostecki, K.; Schmid, M.; Kaschel, M.; Gollhofer, M.; Ye, K.; Widmann, D.; Koerner, R.; Bechler, S.; Kasper, E.; Schulze, J.
2014-04-01
The optical properties and the Franz-Keldysh effect at the direct band gap of GeSn alloys with Sn concentrations up to 4.2% at room temperature were investigated. The GeSn material was embedded in the intrinsic region of a Ge heterojunction photodetector on Si substrates. The layer structure was grown by means of ultra-low temperature molecular beam epitaxy. The absorption coefficient as function of photon energy and the direct bandgap energies were determined. In all investigated samples, the Franz-Keldysh effect can be observed. A maximum absorption ratio of 1.5 was determined for 2% Sn for a voltage swing of 3 V.
Femtosecond time-resolved dynamical Franz-Keldysh effect
NASA Astrophysics Data System (ADS)
Otobe, T.; Shinohara, Y.; Sato, S. A.; Yabana, K.
2016-01-01
We theoretically investigate the dynamical Franz-Keldysh effect in femtosecond time resolution, that is, the time-dependent modulation of a dielectric function at around the band gap under an irradiation of an intense laser field. We develop a pump-probe formalism in two distinct approaches: first-principles simulation based on real-time time-dependent density functional theory and analytic consideration of a simple two-band model. We find that, while time-average modulation can be reasonably described by the static Franz-Keldysh theory, a remarkable phase shift is found to appear between the dielectric response and the applied electric field.
Franz-Keldysh effect in GeSn pin photodetectors
Oehme, M. Kostecki, K.; Schmid, M.; Kaschel, M.; Gollhofer, M.; Ye, K.; Widmann, D.; Koerner, R.; Bechler, S.; Kasper, E.; Schulze, J.
2014-04-21
The optical properties and the Franz-Keldysh effect at the direct band gap of GeSn alloys with Sn concentrations up to 4.2% at room temperature were investigated. The GeSn material was embedded in the intrinsic region of a Ge heterojunction photodetector on Si substrates. The layer structure was grown by means of ultra-low temperature molecular beam epitaxy. The absorption coefficient as function of photon energy and the direct bandgap energies were determined. In all investigated samples, the Franz-Keldysh effect can be observed. A maximum absorption ratio of 1.5 was determined for 2% Sn for a voltage swing of 3 V.
Color Glass Condensate in Schwinger–Keldysh QCD
Jeon, Sangyong
2014-01-15
Within the Schwinger–Keldysh representation of many-body QCD, it is shown that the leading quantum corrections to the strong classical color field are “classical” in the sense that the fluctuation field still obeys the classical Jacobi-field equation, while the quantum effects solely reside in the fluctuations of the initial field configurations. Within this context, a systematic derivation of the JIMWLK renormalization group equation is presented. A clear identification of the correct form of gauge transformation rules and the correct form of the matter-field Lagrangian in the Schwinger–Keldysh QCD is also presented. -- Highlights: •Application of the Schwinger–Keldysh formalism to many-body QCD. •Clean separation of classical and quantum degrees of freedom. •Identification of the correct coupling between the gluon field and the color source. •Identification of the correct gauge transformation rules. •Sources of the classicality and quantum corrections to JIMWLK clarified.
Nonequilibrium many-body steady states via Keldysh formalism
NASA Astrophysics Data System (ADS)
Maghrebi, Mohammad F.; Gorshkov, Alexey V.
2016-01-01
Many-body systems with both coherent dynamics and dissipation constitute a rich class of models which are nevertheless much less explored than their dissipationless counterparts. The advent of numerous experimental platforms that simulate such dynamics poses an immediate challenge to systematically understand and classify these models. In particular, nontrivial many-body states emerge as steady states under nonequilibrium dynamics. While these states and their phase transitions have been studied extensively with mean-field theory, the validity of the mean-field approximation has not been systematically investigated. In this paper, we employ a field-theoretic approach based on the Keldysh formalism to study nonequilibrium phases and phase transitions in a variety of models. In all cases, a complete description via the Keldysh formalism indicates a partial or complete failure of the mean-field analysis. Furthermore, we find that an effective temperature emerges as a result of dissipation, and the universal behavior including the dynamics near the steady state is generically described by a thermodynamic universality class.
Attosecond dynamical Franz-Keldysh effect in polycrystalline diamond.
Lucchini, M; Sato, S A; Ludwig, A; Herrmann, J; Volkov, M; Kasmi, L; Shinohara, Y; Yabana, K; Gallmann, L; Keller, U
2016-08-26
Short, intense laser pulses can be used to access the transition regime between classical and quantum optical responses in dielectrics. In this regime, the relative roles of inter- and intraband light-driven electronic transitions remain uncertain. We applied attosecond transient absorption spectroscopy to investigate the interaction between polycrystalline diamond and a few-femtosecond infrared pulse with intensity below the critical intensity of optical breakdown. Ab initio time-dependent density functional theory calculations, in tandem with a two-band parabolic model, accounted for the experimental results in the framework of the dynamical Franz-Keldysh effect and identified infrared induction of intraband currents as the main physical mechanism responsible for the observations. PMID:27563093
Keldysh field theory for driven open quantum systems.
Sieberer, L M; Buchhold, M; Diehl, S
2016-09-01
Recent experimental developments in diverse areas-ranging from cold atomic gases to light-driven semiconductors to microcavity arrays-move systems into the focus which are located on the interface of quantum optics, many-body physics and statistical mechanics. They share in common that coherent and driven-dissipative quantum dynamics occur on an equal footing, creating genuine non-equilibrium scenarios without immediate counterpart in equilibrium condensed matter physics. This concerns both their non-thermal stationary states and their many-body time evolution. It is a challenge to theory to identify novel instances of universal emergent macroscopic phenomena, which are tied unambiguously and in an observable way to the microscopic drive conditions. In this review, we discuss some recent results in this direction. Moreover, we provide a systematic introduction to the open system Keldysh functional integral approach, which is the proper technical tool to accomplish a merger of quantum optics and many-body physics, and leverages the power of modern quantum field theory to driven open quantum systems. PMID:27482736
Keldysh field theory for driven open quantum systems
NASA Astrophysics Data System (ADS)
Sieberer, L. M.; Buchhold, M.; Diehl, S.
2016-09-01
Recent experimental developments in diverse areas—ranging from cold atomic gases to light-driven semiconductors to microcavity arrays—move systems into the focus which are located on the interface of quantum optics, many-body physics and statistical mechanics. They share in common that coherent and driven–dissipative quantum dynamics occur on an equal footing, creating genuine non-equilibrium scenarios without immediate counterpart in equilibrium condensed matter physics. This concerns both their non-thermal stationary states and their many-body time evolution. It is a challenge to theory to identify novel instances of universal emergent macroscopic phenomena, which are tied unambiguously and in an observable way to the microscopic drive conditions. In this review, we discuss some recent results in this direction. Moreover, we provide a systematic introduction to the open system Keldysh functional integral approach, which is the proper technical tool to accomplish a merger of quantum optics and many-body physics, and leverages the power of modern quantum field theory to driven open quantum systems.
Schwinger-Keldysh canonical formalism for electronic Raman scattering
NASA Astrophysics Data System (ADS)
Su, Yuehua
2016-03-01
Inelastic low-energy Raman and high-energy X-ray scatterings have made great progress in instrumentation to investigate the strong electronic correlations in matter. However, theoretical study of the relevant scattering spectrum is still a challenge. In this paper, we present a Schwinger-Keldysh canonical perturbation formalism for the electronic Raman scattering, where all the resonant, non-resonant and mixed responses are considered uniformly. We show how to use this formalism to evaluate the cross section of the electronic Raman scattering off an one-band superconductor. All the two-photon scattering processes from electrons, the non-resonant charge density response, the elastic Rayleigh scattering, the fluorescence, the intrinsic energy-shift Raman scattering and the mixed response, are included. In the mean-field superconducting state, Cooper pairs contribute only to the non-resonant response. All the other responses are dominated by the single-particle excitations and are strongly suppressed due to the opening of the superconducting gap. Our formalism for the electronic Raman scattering can be easily extended to study the high-energy resonant inelastic X-ray scattering.
Studies of Keldysh Scaled Systems with Ultrafast Strong-Field Sources
NASA Astrophysics Data System (ADS)
Szafruga, Urszula; Blaga, Cosmin; Xu, Junliang; Dichiara, Anthony; Link, Emily; Agostini, Pierre; Dimauro, Louis
2015-05-01
Keldysh theory suggests that we can control the multiphoton/tunneling ionization mechanism by choosing appropriate laser parameters and target atoms. The Keldysh parameter values for the noble gases at near-infrared wavelengths (0.8 micron) are similar to those of the alkali metal atoms in strong mid-infrared (3-4 micron) laser fields. By studying atomic species with similar Keldysh parameters and different electronic structures (noble gases vs alkali metals) we aim to expand our understanding of the global, Keldysh invariant, and atom specific ionization features. Further, since alkali metal atoms have a single valence electron they may provide a more appropriate test of theories based off of the single-active-electron approximation. In this work we measured photoelectron spectra and ion yields of Sodium, Potassium and Cesium spanning the range of multiphoton and tunneling ionization regimes. Our findings are discussed in relation to previous results in noble gas/800nm experiments and compared to ADK, SFA and TDSE calculations.
NASA Astrophysics Data System (ADS)
Topcu, Turker; Robicheaux, Francis
2012-06-01
It is common practice in strong-laser physics community that dynamical regime of atomic ionization is described by the Keldysh parameter, γ. Two distinct cases where γ1 and γ1 are associated with ionization mechanisms that are predominantly in tunneling and in multi-photon regimes, respectively. We report on our fully three-dimensional ab initio quantum simulations of ionization of hydrogen atoms in laser fields described in terms of the Keldysh parameter by solving the corresponding time-dependent Schr"odinger equation. We find that the Keldysh parameter is useful in inferring the dynamical ionization regime only when coupled with the scaled laser frequency, φ, when a large range of laser frequencies and peak intensities are considered. The additional parameter φ relates the laser frequency φ to the classical Kepler frequency φK of the electron, and together with the Keldysh parameter, they can be used to refer to an ionization regime.
Excitation spectra of bosons in optical lattices from the Schwinger-Keldysh calculation
Grass, T. D.; Santos, F. E. A. dos; Pelster, A.
2011-07-15
Within the Schwinger-Keldysh formalism we derive a Ginzburg-Landau theory for the Bose-Hubbard model which describes the real-time dynamics of the complex order parameter field. Analyzing the excitations in the vicinity of the quantum phase transition, it turns out that particle-hole dispersions in the Mott phase map continuously onto corresponding amplitude-phase excitations in the superfluid phase, which have been detected recently by Bragg spectroscopy measurements.
Detection of picosecond electrical pulses using the intrinsic Franz{endash}Keldysh effect
Lampin, J. F.; Desplanque, L.; Mollot, F.
2001-06-25
We report time-resolved measurements of ultrafast electrical pulses propagating on a coplanar transmission line using the intrinsic Franz{endash}Keldysh effect. A low-temperature-grown GaAs layer deposited on a GaAs substrate allows generation and also detection of ps pulses via electroabsorption sampling (EAS). This all-optical method does not require any external sampling probe. A typical rise time of 1.1 ps has been measured. EAS is a good candidate for use in THz characterization of ultrafast devices. {copyright} 2001 American Institute of Physics.
Exploring the high-order harmonic generation from Rydberg states with a fixed Keldysh parameter
NASA Astrophysics Data System (ADS)
Ata Bleda, Erdi; Yavuz, Ilhan; Altun, Zikri; Topcu, Turker
2012-06-01
The commonly adopted viewpoint that the Keldysh parameter γ determines the dynamical regime of ionization in strong field physics has long been demonstrated to be a misleading one. One can then ask what happens in strong field ionization as relevant parameters, such as laser intensity and frequency, are varied while keeping γ fixed. We present results from our simulations of high-order harmonic generation (HHG) from Rydberg states of a hydrogen atom. We calculate high harmonic spectra from various initial states with n up to 42, where the laser intensities and the frequencies are scaled from those for n=1 in order to maintain a fixed Keldysh parameter γ<1. We find that as we go up in n for a fixed γ, the position of the cut-off scales as ˜1/n^2 in terms of the cut-off law predicted by the three-step model for n=1. However, a secondary cut-off structure forms below this, which moves to lower harmonics as n is increased. This second cut-off splits the plateau into two regions, one higher in yield and below the second cut-off, and the second with lower yield following it. We further investigate the final n-distributions for some of the interesting cases to elucidate the physical mechanism leading to this structure
[Radionuclides 90Sr and 137Cs in the benthos near the nuclear submarine "Komsomolets"].
Kuznetsov, A P; Shmelev, I P; Demidov, A M; Efimov, B V; Shubko, V M
1999-01-01
We have analyzed the content of radionuclides 90Sr and 137Cs in the benthofauna and deposits near the nuclear submarine "Komsomolets." Analysis was performed on the basis of the materials of the 31st (1993) and 36th (1995) voyages of R/V "Akademik Mstislav Keldysh" in correspondence with the system of monitoring the state of the abiotic and biotic situation near the nuclear submarine "Komsomolets" (Norwegian Sea). Whereas during the 33rd voyage of this vessel (1994) the content of these elements in the benthic animals at stations located close to the submarine somewhat exceeded the background level of radioactivity (Kuznetsov et al., 1996), no such excess was found during the 31st and 36th voyages. Meanwhile, radioactive cobalt (60Co) was found in representatives of three groups of animals during the 31st voyage at two stations located near the submarine. PMID:10188365
Optical Detection of Organic Chemical Biosignatures at Hydrothermal Vents
NASA Technical Reports Server (NTRS)
Conrad, P. G.; Lane, A. L.; Bhartia, R.; Hug, W. H.
2004-01-01
We have developed a non-contact, optical life detection instrument that can detect organic chemical biosignatures in a number of different environments, including dry land, shallow aqueous, deep marine or in ice. Hence, the instrument is appropriate as a biosignature survey tool both for Mars exploration or in situ experiments in an ice-covered ocean such as one might wish to explore on Europa. Here, we report the results we obtained on an expedition aboard the Russian oceanographic vessel Akademik Mstislav Keldysh to hydrothermal vent sites in the Pacific Ocean using our life detection instrument MCDUVE, a multichannel, deep ultraviolet excitation fluorescence detector. MCDUVE detected organic material distribution on rocks near the vent, as well as direct detection of organisms, both microbial and microscopic. We also were able to detect organic material issuing directly from vent chimneys, measure the organic signature of the water column as we ascended, and passively observe the emission of light directly from some vents.
Nannofossils in upper quaternary bottom sediments of back-arc basins in the southwestern Pacific
NASA Astrophysics Data System (ADS)
Dmitrenko, O. B.
2015-05-01
The analysis of calcareous nannoplankton assemblages in bottom sediments sampled during Cruise 21 of the R/V Akademik Mstislav Keldysh in three areas located in back-arc basins of the southwestern Pacific (western Woodlark in the Solomon Sea, Manus in the Bismarck Sea, Central Lau) reveal that they belong to the Emiliania huxleyi Acme Zone, the most detailed one in the Gartner's scale of 1977. The content of coccoliths and their taxonomic composition indicate warm subtropical-tropical conditions. Long cores demonstrate a decrease in species diversity reflecting the transition from the cold late Pleistocene to the Holocene. The changes in species diversity and presence/absence of thermophilic representatives indicate transformation of depositional environments with unstable conditions in the water column and bottom layer, seismic activity, and widely developed processes of sediment redistribution and reworking.
NASA Astrophysics Data System (ADS)
Shevchenko, V. P.; Novigatsky, A. N.; Kopeikin, V. M.; Starodymova, D. P.
2012-04-01
Black carbon (BC) is the most efficient atmospheric particulate species at absorbing visible light, it could have the large potential impact on Arctic climate. The data on the distribution of the BC in atmosphere over the seas of the Russian Arctic are scarce. New data are presented in this work. The distribution of black carbon in the atmosphere in marine boundary layer in the White, Barents and Kara seas has been measured from September 12 to October 7, 2011 during the 59-th cruise of the RV "Akademik Mstislav Keldysh". The method of aethalometry was used. Backwards trajectories of air masses were calculated using NOAA HYSPLIT model (http://www.arl.noaa.gov/ready.html). The highest values of BC concentrations were recorded near port of Arkhangelsk (600-830 ng/cub.m). In the background areas the BC concentrations varied from 10 to 470 ng/cub.m (120 ng/cub.m in average, standard deviation is 110 ng/cub.m, n=45 measurements). These values are at the level of background values for the Russian Arctic seas. The lowest values were recorded after rains and when air masses came from the Central Arctic. Relatively high BC concentrations in the Kara Sea were in air massed arrived from the NW Siberia and in the Barents Sea in air masses arrived from the Arkhangelsk industrial area. Our studies were supported by the Department of the Earth Sciences of the Russian Academy of Sciences (project "Nanoparticles"), Russian-German Otto Schmidt Laboratory and grant NSh-3714.2010.5. The authors are indebted to crew of the RV "Akademik Mstislav Keldysh" for help in the expedition and to Academician A.P. Lisitzin for valuable recommendations.
NASA Astrophysics Data System (ADS)
Allen, Roland
2013-04-01
In our many earlier simulations of the response of materials and molecules to laser pulses, one-electron states were determined by the time-dependent Schr"odinger equation with an instantaneous one-electron Hamiltonian. These states were then used with Ehrenfest's theorem in a semiclassical treatment of the coupled dynamics of electrons and nuclear coordinates. For strongly-correlated materials, however, true nonequilibrium self-energies are required. Here we describe a practical numerical procedure for employing the Kadanoff-Baym/Keldysh equationsfootnotetextSee e.g. A. Stan, N. E. Dahlen, and R. van Leeuwen, J. Chem. Phys. 130, 224101 (2009) and T. Kita, Prog. Theor. Phys. 123, 581 (2010). together with Ehrenfest's theorem, and with conserving self-energies appropriate to correlated materials.
Giraldi, Filippo
2015-09-15
The Schwinger-Keldysh nonequilibrium theory allows the description of various transport phenomena involving bosons (fermions) embedded in bosonic (fermionic) environments. The retarded Green’s function obeys the Dyson equation and determines via its non-vanishing asymptotic behavior the dissipationless open dynamics. The appearance of this regime is conditioned by the existence of the solution of a general class of transcendental equations in complex domain that we study. Particular cases consist in transcendental equations containing exponential, hyperbolic, power law, logarithmic, and special functions. The present analysis provides an analytical description of the thermal and temporal correlation function of two general observables of a quantum system in terms of the corresponding spectral function. Special integral properties of the spectral function guarantee non-vanishing asymptotic behavior of the correlation function.
Keldysh field theory for nonequilibrium condensation in a parametrically pumped polariton system
NASA Astrophysics Data System (ADS)
Dunnett, K.; Szymańska, M. H.
2016-05-01
We develop a quantum field theory for parametrically pumped polaritons using Keldysh Green's function techniques with which the occupations of the excitation spectra can be calculated. By considering the mean field and Gaussian fluctuations, we find that the highly nonequilibrium phase transition to the optical parametric oscillator regime is in some ways similar to equilibrium condensation. In particular, we show that this phase transition can be associated with an effective chemical potential, at which the system's bosonic distribution function diverges, and an effective temperature for low energy modes. As in equilibrium systems, the transition is achieved by tuning this effective chemical potential to the energy of the lowest normal mode. Since the nonequilibrium occupations of the modes are available, we determine experimentally observable properties such as the luminescence and absorption spectra.
An analysis of temperature dependent piezoelectric Franz-Keldysh effect in AlGaN
NASA Astrophysics Data System (ADS)
Hou, Y. T.; Teo, K. L.; Li, M. F.; Uchida, Kazuo; Tokunaga, Hiroki; Akutsu, Nakao; Matsumoto, Koh
2000-02-01
Strong Franz-Keldysh oscillations near the band gap of AlGaN are observed in the contactless electroreflectance (CER) studies of a GaN/InGaN/AlGaN multilayer structure. The line shape analysis of the CER spectra at different temperatures provides an accurate determination of the AlGaN band gap energies and the built-in electric fields. Using the existing data of the thermal expansion coefficients of GaN and sapphire, and the piezoelectric constants of AlGaN, the temperature dependence of the electric field is estimated and is in good agreement with the experimental results between 15 and 300 K. We attribute such electric field to the piezoelectric strain effect.
Franz–Keldysh effect in n-type GaN Schottky barrier diode under high reverse bias voltage
NASA Astrophysics Data System (ADS)
Maeda, Takuya; Okada, Masaya; Ueno, Masaki; Yamamoto, Yoshiyuki; Horita, Masahiro; Suda, Jun
2016-09-01
The photocurrent of GaN vertical Schottky barrier diodes was investigated under sub-bandgap wavelength light irradiation. Under a low reverse bias voltage, the photocurrent is induced by internal photoemission, while under a high reverse bias voltage, the photocurrent increases significantly with the bias voltage. This is due to sub-bandgap optical absorption in a depletion region due to the Franz–Keldysh effect. The voltage and wavelength dependences of the photocurrent are successfully explained quantitatively.
Role of quantum trajectory in high-order harmonic generation in the Keldysh multiphoton regime.
Li, Peng-Cheng; Jiao, Yuan-Xiang; Zhou, Xiao-Xin; Chu, Shih-I
2016-06-27
We present a systematic study of spectral and temporal structure of high-order harmonic generation (HHG) by solving accurately the time-dependent Schrödinger equation for a hydrogen atom in the multiphoton regime where the Keldysh parameter is greater unity. Combining with a time-frequency transform and an extended semiclassical analysis, we explore the role of quantum trajectory in HHG. We find that the time-frequency spectra of the HHG plateau near cutoff exhibit a decrease in intensity associated with the short- and long-trajectories when the ionization process is pushed from the multiphoton regime into the tunneling regime. This implies that the harmonic emission spectra in the region of the HHG plateau near and before the cutoff are suppressed. To see the generality of this prediction, we also present a time-dependent density-functional theoretical study of the effect of correlated multi-electron responses on the spectral and temporal structure of the HHG plateau of the Ar atom. PMID:27410589
Role of quantum trajectory in high-order harmonic generation in the Keldysh multiphoton regime
NASA Astrophysics Data System (ADS)
Li, Peng-Cheng; Chu, Shih-I.
2016-05-01
We present a systematic study of quantum-trajectory analysis of high-order harmonic generation (HHG) by solving accurately the time-dependent Schrödinger equation for a hydrogen atom in the multiphoton regime where the Keldysh parameter is greater unity. We perform the time-frequency transform to explore the spectral characteristics of the HHG. We find that the time-frequency spectra exhibit a broken distribution at above-threshold HHG due to the competition associated with the short- and long-trajectories when the ionization process is pushed from the multiphoton regime into the tunneling regime, it implies that the harmonic emission in the broken regions of time-frequency spectra are suppressed. In addition, we present a time-dependent density-functional theory approach for an ab initio study of the effect of correlated multielectron responses on the harmonic emission of Ar atom associated with the quantum trajectories in the multiphoton regime. This work is partially supported by DOE.
Plimak, L.I.; Stenholm, S.
2012-11-15
The connection between real-time quantum field theory (RTQFT) [see, e.g., A. Kamenev and A. Levchenko, Adv. Phys. 58 (2009) 197] and phase-space techniques [E. Wolf and L. Mandel, Optical Coherence and Quantum Optics (Cambridge, 1995)] is investigated. The Keldysh rotation that forms the basis of RTQFT is shown to be a phase-space mapping of the quantum system based on the symmetric (Weyl) ordering. Following this observation, we define generalised Keldysh rotations based on the class of operator orderings introduced by Cahill and Glauber [K.E. Cahill, R.J. Glauber, Phys. Rev. 177 (1969) 1882]. Each rotation is a phase-space mapping, generalising the corresponding ordering from free to interacting fields. In particular, response transformation [L.I. Plimak, S. Stenholm, Ann. Phys. (N.Y.) 323 (2008) 1989] extends the normal ordering of free-field operators to the time-normal ordering of Heisenberg operators. Structural properties of the response transformation, such as its association with the nonlinear quantum response problem and the related causality properties, hold for all generalised Keldysh rotations. Furthermore, we argue that response transformation is especially suited for RTQFT formulation of spatial, in particular, relativistic, problems, because it extends cancellation of zero-point fluctuations, characteristic of the normal ordering, to interacting fields. As an example, we consider quantised electromagnetic field in the Dirac sea. In the time-normally-ordered representation, dynamics of the field looks essentially classical (fields radiated by currents), without any contribution from zero-point fluctuations. For comparison, we calculate zero-point fluctuations of the interacting electromagnetic field under orderings other than time-normal. The resulting expression is physically inconsistent: it does not obey the Lorentz condition, nor Maxwell's equations. - Highlights: Black-Right-Pointing-Pointer The Keldysh rotation is a phase-space mapping based on
Tunneling time in attosecond experiments, intrinsic-type of time. Keldysh, and Mandelstam–Tamm time
NASA Astrophysics Data System (ADS)
Kullie, Ossama
2016-05-01
Tunneling time in attosecond and strong-field experiments is one of the most controversial issues in current research, because of its importance to the theory of time, the time operator and the time–energy uncertainty relation in quantum mechanics. In Kullie (2015 Phys. Rev. A 92 052118) we derived an estimation of the (real) tunneling time, which shows an excellent agreement with the time measured in attosecond experiments, our derivation is found by utilizing the time–energy uncertainty relation, and it represents a quantum clock. In this work, we show different aspects of the tunneling time in attosecond experiments, we discuss and compare the different views and approaches, which are used to calculate the tunneling time, i.e. Keldysh time (as a real or imaginary quantity), Mandelstam–Tamm time, the classical view of the time measurement and our tunneling time relation(s). We draw some conclusions concerning the validity and the relation between the different types of the tunneling time with the hope that they will help to answer the question put forward by Orlando et al (2014 J. Phys. B 47 204002, 2014 Phys. Rev. A 89 014102): tunneling time, what does it mean? However, as we will see, the important question is a more general one: how to understand the time and the measurement of the time of a quantum system? In respect to our result, the time in quantum mechanics can be, in more general fashion, classified in two types, intrinsic dynamically connected, and external dynamically not connected to the system, and consequently (perhaps only) classical Newtonian time remains as a parametric type of time.
The role of optoelectronic feedback on Franz-Keldysh voltage modulation of transistor lasers
NASA Astrophysics Data System (ADS)
Chang, Chi-Hsiang; Chang, Shu-Wei; Wu, Chao-Hsin
2016-03-01
Possessing both the high-speed characteristics of heterojunction bipolar transistors (HBTs) and enhanced radiative recombination of quantum wells (QWs), the light-emitting transistor (LET) which operates in the regime of spontaneous emissions has achieved up to 4.3 GHz modulation bandwidth. A 40 Gbit/s transmission rate can be even achieved using transistor laser (TL). The transistor laser provides not only the current modulation but also direct voltage-controlled modulation scheme of optical signals via Franz-Keldysh (FK) photon-assisted tunneling effect. In this work, the effect of FK absorption on the voltage modulation of TLs is investigated. In order to analyze the dynamics and optical responses of voltage modulation in TLs, the conventional rate equations relevant to diode lasers (DLs) are first modified to include the FK effect intuitively. The theoretical results of direct-current (DC) and small-signal alternating-current (AC) characteristics of optical responses are both investigated. While the DC characteristics look physical, the intrinsic optical response of TLs under the FK voltage modulation shows an AC enhancement with a 20 dB peak, which however is not observed in experiment. A complete model composed of the intrinsic optical transfer function and an electrical transfer function fed back by optical responses is proposed to explain the behaviors of voltage modulation in TLs. The abnormal AC peak disappears through this optoelectronic feedback. With the electrical response along with FK-included photon-carrier rate equations taken into account, the complete voltage-controlled optical modulation response of TLs is demonstrated.
NASA Astrophysics Data System (ADS)
Plimak, L. I.; Stenholm, S.
2012-11-01
The connection between real-time quantum field theory (RTQFT) [see, e.g., A. Kamenev and A. Levchenko, Adv. Phys. 58 (2009) 197] and phase-space techniques [E. Wolf and L. Mandel, Optical Coherence and Quantum Optics (Cambridge, 1995)] is investigated. The Keldysh rotation that forms the basis of RTQFT is shown to be a phase-space mapping of the quantum system based on the symmetric (Weyl) ordering. Following this observation, we define generalised Keldysh rotations based on the class of operator orderings introduced by Cahill and Glauber [K.E. Cahill, R.J. Glauber, Phys. Rev. 177 (1969) 1882]. Each rotation is a phase-space mapping, generalising the corresponding ordering from free to interacting fields. In particular, response transformation [L.I. Plimak, S. Stenholm, Ann. Phys. (N.Y.) 323 (2008) 1989] extends the normal ordering of free-field operators to the time-normal ordering of Heisenberg operators. Structural properties of the response transformation, such as its association with the nonlinear quantum response problem and the related causality properties, hold for all generalised Keldysh rotations. Furthermore, we argue that response transformation is especially suited for RTQFT formulation of spatial, in particular, relativistic, problems, because it extends cancellation of zero-point fluctuations, characteristic of the normal ordering, to interacting fields. As an example, we consider quantised electromagnetic field in the Dirac sea. In the time-normally-ordered representation, dynamics of the field looks essentially classical (fields radiated by currents), without any contribution from zero-point fluctuations. For comparison, we calculate zero-point fluctuations of the interacting electromagnetic field under orderings other than time-normal. The resulting expression is physically inconsistent: it does not obey the Lorentz condition, nor Maxwell's equations.
NASA Astrophysics Data System (ADS)
de Leeuw, A.-W.; Stoof, H. T. C.; Duine, R. A.
2013-09-01
We consider Bose-Einstein condensation of photons in an optical cavity filled with dye molecules that are excited by laser light. By using the Schwinger-Keldysh formalism we derive a Langevin field equation that describes the dynamics of the photon gas and, in particular, its equilibrium properties and relaxation towards equilibrium. Furthermore we show that the finite lifetime effects of the photons are captured in a single dimensionless damping parameter that depends on the power of the external laser pumping the dye. Finally, as applications of our theory we determine spectral functions and collective modes of the photon gas in both the normal and the Bose-Einstein condensed phases.
Wang, Rui; Jacobs, Paul; Smirl, Arthur L.; Zhao, Hui
2013-06-24
The Dynamic Franz Keldysh Effect (DFKE) is produced and controlled in bulk gallium arsenide by quantum interference without the aid of externally applied fields and is spatially and temporally resolved using ellipsometric pump-probe techniques. The {approx}3 THz internal driving field for the DFKE is a transient space-charge field that is associated with a critically damped coherent plasma oscillation produced by oppositely traveling ballistic electron and hole currents that are injected by two-color quantum interference techniques. The relative phase and polarization of the two pump pulses can be used to control the DFKE.
NASA Astrophysics Data System (ADS)
Wang, Rui; Jacobs, Paul; Zhao, Hui; Smirl, Arthur L.
2013-06-01
The Dynamic Franz Keldysh Effect (DFKE) is produced and controlled in bulk gallium arsenide by quantum interference without the aid of externally applied fields and is spatially and temporally resolved using ellipsometric pump-probe techniques. The ˜3 THz internal driving field for the DFKE is a transient space-charge field that is associated with a critically damped coherent plasma oscillation produced by oppositely traveling ballistic electron and hole currents that are injected by two-color quantum interference techniques. The relative phase and polarization of the two pump pulses can be used to control the DFKE.
Piezoelectric Franz-Keldysh effect in a GaN/InGaN/AlGaN multilayer structure
NASA Astrophysics Data System (ADS)
Hou, Yong T.; Teo, Kie L.; Li, Ming Fu; Uchida, Kazuo; Tokunaga, Hiroki; Akutsu, Nakao; Matsumoto, Koh
1999-11-01
Contactless electroreflectance (CER) of a GaN/InGaN/AlGaN multilayer structure grown on sapphire has been measured in the temperature range of 15K and 450K. Except for the GaN exciton structures, well-defined Franz-Keldysh Oscillations are observed above the AlGaN band gap. An electomodulational model based on complex Airy functions is used to analyze the FKOs line shape. The temperature dependence of transition energies is obtained both for GaN and AlGaN. The magnitude of the built in electric field in AlGaN layer is also determined. The temperature dependence of the electric field is found to be consistent with the variation of thermal strain in the epilayer. It is demonstrated that the built-in electric field can be identified to be due to the piezoelectric effect.
NASA Astrophysics Data System (ADS)
Lee, Sang Jo; Sohn, Chang Won; Jo, Hyun-Jun; Han, Im Sik; Kim, Jong Su; Noh, Sam Kyu; Choi, Hyonkwang; Leem, Jae-Young
2015-09-01
The temperature dependences of the junction electric fields and photovoltage have been investigated for a GaAs p+-i-n+ structure by using photoreflectance (PR) spectroscopy. The electric field strength was examined through three types of Franz-Keldysh oscillation (FKO) analyses; then, the photovoltage was evaluated with respect to temperature in the range from 30 to 300 K. From the PR results, we observed two electric fields that are estimated to originate from two regions of FKOs in undoped GaAs and from the space charge region in highly-doped GaAs. The electric field under illumination decreased with decreasing temperature while the photovoltage obtained from the electric field increased. We also demonstrate that PR spectroscopy is a good method for investigating the photovoltaic effect in solar-cell structures.
NASA Astrophysics Data System (ADS)
Kirchner, Stefan; Munoz, Enrique; Bolech, C. J.
2012-02-01
The non-linear conductance of semiconductor heterostructures and single molecule devices exhibiting Kondo physics has recently attracted attention [1,2]. We address the observed sample-dependence across various systems by considering additional electronic contributions present in the effective low-energy model underlying these experiments. To this end we develop a novel version of the superperturbation theory [3] in terms of dual fermions on the Keldysh contour. We analyze the role of particle hole asymmetry on the transport coefficients. Our approach [4] systematically extends the work of Yamada and Yosida and others to the particle-hole asymmetric Anderson model and reproduce the exactly solvable resonant level model and the special case considered in [5]. It correctly describes the strong coupling physics and is free of internal inconsistencies that would lead to a breakdown of current conservation. [4pt] [1] M. Grobis et al., Phys. Rev. Lett. 100, 246601 (2008).[0pt] [2] G. D. Scott et al., Phys. Rev. B 79, 165413 (2009).[0pt] [3] H. Hafermann et al., EPL 85, 27007 (2009).[0pt] [4] Enrique Munoz, C.J. Bolech, and Stefan Kirchner, submitted (2011).[0pt] [5] K. Yamada, Prog. Theo. Phys. 62, 354 (1979).
NASA Astrophysics Data System (ADS)
Danieli, Ernesto P.; Pastawski, Horacio M.; Álvarez, Gonzalo A.
2005-01-01
We develop the Keldysh formalism for the polarization dynamics of an open spin system. We apply it to the swapping between two qubit states in a model describing an NMR cross-polarization experiment. The environment is a set of interacting spins. For fast fluctuations in the environment, the analytical solution shows effects missed by the secular approximation of the quantum master equation for the density matrix: a frequency decrease depending on the system-environment escape rate and the quantum quadratic short time behavior. Considering full memory of the bath correlations yields a progressive change of the swapping frequency.
Macrobenthos of the southern part of St. Anna trough and the adjacent Kara Sea shelf
NASA Astrophysics Data System (ADS)
Galkin, S. V.; Vedenin, A. A.; Minin, K. V.; Rogacheva, A. V.; Molodtsova, T. N.; Rajskiy, A. K.; Kucheruk, N. V.
2015-07-01
Taxonomic composition and ecological structure of benthic communities of the southern part of St. Anna Trough were investigated during the 54th and 59th cruises of RV Akademik Mstislav Keldysh. Material was collected using Sigsbee trawl at 10 stations arranged in two transects (depth range 57-554 m). It was shown that benthic communities of the western arm of the St. Anna Trough differ considerably from the communities of the eastern arm. The western arm communities develop under the influence of active near-bottom hydrodynamics in conditions of rugged topography and a coarse-grained sediment or hard substrate. The wastern arm of the trough is characterized by the predomination of the soft sediment, smooth topography, and weak currents. In the western arm of the trough the influence of the Barents Sea fauna is traced down to the edge of the internal shelf (about 150 m depth). The community of the eastern arm of the trough situated out from the direct influence of the Barents Sea waters represents a continuation of the Ophiocten sericeum community, typical for external Kara Sea shelf. With increasing depth, Ophiopleura borealis becomes the dominant species of the community. In the greatest explored depths some deep-water High-Arctic species, such as echinoids Pourtalesia jeffreysi, were observed. The major factors determining the distribution of benthic communities in the investigated area are the microrelief pattern, the sediment structure, and near-bottom hydrodynamics.
NASA Astrophysics Data System (ADS)
Zavialov, P. O.; Izhitskiy, A. S.; Osadchiev, A. A.; Pelevin, V. V.; Grabovskiy, A. B.
2015-07-01
We present data of measurements of thermohaline and bio-optical fields in the surface layer of the Kara Sea carried out in September 2012, during the 59th cruise of the R.V Akademik Mstislav Keldysh. Measurements were performed during vessel motion along the expedition route using a pump-through CTD system (temperature and salinity) and UV fluorescent lidar (concentrations of chlorophyll, total suspended matter, and dissolved organic matter) with a high spatial resolution (about 10-100 m). Detailed sea-area distribution maps of the above parameters are presented, frontal zones are detected, T, S diagrams for the surface water layer are constructed, and basic water types are identified. It is shown that Ob-Yenisei freshwater runoff is a main factor affecting properties of the surface layer. In the second part of this paper, a numerical model of the dynamics of continental runoff in the Kara Sea is suggested. Model experiments were carried out under real wind conditions of August-September 2011 (NCAR/NCEP reanalysis); the model was validated on the basis of in situ data collected during the cruise.
NASA Astrophysics Data System (ADS)
Shevchenko, Vladimir P.; Kopeikin, Vladimir M.; Evangeliou, Nikolaos; Novigatsky, Alexander N.; Pankratova, Natalia V.; Starodymova, Dina P.; Stohl, Andreas; Thompson, Rona
2016-04-01
Black carbon (BC) particles are highly efficient at absorbing visible light, which has a large potential impact on Arctic climate. However, measurement data on the distribution of BC in the atmosphere over the North Atlantic and the Russian Arctic Seas are scarce. We present measurement data on the distribution of atmospheric BC in the marine boundary layer of the North Atlantic and Baltic, North, Norwegian, Barents, White, Kara and Laptev Seas from research cruises during July 23 to October 6, 2015. During the 62nd and 63rd cruises of the RV "Akademik Mstislav Keldysh" air was filtered through Hahnemuhle fineart quarz-microfibre filters. The mass of BC on the filter was determined by measurement of the attenuation of a beam of light transmitted through the filter. Source areas were estimated by backwards trajectories of air masses calculated using NOAA's HYSPLIT model (http://www.arl.noaa.gov/ready.html) and FLEXPART model (http://www.flexpart.eu). During some parts of the cruises, air masses arrived from background areas of high latitudes, and the measured BC concentrations were low. During other parts of the cruise, air masses arrived from industrially developed areas with strong BC sources, and this led to substantially enhanced measured BC concentrations. Model-supported analyses are currently performed to use the measurement data for constraining the emission strength in these areas.
On Suspended matter grain size in Baltic sea
NASA Astrophysics Data System (ADS)
Bubnova, Ekaterina; Sivkov, Vadim; Zubarevich, Victor
2016-04-01
Suspended matter grain size data were gathered during the 25th research vessel "Akademik Mstislav Keldysh" cruise (1991, September-October). Initial quantitative data were obtained with a use of the Coulter counter and subsequently modified into volume concentrations (mm3/l) for size intervals. More than 80 samples from 15 stations were analyzed (depth range 0-355 m). The main goal of research was to illustrate the spatial variability of suspended matter concentration and dispersion in Baltic Sea. The mutual feature of suspended matter grain size distribution is the logical rise of particle number along with descending of particle's size. Vertical variability of grain size distribution was defined by Baltic Sea hydrological structure, including upper mixed layer - from the surface to the thermocline - with 35 m thick, cold intermediate layer - from the thermocline to the halocline- and bottom layer, which lied under the halocline. Upper layer showed a rise in total suspended matter concentration (up to 0.6 mm3/l), while cold intermediate level consisted of far more clear water (up to 0.1 mm3/l). Such a difference is caused by the thermocline boarding role. Meanwhile, deep bottom water experienced surges in suspended matter concentration owing to the nepheloid layer presence and "liquid bottom" effect. Coastal waters appeared to have the highest amount of particles (up to 5.0 mm3/l). Suspended matter grain size distribution in the upper mixed layer revealed a peak of concentration at 7 μ, which can be due to autumn plankton bloom. Another feature in suspended matter grain size distribution appeared at the deep layer below halocline, where both O2 and H2S were observed and red/ox barrier is. The simultaneous presence of Fe and Mn (in solutions below red/ox barrier) and O2 leads to precipitation of oxyhydrates Fe and Mn and grain size distribution graph peaking at 4.5 μ.
NASA Astrophysics Data System (ADS)
Paropkari, Anil L.; Ray, Durbar; Balaram, V.; Surya Prakash, L.; Mirza, Imran H.; Satyanarayana, M.; Gnaneshwar Rao, T.; Kaisary, Sujata
2010-04-01
An inactive hydrothermal field was discovered near Kings Triple Junction (KTJ) in northern Lau back-arc basin during 19th cruise of R/V Akademik Mstislav Keldysh in 1990. The field consisted of a large elongated basal platform 'the pedestal' with several 'small' chimneys on its periphery and one 'main mound' superposed over it. The surrounding region is carpeted with lava pillows having ferromanganese 'precipitate' as infillings. The adjoining second field consisted of small chimney like growths termed as 'Christmas Tree' Field. The basal pedestal, the peripheral chimneys and small 'Christmas Tree' like growths (samples collected by MIR submersibles), though parts of the same hydrothermal field, differ significantly in their mineralogy and elemental composition indicating different history of formation. The pedestal slab consisting of chalcopyrite and pyrite as major minerals and rich in Cu is likely to have formed at higher temperatures than sphalerite dominated peripheral chimney. Extremely low concentration of high field strength elements (e.g. Zr, Hf, Nb and Ta) and enrichment of light REE in these sulfides indicate prominent influence of aqueous arc-magma, rich in subduction components. The oxide growths in the 'Christmas Tree' Field have two distinct layers, Fe rich orange-red basal part which seems to have formed at very low temperature as precipitates from diffused hydrothermal flows from the seafloor whereas Mn rich black surface coating is formed from hydrothermal fluids emanated from the seafloor during another episode of hydrothermal activity. Perhaps this is for the first time such unique hydrothermal oxide growths are being reported in association with hydrothermal system. Here, we discuss the possible processes responsible for the formation of these different hydrothermal deposits based on their mineralogy and geochemistry.
NASA Astrophysics Data System (ADS)
Stepanjants, Sofia D.
2013-02-01
A report is given about Hydrozoa collected at depths between 455 and 3666 m in the Sea of Japan during the Russian-German expedition on R/V Akademik M.A. Lavrentyev. Ten species were found, with four of them being typical bathyal-abyssal and abyssal zones. A new species, Opercularella angelikae, is described, and it was the dominant hydroid in samples from 970 to 3660 m. Four eurybathic species characteristics of the Sea of Japan were sampled between 455 and 582 m. Abyssal (pseudoabyssal after Andriashev, 1979) hydroid fauna in the Sea of Japan is reported. The hypothesis that an exclusively deep-water fauna is lacking in abyssal regions of the Sea of Japan is disputed. The author's personal opinion considered concerning the borders of 1000 m between shallow and deep hydrozoan species in the Sea of Japan.
Chipman, D.W.; Takahashi, Taro; Rubin, S.; Sutherland, S.C.; Koshlyakov, M.H.; Kozyr, A. |
1997-07-01
This data documentation discusses the procedures and methods used to measure total carbon dioxide (TCO{sub 2}) and partial pressure of CO{sub 2} (pCO{sub 2}) in discrete water samples during the Research Vessel (R/V) Akademik Ioffe Expedition in the South Pacific Ocean. Conducted as part of the World Ocean Circulation Experiment (WOCE), the cruise began in Montevideo, Uruguay, on February 14, 1992, and ended in Wellington, New Zealand, on April 6, 1992. WOCE Section S4P, located along {approximately}67{degree}S between 73{degree}W and 172{degree}E, was completed during the 51-day expedition. One hundred and thirteen hydrographic stations were occupied. Hydrographic and chemical measurements made along WOCE Section S4P included pressure, temperature, salinity, and oxygen measured by a conductivity, temperature, and depth sensor; bottle salinity; bottle oxygen, phosphate; nitrate; nitrite; silicate, TCO{sub 2}; and pCO{sub 2} measured at 4 C.
NASA Astrophysics Data System (ADS)
Skorokhod, Andrey; Belikov, Igor; Pankratova, Natalia; Novigatsky, Alexander; Thompson, Rona
2016-04-01
Atmospheric methane (CH4) is the second most important long-lived greenhouse gas. The Arctic has significant sources of CH4, such as from wetlands and possibly also from methane hydrates, which may act as a positive feedback on the climate system. Despite significant efforts in establishing a network of ground-based CH4 observations in the Arctic zone, there is still a lack of measurements over the Arctic Ocean and sub-polar seas. From 21 July to 9 October 2015, concentrations of CH4 and CO2, as well as of the 13C:12C isotopic ratio in CH4, i.e., δ13C, were measured in the marine boundary layer from aboard the Research Vessel "Akademik Mstislav Keldysh" by the Shirshov Institute of Oceanology. Measurements were made using a Cavity Ring Down Spectroscopy instrument from Picarro™ (model G2132-i). The cruises covered a vast area including the North Atlantic up to 70°N, the Baltic, North, Norwegian, Greenland, Barents, White, Kara and Laptev Seas. To the best of our knowledge, these are the first measurements of their type made in these regions. Concentrations of CH4 typically had low variations (in the range of a few ppb) in the open sea but relatively large variations (of the order of 100 ppb) were recorded near and during stops in ports. High variability of atmospheric CH4 was also registered near the delta of the Lena River in the Laptev Sea, which has been suggested to be a large CH4 reservoir and where bubbles rising through the water column have been observed. The obtained set of δ13CCH4 is characterized by significant range of the measured values varying from open Atlantic to polluted regions near large sea ports. The Keeling plot analyses were implemented to study possible CH4 sources according to its isotopic signature. Footprint analyses are presented for the shipboard observations, as well as comparisons to simulated CH4 concentrations and δ13C using the Lagrangian transport model, FLEXPART. This work has been carried-out with the financial support of
A tribute to Peter A. Rona: A Russian Perspective
NASA Astrophysics Data System (ADS)
Sagalevich, Anatoly; Lutz, Richard A.
2015-11-01
In July 1985 Peter Rona led a cruise of the National Oceanic and Atmospheric Administration (NOAA) ship Researcher as part of the NOAA Vents Program and discovered, for the first time, black smokers, massive sulfide deposits and vent biota in the Atlantic Ocean. The site of the venting phenomena was the Trans-Atlantic Geotraverse (TAG) Hydrothermal Field on the east wall of the rift valley of the Mid-Atlantic Ridge at 26°08‧N; 44°50‧W (Rona, 1985; Rona et al., 1986). In 1986, Peter and an international research team carried out multidisciplnary investigations of both active and inactive hydrothermal zones of the TAG field using the R/V Atlantis and DSV Alvin, discovering two new species of shrimp (Rimicaris exoculata and Chorocaris chacei) (Williams and Rona, 1986) and a hexagonal-shaped form (Paleodictyon nodosum) thought to be extinct (Rona et al., 2009). In 1991 a Russian crew aboard the R/V Akademik Mstislav Keldysh, with two deep-diving, human-occupied submersibles (Mir-1 and Mir-2) (Fig. 1), had the honor of having Peter Rona and a Canadian IMAX film crew from the Stephen Low Company on board to visit the TAG hydrothermal vent field. This was the first of many deep-sea interactions between Russian deep-sea scientists and their colleagues from both the U.S. and Canada. This expedition to the TAG site was part of a major Russian undersea program aimed at exploring extreme deep-sea environments; between 1988 and 2005, the Mir submersibles visited hydrothermal vents and cold seep areas in 20 deep-sea regions throughout the world's oceans (Sagalevich, 2002). Images of several of these areas (the TAG, Snake Pit, Lost City and 9°50‧N vent fields) were obtained using an IMAX camera system emplaced for the first time within the spheres of the Mir submersibles and DSV Alvin in conjunction with the filming of science documentaries (e.g., "Volcanoes of the Deep Sea") produced by the Stephen Low Company in conjunction with Emory Kristof of National Geographic and
NASA Astrophysics Data System (ADS)
Pimenov, Nikolay; Kanapatskiy, Timur; Sivkov, Vadim; Toshchakov, Stepan; Korzhenkov, Aleksei; Ulyanova, Marina
2016-04-01
Comparison of the biogeochemical and microbial features was done for the gas-bearing and background sediments as well as near-bottom water of the Gdansk Deep, The Baltic Sea. Data were received in October, 2015 during 64th cruise of the R/V Akademik Mstislav Keldysh. Gas-bearing sediments were sampled within the known pockmark (Gas-Point, depth 94 m). Background sediments area (BG-Point, depth 86 m) was located several km off the pockmark area. The sulphate concentration in the pore water of the surface sediment layer (0-5 cm) of Gas-Point was 9,7 mmol/l, and sharply decreased with depth (did not exceed 1 mmol/l deeper than 50 cm). The sulphate concentration decrease at BG-Point also took place but was not so considerable. Sulphate concentration decrease is typical for the organic rich sediments of the high productive areas, both as for the methane seep areas. Fast sulphate depletion occurs due to active processes of its microbial reduction by consortium of the sulphate-reduction bacteria, which may use low-molecular organic compounds or hydrogen, formed at the different stages of the organic matter destruction; as well as within the process of the anaerobic methane oxidation by consortium of the methane-trophic archaea and sulphate-reduction bacteria. Together with sulphate concentration decrease the methane content increase, typical for the marine sediments, occurred. At the Gas-Point the methane concentration varied within 10 μmol/dm3 in the surface layer till its maximum at sediment horizon of 65 cm (5 mmol/dm3), and decreased to 1.5 mmol/dm3 at depth of 300 cm. The BG-Point maximum values were defined at sediment horizon 6 cm (2,6 μmol/dm3). Methane sulfate transition zone at the Gas-Point sediments was at 25-35 cm depth; whereas it was not defined at the BG-Point mud. High methane concentration in the gas-bearing sediments results in the formation of the methane seep from the sediments to the near-bottom water. So the Gas-Point near-bottom waters were
NASA Astrophysics Data System (ADS)
Sushkevich, T. A.
2011-09-01
This review is to recall to scientists of the older generation about some historical pages of our memory and about many famous researchers, teachers and colleagues. As to the younger researchers and foreign colleagues, it will be useful for them to get to know about pioneer advancements of the Soviet scientists in the field of information and mathematical supply for cosmonautic problems on the eve of the space era. Main attention is paid down to the scientific experiments conducted on the piloted space vehicles and the research collectives who created the information and mathematical tools for the first space projects. The role of Mstislav Vsevolodovich Keldysh, the Major Theoretician of cosmonautics, is in particular emphasized, who determined in the most degree the basic directions of development of space research and remote sensing of the Earth and planets that are shortly called as REMOTE SENSING.
NASA Astrophysics Data System (ADS)
Osadchiev, Alexander; Zavialov, Peter; Izhitskiy, Alexander; Polukhin, Alexander; Pelevin, Vadim; Makkaveev, Petr; Toktamysova, Zhamal
2015-04-01
The Kara Sea is significantly affected by continental runoff annually receiving about 1350 km3 of river waters. More than 70% of this volume is discharged from Ob and Yenisei gulfs in June - September and forms a buoyant plume that occupies up to 40% of the Kara Sea area. This work is focused on the structure of the upper layer of the southern part of the Kara Sea in September, 2011 which was dominated by large freshwater discharge. The research is based on the statistical analysis of in situ data collected during the 59th cruise of the R/V "Academician Mstislav Keldysh" along the ship track using a pump-through system (temperature, salinity, pH) and ultraviolet fluorescent lidar (concentrations of chlorophyll, total suspended matter and colored dissolved organic matter) with high space resolution (about 100 m). We performed principal component analysis of the large dataset to identify the areas where the considered water parameters can regard as passive tracers of river discharge. Proximity of discharge volumes of Ob and Yenisei rivers together with difference in their thermohaline and chemical properties relatively big distance between Ob and Yenisei gulfs (about 200 km) result in strong nonuniformity of the freshened plume. The subsequent cluster analysis identified spatial characteristics of different water masses within the studied river plume formed by two sources of freshwater discharge.
NASA Astrophysics Data System (ADS)
Mahfouzi, Farzad; Kioussis, Nicholas
Gilbert damping in metallic ferromagnets is mainly governed by the exchange coupling between the electrons and the magnetic degree of freedom, where the time dependent evolution of the magnetization leads to the excitation of electrons and loss of energy as a result of flow of spin and charge currents. However, it turns out that when the magnetization evolves slowly in time, in the presence of spin-orbit interaction (SOI), the resonant electronic excitations has a major contribution to the damping which leads to infinite result in ballistic regime. In this work we consider the inelastic spin-flip scattering of electrons from the magnetic moments and show that in the presence of SOI it leads to the relaxation of the excited electrons. We show that in the case of clean crystal systems such scattering leads to a linear dependence of the Gilbert on the SOI strength and in the limit of diffusive systems we get the Gilbert damping expression obtained from Kambersky's Fermi breathing approach. This research was supported by NSF-PREM Grant No. DMR-1205734
The contribution and spatial distribution of Ob and Yenisei runoff on surface layer of the Kara Sea.
NASA Astrophysics Data System (ADS)
Polukhin, A.; Makkaveev, P.
2012-04-01
On degree of influence of river runoff on water area of the Kara Sea in general it is possible to consider as uniform estuary of two largest Siberian rivers - Ob and Yenisei. The Kara Sea has 41 % of all river runoff from a land in Arctic ocean or 56 % of a river runoff of the rivers of the Siberian sector of Arctic regions. From them of 37 % belong to waters from The Obskaya Guba (the Ob, the Taz, the Pur) and 46 % to waters of Yenisei. Spatial distribution of a river flow and its interaction with sea waters is in many respects defines various and changeable hydrometeorological conditions of the Kara Sea. Hydrochemical researches of the Kara Sea were included into the works of complex expedition in 59th cruise of R/V "Academic Mstislav Keldysh" (on September, 11th - on October, 7th, 2011). This data supplements results of expeditions of Institute of oceanology RAS to the Kara Sea in the autumn 1993 and 2007. In these cruises were met and described lenses of fresh water contained Ob and Yenisei waters defined on hydrochemical parameters. Difference of the data of 2011 from last years is that sampling for researches of distribution of river flow (on silicon, and the general alkalinity) was spent in flowing system from horizon of 1-1,5 m on a course of a vessel with high frequency of sampling. Such technique of sampling allows to investigate a surface water area with high discretness which plays the main role in definition of the contribution of waters of Ob and Yenisei in surface water layer of the Kara Sea. The analysis of the data shows that the area of distribution and the relative contribution of waters of a different origin considerably changes from year to year. It is connected with considerable interannual variability of hydrometeorological conditions and in particular with the general circulation of waters of the Kara Sea. River flow distribution on the surface of the Kara Sea is difficult enough. Nevertheless, distinctions in a chemical compound of waters
Iceberg ploughmark features on bottom surface of the South-Eastern Baltic Sea
NASA Astrophysics Data System (ADS)
Dorokhov, Dmitry; Sivkov, Vadim; Dorokhova, Evgenia; Krechik, Viktor
2016-04-01
A detail swath bathymetry, side-scan sonar and acoustic profiling combined with sediment sampling during the 64th cruise of RV "Academic Mstislav Keldysh" (October 2015) allowed to identify new geomorphological features of the South-Eastern Baltic Sea bottom surface. The extended chaotic ploughmarks (furrows) in most cases filled with thin layer of mud were discovered on surface of the Gdansk-Gotland sill glacial deposits. They are observed on the depth of more than 70 m and have depth and width from 1 to 10 m. Most of them are v- or u-shaped stepped depressions. The side-scan records of similar geomorpholoical features are extensively reported from Northern Hemisphere and Antarctica (Goodwin et al., 1985; Dowdeswell et al., 1993). Ploughmarks are attributed to the action of icebergs scouring into the sediment as they touch bottom. We are suggest that furrows discovered in the South-Eastern Baltic Sea are also the result of iceberg scouring during the Baltic Ice Lake stage (more than 11 600 cal yr BP (Bjorck, 2008)). This assumption confirmed by occurrence of fragmental stones and boulders on the sea bottom surface which are good indicators of iceberg rafting (Lisitzin, 2003). Ice ploughmarks at sea bottom surface were not occurred before in the South-Eastern Baltic Sea. The study was financed by Russian Scientific Fund, grant number 14-37-00047. References Bjorck S. The late Quaternary development of the Baltic Sea Basin. In: The BACC Author Team (eds) Assessment of climate change for the Baltic Sea Basin. Springer, Berlin, Heidelberg. 2008. Dowdeswell J. A., Villinger H., Whittington R. J., Marienfeld P. Iceberg scouring in Scoresby Sund and on the East Greenland continental shelf // Marine Geology. V. 111. N. 1-2. 1993. P. 37-53. Goodwin C. R., Finley J. C., Howard L. M. Ice scour bibliography. Environmental Studies Revolving Funds Report No. 010. Ottawa. 1985. 99 pp. Lisitzin A. P. Sea-Ice and Iceberg Sedimentation in the Ocean: Recent and Past. Springer
Pimenov, N V; Savvichev, A S; Rusanov, I I; Lein, A Iu; Ivanov, M V
2000-01-01
Functioning of microbial communities in surface sediments of the Haakon Mosby underwater mud volcano (lat. 72 degrees N) and in gas seepage fields of the Vestnesa Ridge was investigated using Mir-1 and Mir-2 deep-sea submersibles during the 40th expedition of the research vessel Academician Mstislav Keldysh. Large areas of sedimentary deposits of the Haakon Mosby mud volcano (HMMV) and pockmarks of the Vestnesa Ridge (VR) are covered with bacterial mats 0.1 to 0.5 cm thick. The microbial community making up bacterial mats of the HMMV was predominated by large filamentous bacteria with filaments measuring up to 100 microns in length and 2 to 8 microns in width. The occurrence of rosettes allowed the observed filamentous bacteria to be referred to the morphologically similar genera Leucothrix or Thiothrix. Three morphological types of filamentous bacteria were identified in bacterial mats covering VR pockmarks. Filaments of type one are morphologically similar with representatives of the genera Thioploca or Desmanthos. Type two filaments had numerous inclusions of sulfur and resembled representatives of the genus Thiothrix. The third morphological type was constituted by single filaments made up of tightly connected disk-like cells and can, apparently, be assigned to the genus Beggiatoa. The rates of methane oxidation (up to 1570 microliters C/(dm3 day)) and sulfate reduction (up to 17 mg S/(dm3 day)) measured in surface sediments of HMMV and VR were close to the maximum rates of these processes observed in badly polluted regions of the northwestern shelf of the Black Sea. High rates of microbiological processes correlated with the high number of bacteria. The rate of methane production in sediments studied was notably lower and ranged from 0.1 to 3.5 microliters CH4/(dm3 day). Large areas of the HMMV caldera were populated by pogonophoras, represented by the two species, Sclerolinum sp. and Oligobrachia sp. The mass development of Sclerolinum sp. in the HMMV caldera
NASA Astrophysics Data System (ADS)
Pol'kin, Viktor V.; Sakerin, Sergey M.; Pol'kin, Vasily V.; Turchinovich, Ury S.; Terpugova, Swetlana A.; Tikhomirov, Aleksey B.; Radionov, Vladimir F.
2015-11-01
Latitudinal dependences of aerosol microphysical characteristics are analyzed. The data were obtained in the Russian Antarctic Expedition (RAE) onboard the expedition vessels "Akademik Fedorov" and "Akademik Treshnikov" in 2006- 2014, as well as the research vessel "Akademik Sergey Vavilov" in 2004.
ERIC Educational Resources Information Center
Aydin, Betül; Sari, Serkan Volkan; Sahin, Mustafa
2014-01-01
In this study, examining the relationship of parental acceptance/involvement to self-esteem, hope and academic achievement besides, mediating role of hope on the relationship between perception of parental acceptance/involvement, self esteem and academic achievement were aimed. The study was carried out with 297 students from different…
ERIC Educational Resources Information Center
Yurt, Eyüp; Polat, Seyat
2015-01-01
The purpose of this study was to examine the effectiveness of multiple intelligence applications on academic achievement in Turkey. Accordingly, findings of independent research studies aimed to find out effectiveness of multiple intelligence applications are gathered in a meta-analysis. Total of 71 studies, 66 dissertations and 7 articles were…
Nonlinear phenomena and multiphonon transitions in the exciton region of a spectrum
NASA Astrophysics Data System (ADS)
Lisitsa, M. P.; Taratuta, R. A.; Yaremko, A. M.
1990-08-01
Using the Keldysh diagram method, the nonlinear susceptibility for a Frenkel exciton with account for the multiquantum transitions is obtained. Propagation of the strong resonance electromagnetic wave through the crystal and the optical bistability phenomenon are considered.
Data on conducting the SAMEX-76 experiment
NASA Technical Reports Server (NTRS)
1978-01-01
The compilation of data on conducting the SAMEX-76 experiment is reported. This report includes many tables and graphs of the aircraft's flights and its measurements. Also given is the operation time of this equipment and the many observations that have been made by the Scientific Research Ship Akademik Korolev.
NASA Astrophysics Data System (ADS)
Nemirovskaya, I. A.; Lisitzin, A. P.; Kravchishina, M. D.; Redzhepova, Z. Yu.
2015-10-01
Particulate matter and organic compounds (chlorophyll, lipids, and hydrocarbons) were analyzed in surface waters along the routes of R/Vs Akademik Fedorov (cruise 32) and Akademik Treshnikov (cruise 2) in February-May of 2012 and 2014, respectively, in the course of the 57th and 59th Russian Antarctic expeditions. It was found that the frontal zones exert the primary influence on the concentrations of the mentioned components in the Southern Ocean and in the western part of the Atlantic Ocean. The supply of pollutants into the Eastern Atlantic Ocean on the shelf of the Iberian peninsula results in a pronounced increase in the concentrations of lipids and hydrocarbons causing local anthropogenic pollution zones.
Doppler selection of HF radiosignals on long paths
NASA Astrophysics Data System (ADS)
Zalizovskii, A. V.; Galushko, V. G.; Kashcheev, A. S.; Koloskov, A. V.; Yampolski, Yu. M.; Egorov, I. B.; Popov, A. V.
2007-10-01
The long-term registration of the Doppler spectra of HF radiosignals has been performed on the Moscow-Akademik Vernadsky Ukrainian Antarctic station path. It has been revealed that the spectra are split when the solar terminator crosses direct and return radio lines. The spectral and energy characteristics of direct and return signals have been calculated within the scope of the asymptotic theory of long-range propagation of decametric radiowaves.
Full counting statistics of energy fluctuations in a driven quantum resonator
Clerk, A. A.
2011-10-15
We consider the statistics of time-integrated energy fluctuations of a driven bosonic single-mode resonator, as measured by a quantum nondemolition (QND) detector, using the standard Keldysh prescription to define higher moments. We find that, due to an effective cascading of fluctuations, these statistics are surprisingly nonclassical: the low-temperature, quantum probability distribution is not equivalent to the high-temperature classical distribution evaluated at some effective temperature. Moreover, for a sufficiently large drive detuning and low temperatures, the Keldysh-ordered quasiprobability distribution characterizing these fluctuations fails to be positive-definite; this is similar to the full counting statistics of charge in superconducting systems. We argue that this indicates a kind of nonclassical behavior akin to that tested by Leggett-Garg inequalities.
Multilayer Black Phosphorus as a Versatile Mid-Infrared Electro-optic Material.
Lin, Charles; Grassi, Roberto; Low, Tony; Helmy, Amr S
2016-03-01
We investigate the electro-optic properties of black phosphorus (BP) thin films for optical modulation in the mid-infrared frequencies. Our calculation indicates that an applied out-of-plane electric field may lead to red-, blue-, or bidirectional shift in BP's absorption edge. This is due to the interplay between the field-induced quantum-confined Franz-Keldysh effect and the Pauli-blocked Burstein-Moss shift. The relative contribution of the two electro-absorption mechanisms depends on doping range, operating wavelength, and BP film thickness. For proof-of concept, simple modulator configuration with BP overlaid over a silicon nanowire is studied. Simulation results show that operating BP in the quantum-confined Franz-Keldysh regime can improve the maximal attainable absorption as well as power efficiency compared to its graphene counterpart. PMID:26901350
Multilayer Black Phosphorus as a Versatile Mid-Infrared Electro-optic Material
NASA Astrophysics Data System (ADS)
Lin, Charles; Grassi, Roberto; Low, Tony; Helmy, Amr S.
2016-03-01
We investigate the electro-optic properties of black phosphorus (BP) thin films for optical modulation in the mid-infrared frequencies. Our calculation indicates that an applied out-of-plane electric field may lead to red-, blue-, or bidirectional shift in BP's absorption edge. This is due to the interplay between the field-induced quantum-confined Franz-Keldysh effect and the Pauli-blocked Burstein-Moss shift. The relative contribution of the two electro-absorption mechanisms depends on doping range, operating wavelength, and BP film thickness. For proof-of concept, simple modulator configuration with BP overlaid over a silicon nanowire is studied. Simulation result shows that operating BP in the quantum-confined Franz-Keldysh regime can enable improved maximal attainable absorption as well as power efficiency compared to its graphene counterpart.
NASA Astrophysics Data System (ADS)
Kumazaki, Yusuke; Yatabe, Zenji; Sato, Taketomo
2016-04-01
We aimed to develop a photoassisted electrochemical etching process for the formation of GaN porous structures. Pore linearity and depth controllability were strongly affected by the anode voltage. In addition, the use of light with an energy below the band gap played an important role in controlling the pore diameter. Spectro-electrochemical measurements revealed that the high electric field induced at the GaN/electrolyte interface caused a redshift of the photoabsorption edge. This specific phenomenon can be explained by a theoretical calculation based on the Franz-Keldysh effect. On the basis of the results of our experimental and theoretical analyze, we propose a formation model for GaN porous structures. We also note that the application of the Franz-Keldysh effect is useful in controlling the structural properties of GaN porous structures.
A theoretical analysis of the current-voltage characteristics of solar cells
NASA Technical Reports Server (NTRS)
Fang, R. C. Y.; Hauser, J. R.
1979-01-01
The following topics are discussed: (1) dark current-voltage characteristics of solar cells; (2) high efficiency silicon solar cells; (3) short circuit current density as a function of temperature and the radiation intensity; (4) Keldysh-Franz effects and silicon solar cells; (5) thin silicon solar cells; (6) optimum solar cell designs for concentrated sunlight; (7) nonuniform illumination effects of a solar cell; and (8) high-low junction emitter solar cells.
Spin projection chromatography
NASA Astrophysics Data System (ADS)
Danieli, E. P.; Pastawski, H. M.; Levstein, P. R.
2004-01-01
We formulate the many-body spin dynamics at high temperature within the non-equilibrium Keldysh formalism. For the simplest XY interaction, analytical expressions in terms of the one particle solutions are obtained for linear and ring configurations. For small rings of even spin number, the group velocities of excitations depend on the parity of the total spin projection. This should enable a dynamical filtering of spin projections with a given parity i.e., a spin projection chromatography.
Orbital-resolved strong-field single ionization of acetylene
NASA Astrophysics Data System (ADS)
Ji, Qinying; Cui, Sen; You, Xinyuan; Gong, Xiaochun; Song, Qiying; Lin, Kang; Pan, Haifeng; Ding, Jingxin; Zeng, Heping; He, Feng; Wu, Jian
2015-10-01
We resolve the strong-field single ionization of acetylene into different channels by differentially normalizing the lateral momenta of the directly escaped electrons from the aligned and antialigned molecules. Distinct electron momentum distributions for different channels are observed using both near-infrared and ultraviolet femtosecond laser pulses with Keldysh parameters close to 1. The results are interpreted as a signature of multiple ionization orbitals.
NASA Astrophysics Data System (ADS)
Arrachea, Liliana
2007-01-01
We present an efficient method and a fast algorithm to exactly calculate spectral functions and one-body observables of open quantum systems described by lattice Hamiltonians with harmonically time-dependent terms and without many-body interactions. The theoretical treatment is based in Keldysh nonequilibrium Green’s function formalism. We illustrate the implementation of the technique in a paradigmatic model of a quantum pump driven by local fields oscillating in time with one and two harmonic components.
Non-equilibrium Green functions method in the problem of optical nonlinearities
NASA Astrophysics Data System (ADS)
Lisitsa, M. P.; Yaremko, A. M.; Taratuta, R. A.
1994-01-01
The influence of high power resonance electromagnetic radiation on a Frenkel exciton system is studied. By means of the Keldysh diagram technique a formula for the nonlinear susceptibility is obtained. The influence of the excitation intensity on the shape of exciton band and on the value of the absorption coefficient is established. The phenomena of optical bistability and multistability are considered taking into account the nonlinear boundary conditions.
Topological sigma models & dissipative hydrodynamics
NASA Astrophysics Data System (ADS)
Haehl, Felix M.; Loganayagam, R.; Rangamani, Mukund
2016-04-01
We outline a universal Schwinger-Keldysh effective theory which describes macroscopic thermal fluctuations of a relativistic field theory. The basic ingredients of our construction are three: a doubling of degrees of freedom, an emergent abelian symmetry associated with entropy, and a topological (BRST) supersymmetry imposing fluctuationdissipation theorem. We illustrate these ideas for a non-linear viscous fluid, and demonstrate that the resulting effective action obeys a generalized fluctuation-dissipation theorem, which guarantees a local form of the second law.
The forearc extension in the Central Kuril Islands and the trench rollback
NASA Astrophysics Data System (ADS)
Baranov, B. V.; Lobkovsky, L. I.; Dozorova, K. A.
2016-07-01
On the basis of bathymetric and seismic data, obtained during cruises 37 (2005) and 41 (2006) of R/V Akademik M.A. Lavrentiev, a new structural scheme of transverse faults in the forearc of the Central Kuril Islands was compiled, the fault kinematics was studied, and a model of the extension zone in the structural pattern of the study area was proposed. According to this model, the trench rollback and development of back-arc basins resulted from the continuous supply of material into the upper mantle convection cell owing to subduction and an increase in the dynamic pressure that pushes the subducting plate, causing it to migrate toward the ocean.
Stratified flows and internal waves in the Central West Atlantic
NASA Astrophysics Data System (ADS)
Grigorenko, K. S.; Makarenko, N. I.; Morozov, E. G.; Tarakanov, R. Yu; Frey, D. I.
2016-06-01
In this paper, we study stratified flows and internal waves in the fracture zones of the Mid Atlantic Ridge. The results of measurements carried out in the 39th and 40th cruises of RV Akademik Sergey Vavilov in the autumn of 2014 and 2015 are presented. Hydrophysical properties of the near-bottom flows are studied experimentally on the basis of CTD- and LADCP profiling. Theoretical analysis involves mathematical formulation of stratified fluid flow which uses CTD-data obtained from field observation in the Vema Fracture Zone region. Spectral properties and kinematic characteristics of internal waves are calculated by finite element method.
NASA Astrophysics Data System (ADS)
Utevsky, Serge Y.; Chernyshev, Alexei V.
2013-02-01
A new species of fish leeches, Dolichobdella rubra gen. n., sp. n., was found in samples collected by RV Akademik M.A. Lavrentyev in the northern Sea of Japan from 470-528 m during the joint Russian-German expedition SoJaBio (Sea of Japan Biodiversity Studies) in August 2010. The leech does not exceed 13 mm in length and has the following morphological characteristics: body elongated, smooth, lacking gills and pulsatile vesicles; eyes and ocelli absent; coloration reddish; female gonopore larger than male one; 6pairs of testisacs; accessory glands, conductive tissue and copulatory area present; ovisacs short; bursa long; coelomic system reduced.
NASA Astrophysics Data System (ADS)
Dmitrevskiy, N. N.; Ananyev, R. A.; Libina, N. V.; Roslyakov, A. G.
2013-05-01
The paper describes a high-resolution seismoacoustic complex for studying the upper sedimentary stratum and seafloor relief. The described complex was used during the 57th cruise of the R/V Akademik M.A. Lavrent'ev in the East Siberian and Laptev seas in the autumn of 2011. The combination of an SES-2000 narrow-beam parametric subbottom profiler and a Gidra 250/500 sidescan sonar has enabled obtaining a series of unique data on the structure of the sedimentary layers and the seafloor relief.
NASA Astrophysics Data System (ADS)
Petrova, V. V.; Skolotnev, S. G.; Chistyakova, N. I.
2010-03-01
In volcanic tuffs, dredged during Cruise 23 of the R/V Akademik Nikolaj Strakhov, accessory zircon was found; except for the mineral-forming components, there were ˜2% of ThO2 and 0.75% of Ce2O3 in zircon. During rapid uplift of magmatic masses to the ocean bottom surface, admixture elements isolated into specific minerals. As a result, destruction structures were formed in the rim parts of primary zircon crystals, and the new-formed association of zircon + thorite + cerite + thoriante + baddeleyite appeared.
Russian deep-sea investigations of Antarctic fauna
NASA Astrophysics Data System (ADS)
Malyutina, Marina
2004-07-01
A review of the Russian deep-sea investigation of Antarctic fauna beginning from the first scientific collection of Soviet whaling fleet expeditions 1946-1952 is presented. The paper deals with the following expeditions, their main tasks and results. These expeditions include three cruises of research vessel (R.V.) Ob in the Indian sector of the Antarctic and in the Southern Pacific (1955-1958); 11 cruises of the R.V. Akademik Kurchatov in the southern Atlantic (November-December 1971); 16 cruises of the R.V. Dmitriy Mendeleev in the Australia-New Zealand area and adjacent water of the Antarctic (December 1975-March 1976); 43 cruises of the R.V. Akademik Kurchatov in the southern Atlantic (October 1985-February 1986); and 43 cruises of the R.V. Dmitriy Mendeleev in the Atlantic sector of the South Ocean (January-May 1989). A list of the main publications on the benthic taxa collected during these expeditions with data of their distribution is presented. The results of Russian explorations of the Antarctic fauna are presented as theoretical conclusions in the following topics: (1) Vertical zonation in the distribution of the Antarctic deep-sea fauna; (2) Biogeographic division of the abyssal and hadal zones; (3) Origin of the Antarctic deep-sea fauna; (4) Distributional pathways of the Antarctic abyssal fauna through the World Ocean.
Nonequilibrium self-energy functional theory
NASA Astrophysics Data System (ADS)
Hofmann, Felix; Eckstein, Martin; Arrigoni, Enrico; Potthoff, Michael
2013-10-01
The self-energy functional theory (SFT) is generalized to describe the real-time dynamics of correlated lattice-fermion models far from thermal equilibrium. This is achieved by starting from a reformulation of the original equilibrium theory in terms of double-time Green's functions on the Keldysh-Matsubara contour. With the help of a generalized Luttinger-Ward functional, we construct a functional Ω̂[Σ] which is stationary at the physical (nonequilibrium) self-energy Σ and which yields the grand potential of the initial thermal state Ω at the physical point. Nonperturbative approximations can be defined by specifying a reference system that serves to generate trial self-energies. These self-energies are varied by varying the reference system's one-particle parameters on the Keldysh-Matsubara contour. In the case of thermal equilibrium, this approach reduces to the conventional SFT. Contrary to the equilibrium theory, however, “unphysical” variations, i.e., variations that are different on the upper and the lower branches of the Keldysh contour, must be considered to fix the time dependence of the optimal physical parameters via the variational principle. Functional derivatives in the nonequilibrium SFT Euler equation are carried out analytically to derive conditional equations for the variational parameters that are accessible to a numerical evaluation via a time-propagation scheme. Approximations constructed by means of the nonequilibrium SFT are shown to be inherently causal, internally consistent, and to respect macroscopic conservation laws resulting from gauge symmetries of the Hamiltonian. This comprises the nonequilibrium dynamical mean-field theory but also dynamical-impurity and variational-cluster approximations that are specified by reference systems with a finite number of degrees of freedom. In this way, nonperturbative and consistent approximations can be set up, the numerical evaluation of which is accessible to an exact
Topological aspects of nonlinear excitonic processes in noncentrosymmetric crystals
NASA Astrophysics Data System (ADS)
Morimoto, Takahiro; Nagaosa, Naoto
2016-07-01
We study excitonic processes second order in the electric fields in noncentrosymmetric crystals. We derive formulas for shift current and second harmonic generation produced by exciton creation, by using the Floquet formalism combined with the Keldysh Green's function method. It is shown that (i) the steady dc shift current flows by exciton creation without dissociation into free carriers and (ii) second harmonic generation is enhanced at the exciton resonance. The obtained formulas clarify topological aspects of these second order excitonic processes which are described by Berry connections of the relevant valence and conduction bands.
NASA Astrophysics Data System (ADS)
Raju, Ch. Narasimha; Chatterjee, Ashok
2016-01-01
The Anderson-Holstein model with Caldeira-Leggett coupling with environment is considered to describe the damping effect in a single molecular transistor (SMT) which comprises a molecular quantum dot (with electron-phonon interaction) mounted on a substrate (environment) and coupled to metallic electrodes. The electron-phonon interaction is first eliminated using the Lang-Firsov transformation and the spectral density function, charge current and differential conductance are then calculated using the non-equilibrium Keldysh Green function technique. The effects of damping rate, and electron-electron and electron-phonon interactions on the transport properties of SMT are studied at zero temperature.
Raju, Ch Narasimha; Chatterjee, Ashok
2016-01-01
The Anderson-Holstein model with Caldeira-Leggett coupling with environment is considered to describe the damping effect in a single molecular transistor (SMT) which comprises a molecular quantum dot (with electron-phonon interaction) mounted on a substrate (environment) and coupled to metallic electrodes. The electron-phonon interaction is first eliminated using the Lang-Firsov transformation and the spectral density function, charge current and differential conductance are then calculated using the non-equilibrium Keldysh Green function technique. The effects of damping rate, and electron-electron and electron-phonon interactions on the transport properties of SMT are studied at zero temperature. PMID:26732725
Raju, Ch. Narasimha; Chatterjee, Ashok
2016-01-01
The Anderson-Holstein model with Caldeira-Leggett coupling with environment is considered to describe the damping effect in a single molecular transistor (SMT) which comprises a molecular quantum dot (with electron-phonon interaction) mounted on a substrate (environment) and coupled to metallic electrodes. The electron-phonon interaction is first eliminated using the Lang-Firsov transformation and the spectral density function, charge current and differential conductance are then calculated using the non-equilibrium Keldysh Green function technique. The effects of damping rate, and electron-electron and electron-phonon interactions on the transport properties of SMT are studied at zero temperature. PMID:26732725
Loop Corrections to Standard Model fields in inflation
NASA Astrophysics Data System (ADS)
Chen, Xingang; Wang, Yi; Xianyu, Zhong-Zhi
2016-08-01
We calculate 1-loop corrections to the Schwinger-Keldysh propagators of Standard-Model-like fields of spin-0, 1/2, and 1, with all renormalizable interactions during inflation. We pay special attention to the late-time divergences of loop corrections, and show that the divergences can be resummed into finite results in the late-time limit using dynamical renormalization group method. This is our first step toward studying both the Standard Model and new physics in the primordial universe.
Nonlinear spin current and magnetoresistance of molecular tunnel junctions.
Waldron, Derek; Haney, Paul; Larade, Brian; MacDonald, Allan; Guo, Hong
2006-04-28
We report on a theoretical study of spin-polarized quantum transport through a Ni-bezenedithiol(BDT)-Ni molecular magnetic tunnel junction (MTJ). Our study is based on carrying out density functional theory within the Keldysh nonequilibrium Green's function formalism, so that microscopic details of the molecular MTJ are taken into account from first principles. A magnetoresistance ratio of approximately 27% is found for the Ni-BDT-Ni MTJ which declines toward zero as bias voltage is increased. The spin currents are nonlinear functions of bias voltage, even changing sign at certain voltages due to specific features of the coupling between molecular states and magnetic leads. PMID:16712257
Inelastic electron tunneling through degenerate and nondegenerate ground state polymeric junctions
NASA Astrophysics Data System (ADS)
Golsanamlou, Z.; Bagheri Tagani, M.; Rahimpour Soleimani, H.
2015-05-01
The inelastic electron transport properties through two polymeric (trans-polyacetylene and polythiophene) molecular junctions are studied using Keldysh nonequilibrium Green function formalism. The Hamiltonian of the polymers is described via Su-Schrieffer-Heeger model and the metallic electrodes are modeled by the wide-band approximation. Results show that the step-like behavior of the current-voltage characteristics is deformed in presence of strong electron-phonon interaction. Also, the magnitude of current is slightly decreased in the phonon assistant electron transport regime. In addition, it is observed that the I-V curves are independent of temperature.
Optimal ultrafast laser pulse-shaping to direct photo-induced phase transitions
NASA Astrophysics Data System (ADS)
Hwang, Bin; Portman, Jenni; Duxbury, Phillip
Photo-induced phase transitions (PIPT) in quantum and/or complex materials are the epitome of challenging non-equilibrium many-body phenomena, that also have a wide range of potential applications. We present a computational approach to finding optimal ultrafast laser pulse shapes to control the outcome of pump-probe PIPT experiments. The Krotov approach for optimal control is combined with a Keldysh Green's function calculation to describe experimental outcomes such as photoemission, transient single particle density of states and optical responses. Results for a simple model charge density wave system will be presented. main author.
Full quantum theory of the chiral anomaly transport in a Weyl semimetal
NASA Astrophysics Data System (ADS)
Lee, Woo-Ram; Park, Kwon; KIAS Team
In relativistic field theory, the chiral anomaly means a violation of the number conservation of chiral fermions. In condensed matter physics, the chiral anomaly can be manifested in a Weyl semimetal as a negative magnetoresistance in the presence of parallel electric and magnetic fields. In this work, we use the Keldysh-Floquet Green's function formalism to develop a full quantum theory of the chiral anomaly transport, which can be valid in a broad range of both electric and magnetic field strengths. The authors thank KIAS Center for Advanced Computation (CAC) for providing computing resources.
NASA Astrophysics Data System (ADS)
Álvarez, Gonzalo A.; Danieli, Ernesto P.; Levstein, Patricia R.; Pastawski, Horacio M.
2007-06-01
An environment interacting with portions of a system leads to multiexponential interaction rates. Within the Keldysh formalism, we fictitiously homogenize the system-environment interaction yielding a uniform decay rate facilitating the evaluation of the propagators. Through an injection procedure we neutralize the fictitious interactions. This technique justifies a stroboscopic representation of the system-environment interaction which is useful for numerical implementation and converges to the natural continuous process. We apply this procedure to a fermionic two-level system and use the Jordan-Wigner transformation to solve a two-spin swapping gate in the presence of a spin environment.
Majorana fermions in the interacting T-shaped double quantum dot
NASA Astrophysics Data System (ADS)
Napitu, B. D.
2015-11-01
Non-equilibrium transport properties of the interacting T-shaped double quantum dot coupled with the topological superconductor are analyzed within the Keldysh Green's function formalism. The low energy characteristics are found to be influenced by the interplay of quantum interference, electronic correlation, and the Majorana induced interaction such that the system can be driven onto either Kondo, Fano or Majorana dominated regime. It is demonstrated that the presence of the Majorana fermions at the edges of superconducting wire can be realized in the differential conductance and the zero-frequency shot noise when the system's low energy is strongly influenced by the quantum interference effect.
NASA Astrophysics Data System (ADS)
Maksimov, A. I.
2011-06-01
Development of cosmonautics and preparation to the first manned space flights are briefly observed. Details of the development of the first Soviet intercontinental ballistic missile R-7, which served as a basis for creating Sputnik, Vostok, Voskhod, Molniya, and Soyuz launchers, are given. The contributions of the outstanding designers of space engineering, W. von Braun, S.P. Korolev, V.P. Glushko, and academician M.V. Keldysh, to the development of astronautics and first manned space missions are demonstrated. A list of test launches and manned flights of Vostok and Mercury spacecrafts and the basic characteristics of Vostok, Redstone, Atlas-D, Voskhod, and Soyuz launchers are presented.
Nonequilibrium GREEN’S Functions for High-Field Quantum Transport Theory
NASA Astrophysics Data System (ADS)
Bertoncini, Rita
A formulation of the Kadanoff-Baym-Keldysh theory of nonequilibrium quantum statistical mechanics is developed in order to describe nonperturbatively the effects of the electric field on electron-phonon scattering in nondegenerate semiconductors. We derive an analytic, gauge-invariant model for the spectral density of energy states that accounts for both intracollisional field effect and collisional broadening simultaneously. A kinetic equation for the quantum distribution function is derived and solved numerically. The nonlinear drift velocity versus applied field characteristics is also evaluated numerically. Many features of our nonlinear theory bear formal resemblance to linear-response theory.
Time-dependent thermoelectric transport for nanoscale thermal machines
NASA Astrophysics Data System (ADS)
Daré, A.-M.; Lombardo, P.
2016-01-01
We analyze an electronic nanoscale thermal machine driven by time-dependent environment: besides bias and gate voltage variations, we consider also the less prevailing time modulation of the couplings between leads and dot. We provide energy and heat current expressions in such situations, as well as expressions for the power exchanged between the dot+leads system and its outside. Calculations are made in the Keldysh nonequilibrium Green's function framework. We apply these results to design a cyclic refrigerator, circumventing the ambiguity of defining energy flows between subsystems in the case of strong coupling. For fast lead-dot coupling modulation, we observe transient currents which cannot be ascribed to charge tunneling.
On the photon-drag effect of photocurrent of surface states of topological insulators
NASA Astrophysics Data System (ADS)
Lee, Hyun C.
2016-05-01
The photocurrent of surface states of topological insulator due to photon-drag effect is computed, being based on pure Dirac model of surface states. The scattering by disorder is taken into account to provide a relaxation mechanism for the photocurrent. The Keldysh-Schwinger formalism has been employed for the systematic calculation of photocurrent. The helicity dependent photocurrent of sizable magnitude transverse to the in-plane photon momentum is found, which is consistent with experimental data. Other helicity independent photocurrents with various polarization states are also calculated.
NASA Astrophysics Data System (ADS)
Bevan, Kirk H.
2014-10-01
We report on a theoretical interpretation of scanning tunneling potentiometry (STP), formulated within the Keldysh non-equilibrium Green's function description of quantum transport. By treating the probe tip as an electron point source/sink, it is shown that this approach provides an intuitive bridge between existing theoretical interpretations of scanning tunneling microscopy and STP. We illustrate this through ballistic transport simulations of the potential drop across an opaque graphene grain boundary, where atomistic features are predicted that might be imaged through high resolution STP measurements. The relationship between the electrochemical potential profile measured and the electrostatic potential drop across such a nanoscale defect is also explored in this model system.
Gkortsas, Vasileios-Marios; Bhardwaj, Siddharth; Lai, Chien-Jen; Hong, Kyung-Han; Falcao-Filho, Edilson L.; Kaertner, Franz X.
2011-07-15
High-order harmonic generation efficiency is theoretically modeled and compared with experiments using 400 and 800 nm driver pulses. It is shown that, for a short drive wavelength and a Keldysh parameter larger than 1, the Ammosov-Delone-Krainov (ADK) ionization model does not give a good agreement between theory and experiment. Since the ADK ionization model only accounts for tunnel ionization, it underestimates the yield of low-order harmonics from the wings of the driver pulse. In contrast, the Yudin-Ivanov ionization model [Phys. Rev. A 64, 013409 (2001)], which accounts for both tunnel and multiphoton ionization, gives much better agreement with the experimental results.
Contour-ordered Green's functions in stochastic field theory
NASA Astrophysics Data System (ADS)
Honkonen, J.
2013-06-01
We briefly review the functional formulation of the perturbation theory for various Green's functions in quantum field theory. In particular, we discuss the contour-ordered representation of Green's functions at a finite temperature. We show that the perturbation expansion of time-dependent Green's functions at a finite temperature can be constructed using the standard Wick rules in the functional form without introducing complex time and evolution backward in time. We discuss the factorization problem for the corresponding functional integral. We construct the Green's functions of the solution of stochastic differential equations in the Schwinger-Keldysh form with a functional-integral representation with explicitly intertwined physical and auxiliary fields.
Tunneling time, what is its meaning?
NASA Astrophysics Data System (ADS)
McDonald, C. R.; Orlando, G.; Vampa, G.; Brabec, T.
2015-03-01
The tunnel time ionization dynamics for bound systems in laser fields are investigated. Numerical analysis for a step function switch-on of the field allows for the tunnel time to be defined as the time it takes the ground state to develop the under-barrier wavefunction components necessary to achieve the static field ionization rate. A relation between the tunnel time and the Keldysh time is established. The definition of the tunnel time is extended to time varying fields and experimental possibilities for measuring the tunnel time are discussed.
Ultrafast Time-Resolved Photoelectric Emission.
Juffmann, Thomas; Klopfer, Brannon B; Skulason, Gunnar E; Kealhofer, Catherine; Xiao, Fan; Foreman, Seth M; Kasevich, Mark A
2015-12-31
The emission times of laser-triggered electrons from a sharp tungsten tip are directly characterized under ultrafast, near-infrared laser excitation at Keldysh parameters of 6.6<γ<19.1. Emission delays up to 10 fs are observed, which are inferred from the energy gain of photoelectrons emitted into a synchronously driven microwave cavity. Few femtosecond timing resolution is achieved in a configuration capable of measuring timing shifts up to 55 ps. The technique can also be used to measure the microwave phase inside the cavity with a precision below 70 fs upon the energy resolved detection of a single electron. PMID:26764997
NASA Astrophysics Data System (ADS)
Semenov, Andrew G.; Zaikin, Andrei D.
2016-07-01
Quantum phase slips (QPSs) generate voltage fluctuations in superconducting nanowires. Employing the Keldysh technique and making use of the phase-charge duality arguments, we develop a theory of QPS-induced voltage noise in such nanowires. We demonstrate that quantum tunneling of the magnetic flux quanta across the wire yields quantum shot noise which obeys Poisson statistics and is characterized by a power-law dependence of its spectrum SΩ on the external bias. In long wires, SΩ decreases with increasing frequency Ω and vanishes beyond a threshold value of Ω at T →0 . The quantum coherent nature of QPS noise yields nonmonotonous dependence of SΩ on T at small Ω .
Quantum scalar corrections to the gravitational potentials on de Sitter background
NASA Astrophysics Data System (ADS)
Park, Sohyun; Prokopec, Tomislav; Woodard, R. P.
2016-01-01
We employ the graviton self-energy induced by a massless, minimally coupled (MMC) scalar on de Sitter background to compute the quantum corrections to the gravitational potentials of a static point particle with a mass M . The Schwinger-Keldysh formalism is used to derive real and causal effective field equations. When evaluated at the one-loop order, the gravitational potentials exhibit a secular decrease in the observed gravitational coupling G. This can also be interpreted as a (time dependent) anti-screening of the mass M.
Highly efficient spin polarizer based on individual heterometallic cubane single-molecule magnets
NASA Astrophysics Data System (ADS)
Dong, Damin
2015-09-01
The spin-polarized transport across a single-molecule magnet [Mn3Zn(hmp)3O(N3)3(C3H5O2)3].2CHCl3 has been investigated using a density functional theory combined with Keldysh non-equilibrium Green's function formalism. It is shown that this single-molecule magnet has perfect spin filter behaviour. By adsorbing Ni3 cluster onto non-magnetic Au electrode, a large magnetoresistance exceeding 172% is found displaying molecular spin valve feature. Due to the tunneling via discrete quantum-mechanical states, the I-V curve has a stepwise character and negative differential resistance behaviour.
Subgap structure in the conductance of a three-terminal Josephson junction
NASA Astrophysics Data System (ADS)
Pfeffer, A. H.; Duvauchelle, J. E.; Courtois, H.; Mélin, R.; Feinberg, D.; Lefloch, F.
2014-08-01
Three-terminal superconductor (S)-normal metal (N)-superconductor (S) Josephson junctions are investigated. In a geometry where a T-shape normal metal is connected to three superconducting reservoirs, new subgap structures appear in the differential resistance for specific combinations of the superconductor chemical potentials. Those correspond to a correlated motion of Cooper pairs within the device that persist well above the Thouless energy and is consistent with the prediction of quartets formed by two entangled Cooper pairs. A simplified nonequilibrium Keldysh-Green's function calculation is presented that supports this interpretation.
NASA Astrophysics Data System (ADS)
Baru, N. A.; Koloskov, A. V.; Yampolsky, Y. M.; Rakhmatulin, R. A.
2016-03-01
The long-term data of the ionospheric Alfven resonance (IAR) observations recorded at the Ukrainian Antarctic Station "Akademik Vernadsky" from 2002 to 2013 and at Sayan Solar Observatory (Mondy, Russia) from 2010 to 2013 are analyzed. IAR fine spectral structure is studied and a previously unknown effect of splitting of the several lowest resonance modes is discovered. The diurnal and seasonal dependencies of this effect are investigated as well as the dependences of the probability of IAR and splitting detection on Solar and geomagnetic activities in the 11-year cycle. The morphological features of the splitting frequency behavior are analyzed and three main characteristic periods of the splitting are identified, namely: the development, the stationary period and the disappearing. Possible mechanisms of the splitting effect are suggested.
Afanas'eva, E S; Bezrukov, V F; Shepeta, Iu B; Moiseenko, E V
2004-01-01
The estimation of individual variability and group dynamics of micronuclei rate in buccal cells of participants of transatlantic march of the VIIth Ukrainian Antarctic expedition (Sevastopol--UAS "Akademik Vernadsky"--Sevastopol) was carried out. The general average rate of micronuclei was 2.20 per thousand. Individual values of micronuclei frequencies varied in wide limits. The maximum value of CV was 92.4% and the minimal one was 48.4%. Individual averages of micronuclei rates varied from 1.70 to 2.78 per thousand. Dependence of individual and group dynamics of micronuclei rates on environmental factors (temperature, atmospheric pressure and storm activity) was tested. No significant correlation of these parameters was found. PMID:15715163
Chipman, D.W.; Rubin, S.I.; Takahashi, T.
1992-08-01
During the fist year of this two-year grant, we have completed the data acquisition phase at sea along the WOCE-S4 section located along 67{degree}S between 73{degree}W and 172{degree}E in the Pacific sector of the Southern Ocean. The expedition was carried out aboard the Russian Research Ship ``Akademik IOFFE`` in the period February 14 through April 6, 1992. The total CO{sub 2} concentration and pCO{sub 2} in a total of about 1290 water samples were determined using a coulometer for total CO{sub 2} and an equilibrator/gas chromatograph system for pCO{sub 2}. Surface water samples were analyzed at all the 112 hydrographic stations occupied. Complete or partial profiles were obtained at 58 stations. In addition, a total of 172 determinations were made at sea for 62 bottles of the Standard Reference Solution.
Measurements of carbon dioxide in the Southern Ocean along the WOCE S-4 section
Chipman, D.W.; Rubin, S.I.; Takahashi, T.
1992-08-01
During the fist year of this two-year grant, we have completed the data acquisition phase at sea along the WOCE-S4 section located along 67{degree}S between 73{degree}W and 172{degree}E in the Pacific sector of the Southern Ocean. The expedition was carried out aboard the Russian Research Ship Akademik IOFFE'' in the period February 14 through April 6, 1992. The total CO{sub 2} concentration and pCO{sub 2} in a total of about 1290 water samples were determined using a coulometer for total CO{sub 2} and an equilibrator/gas chromatograph system for pCO{sub 2}. Surface water samples were analyzed at all the 112 hydrographic stations occupied. Complete or partial profiles were obtained at 58 stations. In addition, a total of 172 determinations were made at sea for 62 bottles of the Standard Reference Solution.
Postmiocene geodynamic evolution of the drake passage, Western Antarctic Region, southern ocean
NASA Astrophysics Data System (ADS)
Teterin, D. E.
2011-08-01
In 1994-2006, the German research vessel, Polarstern, and the Russian research vessel, Akademik Boris Petrov, carried out marine geologic and geophysical explorations in the Western Antarctic Region within the Bellingshausen, Amundsen, and Scotia marginal Seas and the Drake Passage. In these expeditions, new unique data on submarine topography have been collected by a multibeam echosounder, gravity and magnetic measurements have been carried out, multichannel seismic profiling has been performed, and the collections of rock samples have been acquired. The analysis and interpretation of new evidence together with previous geologic and geophysical data for the Drake Passage region have shown that end of spreading in the Aluk Ridge three million years ago resulted in the redistribution of stresses associated with the relative motion of the Antarctic, Scotia, and Phoenix Plates, which, in turn, caused significant tectonic reconstruction of the entire transition zone of the Drake Passage.
The first high-precision gravity survey in the North Pole region
NASA Astrophysics Data System (ADS)
Sokolov, A. V.; Krasnov, A. A.; Koneshov, V. N.; Glazko, V. V.
2016-03-01
The experience with conducting a marine gravity survey onboard a surface vessel under complicated ice conditions at high latitude is described. In 2014, a high-precision marine gravity survey with two modifications of the Chekan-AM gravimeter was carried out in the North Pole region. The measurements were conducted during two months from aboard the Akademik Fedorov research vessel on a given grid with a total length of 10000 km of the routes. As a result, 70000 gravity points at Arctic latitudes including the region of the geographical North Pole itself are acquired. In this paper, we discuss the methodical aspects of conducting the survey and present the accuracy estimates of the gravity measurements. The comparison of the obtained results with the Earth's gravity models demonstrates the absence of systematic errors and the higher spatial resolution of the measurements with the Chekan-AM gravimeters.
Contourite systems in the region of the southern São Paulo Plateau escarpment, South Atlantic
NASA Astrophysics Data System (ADS)
Borisov, D. G.; Murdmaa, I. O.; Ivanova, E. V.; Levchenko, O. V.; Yutsis, V. V.; Frantseva, T. N.
2013-07-01
Seismoacoustic investigations with a high-resolution parametric echo-sounder "SES 2000 deep" carried out on cruises 33, 35, and 37 of the R/V Akademik Ioffe revealed several erosional-depositional contourite systems on the São Paulo Plateau escarpment and its toe in the South Atlantic. Two contourite terraces related to interfaces between different water masses are observable on the escarpment. These terraces presumably reflect the activity of internal waves and turbulent eddies. The São Paulo contourite channel and genetically related drift are traceable along the escarpment toe. Changes in planktonic foraminiferal assemblages in Core AI-2563 retrieved from the summit of the São Paulo contourite drift suggest a shallowing of the Weddell Sea Deep Water mass during glacial times. It is established that the contour current of the Weddell Sea Deep Water and Lower Circumpolar Water considerably affect the formation of contourite depositional systems on the escarpment and its toe.
Erosion-accumulative activity of the bottom currents on the continental rise of Brazil
NASA Astrophysics Data System (ADS)
Borisov, D. G.; Murdmaa, I. O.; Ivanova, E. V.; Roslyakov, A. G.; Anan'ev, R. A.
2013-09-01
Several high-resolution "SES 2000 deep" seismic profiles and a core of bottom sediments were obtained in cruises 33, 35, and 37 of the R/V Akademik Ioffe in the area of the Columbia channel (continental rise of Brazil, South America). The analysis of seismic facies and direct correlation of acoustic and lithological data indicates that sedimentation in this area is mostly controlled by the contour current of the Antarctic Bottom Water (AABW). The gravity flows from seamounts and continental slope only episodically contributed coarser material to the deposition of the muddy contourites. The mixed gravitite-contourite systems consisting of accumulative bodies (drifts) and erosion channels are the results of interaction of these sedimentation processes.
NASA Astrophysics Data System (ADS)
Agarwalla, Bijay Kumar; Kulkarni, Manas; Mukamel, Shaul; Segal, Dvira
2016-07-01
We investigate gain in microwave photonic cavities coupled to voltage-biased double quantum dot systems with an arbitrarily strong dot-lead coupling and with a Holstein-like light-matter interaction, by employing the diagrammatic Keldysh nonequilibrium Green's function approach. We compute out-of-equilibrium properties of the cavity: its transmission, phase response, mean photon number, power spectrum, and spectral function. We show that by the careful engineering of these hybrid light-matter systems, one can achieve a significant amplification of the optical signal with the voltage-biased electronic system serving as a gain medium. We also study the steady-state current across the device, identifying elastic and inelastic tunneling processes which involve the cavity mode. Our results show how recent advances in quantum electronics can be exploited to build hybrid light-matter systems that behave as microwave amplifiers and photon source devices. The diagrammatic Keldysh approach is primarily discussed for a cavity-coupled double quantum dot architecture, but it is generalizable to other hybrid light-matter systems.
Heterostructure quantum confined Stark effect electrooptic modulators operating at 938 nm
NASA Astrophysics Data System (ADS)
Hayduk, Michael J.; Krol, Mark F.; Boncek, Raymond K.
1993-12-01
Electro-optics modulators are a necessary component of emerging optical fiber based local area interconnects. One type of modulator, suitable for use in optical interconnects, is an asymmetric Fabry-Perot reflection modulator (ARM). This type of an intensity modulator uses an electro-optic material as the spacer material to balance the normally unequal front and back mirror reflectances. The quantum confined Franz-Keldysh and Stark effects shift the absorption edge of semiconductor multiple quantum well (MQW) materials to longer wavelengths in the presence of an external electric field applied perpendicular to the MQW layers, thereby changing the reflectance of the etalon. The combined coherence effects of the etalon coupled with the quantum effects of the MQW materials result in a large modulation depth and a low insertion loss. P-I-N diode structures using an In Ha As/GaAs MQW structure as the intrinsic region were fabricated for the purpose of characterizing the electro-absorption associated with different applied electric fields. Quantum confined Franz-Keldysh and Stark shifts were observed for applied electric fields as large as 6.58 x 10000 V/cm. The resulting change in the absorption coefficient was found to be -3.7 x 1000 cm to the minus 1st power which is sufficient to design a high-speed ARM with a large modulation depth and a low insertion loss.
Under-the-barrier dynamics in laser-induced relativistic tunneling.
Klaiber, Michael; Yakaboylu, Enderalp; Bauke, Heiko; Hatsagortsyan, Karen Z; Keitel, Christoph H
2013-04-12
The tunneling dynamics in relativistic strong-field ionization is investigated with the aim to develop an intuitive picture for the relativistic tunneling regime. We demonstrate that the tunneling picture applies also in the relativistic regime by introducing position dependent energy levels. The quantum dynamics in the classically forbidden region features two time scales, the typical time that characterizes the probability density's decay of the ionizing electron under the barrier (Keldysh time) and the time interval which the electron spends inside the barrier (Eisenbud-Wigner-Smith tunneling time). In the relativistic regime, an electron momentum shift as well as a spatial shift along the laser propagation direction arise during the under-the-barrier motion which are caused by the laser magnetic field induced Lorentz force. The momentum shift is proportional to the Keldysh time, while the wave-packet's spatial drift is proportional to the Eisenbud-Wigner-Smith time. The signature of the momentum shift is shown to be present in the ionization spectrum at the detector and, therefore, observable experimentally. In contrast, the signature of the Eisenbud-Wigner-Smith time delay disappears at far distances for pure quasistatic tunneling dynamics. PMID:25167261
Internal wave structures in abyssal cataract flows
NASA Astrophysics Data System (ADS)
Makarenko, Nikolay; Liapidevskii, Valery; Morozov, Eugene; Tarakanov, Roman
2014-05-01
We discuss some theoretical approaches, experimental results and field data concerning wave phenomena in ocean near-bottom stratified flows. Such strong flows of cold water form everywhere in the Atlantic abyssal channels, and these currents play significant role in the global water exchange. Most interesting wave structures arise in a powerful cataract flows near orographic obstacles which disturb gravity currents by forced lee waves, attached hydraulic jumps, mixing layers etc. All these effects were observed by the authors in the Romanche and Chain fracture zones of Atlantic Ocean during recent cruises of the R/V Akademik Ioffe and R/V Akademik Sergei Vavilov (Morozov et al., Dokl. Earth Sci., 2012, 446(2)). In a general way, deep-water cataract flows down the slope are similar to the stratified flows examined in laboratory experiments. Strong mixing in the sill region leads to the splitting of the gravity current into the layers having the fluids with different densities. Another peculiarity is the presence of critical layers in shear flows sustained over the sill. In the case under consideration, this critical level separates the flow of near-bottom cold water from opposite overflow. In accordance with known theoretical models and laboratory measurements, the critical layer can absorb and reflect internal waves generated by the topography, so the upward propagation of these perturbations is blocked from above. High velocity gradients were registered downstream in the vicinity of cataract and it indicates the existence of developed wave structures beyond the sill formed by intense internal waves. This work was supported by RFBR (grants No 12-01-00671-a, 12-08-10001-k and 13-08-10001-k).
Competition between spin-orbit interaction and exchange coupling within a honeycomb lattice ribbon
NASA Astrophysics Data System (ADS)
Su, Yu-Hsin; Chen, Son-Hsien; Hu, C. D.; Chang, Ching-Ray
2016-01-01
Spin density patterns of a pinned magnetic impurity that is embedded in a honeycomb lattice with zigzag edges are investigated by employing a mean-field assisted Landauer-Keldysh formalism. Both the intrinsic spin-orbit coupling and the extrinsic localized magnetic moments are considered, and the effects of the pinning directions and the species of the sublattice on the electron spins are analyzed. A local time-reversal symmetry breaking cannot destroy the equilibrium edge-state spin accumulation that is induced by intrinsic spin-orbit coupling when the pinning field lies in the plane of the ribbon and the embedding position is the A-site at the edge. The induced local spin can be either parallel or antiparallel to the localized impurity moment, depending on the location of the pinned impurity, because itinerant electrons are found only at the B-site of the edge, but not at the A-site.
Broken SU(4) symmetry in a Kondo-correlated carbon nanotube
NASA Astrophysics Data System (ADS)
Schmid, Daniel R.; Smirnov, Sergey; Margańska, Magdalena; Dirnaichner, Alois; Stiller, Peter L.; Grifoni, Milena; Hüttel, Andreas K.; Strunk, Christoph
2015-04-01
Understanding the interplay between many-body phenomena and nonequilibrium in systems with entangled spin and orbital degrees of freedom is a central objective in nanoelectronics. We demonstrate that the combination of Coulomb interaction, spin-orbit coupling, and valley mixing results in a particular selection of the inelastic virtual processes contributing to the Kondo resonance in carbon nanotubes at low temperatures. This effect is dictated by conjugation properties of the underlying carbon nanotube spectrum at zero and finite magnetic field. Our measurements on a clean carbon nanotube are complemented by calculations based on a field-theoretical Keldysh approach to the nonequilibrium Kondo problem which well reproduces the rich experimental observations in Kondo transport.
Out of equilibrium spatio-temporal correlations in the Bose-Hubbard model
NASA Astrophysics Data System (ADS)
Kennett, Malcolm; Fitzpatrick, Matthew
2016-05-01
The Bose-Hubbard model (BHM) provides a model system to study quench dynamics across a quantum phase transition. Theoretically, it has proven challenging to study spatio-temporal correlations in the BHM in dimensions higher than one. We use the Schwinger-Keldysh technique and a strong-coupling expansion to develop a two-particle irreducible formalism to allow us to study spatio-temporal correlations in both the superfluid (SF) and Mott-insulating (MI) regimes during a quantum quench for dimensions higher than one. We obtain equations of motion for both the superfluid order parameter and two-point correlation functions and present numerical results for the evolution of two-time correlation functions. We relate our results to experiments on cold atoms in optical lattices. Supported by NSERC.
A microscopic model of current-induced switching of magnetization.
Sandschneider, N; Nolting, W
2010-01-20
The behaviour of the magnetization in a ferromagnetic metal/nonmagnetic insulator/ferromagnetic metal/paramagnetic metal tunnel junction is studied, using the nonequilibrium Keldysh formalism. The two ferromagnets are described using the single-band Hubbard model. The left one is treated in the mean field approximation and the right ferromagnet within a (nonequilibrium) spectral density approach which takes interactions beyond the mean field into account. When a voltage is applied to the junction we observe a change of the relative orientation of the two magnetizations, which can be switched from parallel to antiparallel alignment and vice versa. This switching appears in a self-consistent way, so there is no need to use half-classical methods like the Landau-Lifshitz-Gilbert equation one. The dependence of the critical voltage at which the magnetization changes its sign on the model parameters can be studied in a systematic way. PMID:21386267
SLIMP: Strong laser interaction model package for atoms and molecules
NASA Astrophysics Data System (ADS)
Zhang, Bin; Zhao, Zengxiu
2015-07-01
We present the SLIMP package, which provides an efficient way for the calculation of strong-field ionization rate and high-order harmonic spectra based on the single active electron approximation. The initial states are taken as single-particle orbitals directly from output files of the general purpose quantum chemistry programs GAMESS, Firefly and Gaussian. For ionization, the molecular Ammosov-Delone-Krainov theory, and both the length gauge and velocity gauge Keldysh-Faisal-Reiss theories are implemented, while the Lewenstein model is used for harmonic spectra. Furthermore, it is also efficient for the evaluation of orbital coordinates wavefunction, momentum wavefunction, orbital dipole moment and calculation of orbital integrations. This package can be applied to quite large basis sets and complex molecules with many atoms, and is implemented to allow easy extensions for additional capabilities.
Finite time calculations for hard parton production relevant to the quark-gluon plasma
NASA Astrophysics Data System (ADS)
Meiring, Ben; Horowitz, W. A.
2015-10-01
AdS/CFT computations have been used to describe the energy loss of QCD-like particles moving through a strongly coupled plasma, but little is understood regarding the initial conditions of these jets. We use the Schwinger-Keldysh finite-time formalism applied to an interacting scalar field theory to derive perturbative expressions detailing the system which exists during the initial stages of a high energy collision. In this paper we calculate <ϕ>(x) for a scalar Yukawa model, demonstrate the finiteness of the energy momentum tensor for λϕ4 to leading order, and derive an expression for the conditional expectation value of operators to aid in the description jet-like behaviour in interacting theories.
Posazhennikova, Anna; Trujillo-Martinez, Mauricio; Kroha, Johann
2016-06-01
A Bose gas in a double-well potential, exhibiting a true Bose-Einstein condensate (BEC) amplitude and initially performing Josephson oscillations, is a prototype of an isolated, nonequilibrium many-body system. We investigate the quasiparticle (QP) creation and thermalization dynamics of this system by solving the time-dependent Keldysh-Bogoliubov equations. We find avalanchelike QP creation due to a parametric resonance between BEC and QP oscillations, followed by slow, exponential relaxation to a thermal state at an elevated temperature, controlled by the initial excitation energy of the oscillating BEC above its ground state. The crossover between the two regimes occurs because of an effective decoupling of the QP and BEC oscillations. This dynamics is analogous to elementary particle creation in models of the early universe. The thermalization in our setup occurs because the BEC acts as a grand canonical reservoir for the quasiparticle system. PMID:27314725
Zou, Fei; Zhu, Lin; Yao, Kailun
2015-01-01
On the basis of the density functional theory combined with the Keldysh nonequilibrium Green’s function method, we investigate the spin-dependent transport properties of single-edge phosphorus-doped ZGNR systems with different widths. The results show a perfect spin filtering effect reaching 100% at a wide bias range in both parallel (P) and antiparallel (AP) spin configurations for all systems, especially for 6-ZGNR-P system. Instructively, for the AP spin configuration, the spin down current of the 4-ZGNR-P system exhibits a negative differential effect. By analyzing the transmission spectrum and the spin-resolved band structures of the electrodes, we elucidate the mechanism for these peculiar properties. Our findings provide a new way to produce multifunctional spintronic devices based on phosphorus-doped zigzag graphene nanoribbons. PMID:26514646
NASA Astrophysics Data System (ADS)
Wetch, Joseph R.; See-pok Wong, Britt, Edward J.; McCracken, Kevin J.; Lin, Raymond; Petrosov, Valeri; Koroteev, Anatoli
1995-01-01
An improved design of the Hall type stationary plasma thruster has been tested in 1994. The test results are presented. The test measures performance, EMI and beam divergence of two models of thrusters from the Russian Keldysh Scientific-Research Institute of Thermal Processes. The first of these engines, T-100 produces 80 mN thruster with power of 1.35 kWe. The other thruster, T-160 is larger and produces 280 nM thrust with 4.5 kWe. Endurance testing of the T-100 for 2000 hours was completed at NIITP. Post operation wear measurements indicate that the insulator life expectency will exceed the 8000 hour design life objective. Improved efficiencies of 48 to 52% were measured for the T-100 and 58-62% (with elevated tank pressure) for the T-160 at specific impulse Isp of 1600 seconds and 2000 seconds respectively.
Ab initio analysis of electron-phonon coupling in molecular devices.
Sergueev, N; Roubtsov, D; Guo, Hong
2005-09-30
We report a first principles analysis of electron-phonon coupling in molecular devices under external bias voltage and during current flow. Our theory and computational framework are based on carrying out density functional theory within the Keldysh nonequilibrium Green's function formalism. Using a molecular tunnel junction of a 1,4-benzenedithiolate molecule contacted by two aluminum leads as an example, we analyze which molecular vibrational modes are most relevant to charge transport under nonequilibrium conditions. We find that the low-lying modes are most important. As a function of bias voltage, the electron-phonon coupling strength can change drastically while the vibrational spectrum changes at a few percent level. PMID:16241682
Thermoelectric effect in an Aharonov-Bohm ring with an embedded quantum dot.
Zheng, Jun; Chi, Feng; Lu, Xiao-Dong; Zhang, Kai-Cheng
2012-01-01
Thermoelectric effect is studied in an Aharonov-Bohm interferometer with an embedded quantum dot (QD) in the Coulomb blockade regime. The electrical conductance, electron thermal conductance, thermopower, and thermoelectric figure-of-merit are calculated by using the Keldysh Green's function method. It is found that the figure-of-merit ZT of the QD ring may be quite high due to the Fano effect originated from the quantum interference effect. Moreover, the thermoelectric efficiency is sensitive to the magnitude of the dot-lead and inter-lead coupling strengthes. The effect of intradot Coulomb repulsion on ZT is significant in the weak-coupling regime, and then large ZT values can be obtained at rather high temperature. PMID:22369454
Pulkovo cooperation of optical observers
NASA Astrophysics Data System (ADS)
Molotov, I.; Abalakin, V. K.; Titenko, V.; , Pozanenko A.; Dorokhova, T. N.; Guseva, I.; Ibragimov, M.; Sukhov, P. P.; Rozales, R.; Mukhamednazarov, S.; Gulyamov, M.; Lupishko, D.; Kiladze, R.; Sochilina, A.; Marshalkina, A.; Khutorovskiy, Z.; Arkharov, A. A.; Korniyenko, G.; Yerofeyeva, A.
2005-01-01
Under the new organization is the cooperation of optical observatory space debris, asteroids and gamma-ray bursts. Currently, with the cooperation of the Pulkovo optical observers (PulKON) collaborate 14 points in Russia, Ukraine, Uzbekistan, Tajikistan, Turkmenistan, Italy, Spain and Bolivia. Regular observations are in Pulkovo, Ussuriisk, Nauchnom, Mayaki and Chuguev. Test observations commenced or will commence in 2005 in Campo Imperatore, Tarija, Maidanak Abastumani Dushak, Kislovodsk and Hissar. For two grants (Ministry of Education and Science of the Russian Federation and INTAS) in step 8 is planned to purchase modern CCDs for re telescopes operating at target indications PulKON and the Centre for collecting and processing information on Space Debris at IPM of Keldysh RAS.
Theory of Green functions of free Dirac fermions in graphene
NASA Astrophysics Data System (ADS)
Hieu Nguyen, Van; Nguyen, Bich Ha; Dung Dinh, Ngoc
2016-03-01
This work is the beginning of our research on graphene quantum electrodynamics (GQED), based on the application of the methods of traditional quantum field theory to the study of the interacting system of quantized electromagnetic field and Dirac fermions in single-layer graphene. After a brief review of the known results concerning the lattice and electronic structures of single-layer graphene we perform the construction of the quantum fields of free Dirac fermions and the establishment of the corresponding Heisenberg quantum equations of these fields. We then elaborate the theory of Green functions of Dirac fermions in a free Dirac fermion gas at vanishing absolute temperature T = 0, the theory of Matsubara temperature Green functions and the Keldysh theory of non-equilibrium Green functions.
Theory of point contact spectroscopy in correlated materials
Lee, Wei-Cheng; Park, Wan Kyu; Arham, Hamood Z.; Greene, Laura H.; Phillips, Philip
2015-01-01
We developed a microscopic theory for the point-contact conductance between a metallic electrode and a strongly correlated material using the nonequilibrium Schwinger-Kadanoff-Baym-Keldysh formalism. We explicitly show that, in the classical limit, contact size shorter than the scattering length of the system, the microscopic model can be reduced to an effective model with transfer matrix elements that conserve in-plane momentum. We found that the conductance dI/dV is proportional to the effective density of states, that is, the integrated single-particle spectral function A(ω = eV) over the whole Brillouin zone. From this conclusion, we are able to establish the conditions under which a non-Fermi liquid metal exhibits a zero-bias peak in the conductance. This finding is discussed in the context of recent point-contact spectroscopy on the iron pnictides and chalcogenides, which has exhibited a zero-bias conductance peak. PMID:25561532
Hilbert transform evaluation for electron-phonon self-energies
NASA Astrophysics Data System (ADS)
Bevilacqua, Giuseppe; Menichetti, Guido; Pastori Parravicini, Giuseppe
2016-01-01
The electron tunneling current through nanostructures is considered in the presence of the electron-phonon interactions. In the Keldysh nonequilibrium formalism, the lesser, greater, advanced and retarded self-energies components are expressed by means of appropriate Langreth rules. We discuss the key role played by the entailed Hilbert transforms, and provide an analytic way for their evaluation. Particular attention is given to the current-conserving lowest-order-expansion for the treament of the electron-phonon interaction; by means of an appropriate elaboration of the analytic properties and pole structure of the Green's functions and of the Fermi functions, we arrive at a surprising simple, elegant, fully analytic and easy-to-use expression of the Hilbert transforms and involved integrals in the energy domain.
NASA Astrophysics Data System (ADS)
Balzer, Karsten; Bauch, Sebastian; Bonitz, Michael
2010-04-01
In this contribution, we discuss the finite-element discrete variable representation (FE-DVR) of the nonequilibrium Green's function and its implications on the description of strongly inhomogeneous quantum systems. In detail, we show that the complementary features of FEs and the DVR allow for a notably more efficient solution of the two-time Schwinger/Keldysh/Kadanoff-Baym equations compared to a general basis approach. Particularly, the use of the FE-DVR leads to an essential speedup in computing the self-energies. As atomic and molecular examples we consider the He atom and the linear version of H+3 in one spatial dimension. For these closed-shell models we, in Hartree-Fock and second Born approximation, compute the ground-state properties and compare with the exact findings obtained from the solution of the few-particle time-dependent Schrödinger equation.
Electric field control of spin transfer torque in multiferroic tunnel junctions
NASA Astrophysics Data System (ADS)
Useinov, Artur; Kalitsov, Alan; Velev, Julian; Kioussis, Nicholas
2014-03-01
Based on model calculations we predict that the spin transfer torque (STT) in magnetic tunnel junctions with ferroelectric barriers can be strongly influenced by the saturated polarization of the barrier. The STT in such multiferroic tunnel junctions is calculated within the non-equilibrium Keldysh formalism generalized for non-collinear transport and implemented in the framework of a single-band tight-binding (TB) model. We calculate the bias dependence of both the in-plane (T∥) and out-of-plane (T⊥) components of STT as a function of the ferroelectric polarization (P) in the barrier. We find that the components of STT strongly depend on both the magnitude and the direction of the polarization. In particular switching of the polarization direction can dramatically alter the value of the STT and can even lead to a change of sign of T∥ and the voltage-induced part of T⊥. The effect is proportional to the magnitude of the polarization.
Garny, M.; Hohenegger, A.; Kartavtsev, A.; Lindner, M.
2010-04-15
In the baryogenesis via leptogenesis scenario the self-energy contribution to the CP-violating parameter plays a very important role. Here, we calculate it in a simple toy model of leptogenesis using the Schwinger-Keldysh/Kadanoff-Baym formalism as starting point. We show that the formalism is free of the double-counting problem typical for the canonical Boltzmann approach. Within the toy model, medium effects increase the CP-violating parameter. In contrast to results obtained earlier in the framework of thermal field theory, the medium corrections are linear in the particle number densities. In the resonant regime quantum corrections lead to modified expressions for the CP-violating parameter and for the decay width. Most notably, in the maximal resonant regime the Boltzmann picture breaks down and an analysis in the full Kadanoff-Baym formalism is required.
Research on third-order susceptibility tensor of silicon at telecom wavelength
NASA Astrophysics Data System (ADS)
Zhang, Yu-Hong; Liu, Hang; Chen, Zhan-Guo; Jia, Gang; Ren, Ce
2010-10-01
In this paper, the electro-induced birefringence based on Kerr effect and Franz-Keldysh effect in bulk silicon crystal at 1.3μm wavelengths has been measured. By using Kerr effect, the third-order susceptibility tensor of bulk crystalline silicon has been calculated.The two independent tensor of silicon X (3) susceptibility can be obtained by calculation (3) 6.22 (1 2.2%) 10 -20 m2 V2 and Xxyxy(3) = and xxxx(3) 9.13 (1 +/-2.2%) 10-20 m2 V 2 = m2/V2. The research can drive the silicon utility in the photo-electricity field.
Finite temperature quasiparticle self-consistent GW approximation
Vanschilfgaarde, Mark; Leonard, Francois; Desjarlais, Michael Paul; Kotani, Takao; Faleev, Sergey V
2005-10-01
We present a new ab initio method for electronic structure calculations of materials at finite temperature (FT) based on the all-electron quasiparticle self-consistent GW (QPscGW) approximation and Keldysh time-loop Green's function approach. We apply the method to Si, Ge, GaAs, InSb, and diamond and show that the band gaps of these materials universally decrease with temperature in contrast with the local density approximation (LDA) of density functional theory (DFT) where the band gaps universally increase. At temperatures of a few eV the difference between quasiparticle energies obtained in FT-QPscGW and FT-LDA approaches significantly reduces. This result suggests that existing simulations of very high temperature materials based on the FT-LDA are more justified then it might appear from well-known LDA band gap errors at zero-temperature.
Impact ionization in GaAs: A screened exchange density-functional approach
Picozzi, S.; Asahi, R.; Geller, C. B.; Continenza, A.; Freeman, A. J.
2001-08-13
Results are presented of a fully ab initio calculation of impact ionization rates in GaAs within the density functional theory framework, using a screened-exchange formalism and the highly precise all-electron full-potential linearized augmented plane wave method. The calculated impact ionization rates show a marked orientation dependence in k space, indicating the strong restrictions imposed by the conservation of energy and momentum. This anisotropy diminishes as the impacting electron energy increases. A Keldysh type fit performed on the energy-dependent rate shows a rather soft edge and a threshold energy greater than the direct band gap. The consistency with available Monte Carlo and empirical pseudopotential calculations shows the reliability of our approach and paves the way to ab initio calculations of pair production rates in new and more complex materials.
The magnetic and transport properties of edge passivated silicene nanoribbon by Mn atoms
NASA Astrophysics Data System (ADS)
Chen, Changpeng; Zhu, Ziqing; Zha, Dace; Qi, Meilan; Wu, Jinping
2016-02-01
The effect of chemical doping on the ZSiNRs with Mn as passivating element replacing H atoms at one edge are investigated by first-principles calculations. The structures optimized in the typical ferromagnetic and antiferromagnetic coupling show that the system leads to an AFM state and achieve half-metallic properties. Also, our first principle approach based on the Keldysh non-equilibrium Green's function method gives the spin-dependent transport properties of the device. When the system changes from parallel to antiparallel configuration. The spin-up current increases rapidly while the spin-up current is still depressed. Further, it is found that the system is a quite good spin filtering device with nearly 80% spin filtering efficiency at a wide bias voltage region and therefore suitable for applications. The mechanisms for these phenomena are proposed in detail.
Fowler-Nordheim emission modified by laser pulses in the adiabatic regime
NASA Astrophysics Data System (ADS)
Rokhlenko, A.; Lebowitz, J. L.
2016-06-01
We investigate enhanced field emission due to a continuous or pulsed oscillating field added to a constant electric field E at the emitter surface. When the frequency of oscillation, field strength, and property of the emitter material satisfy the Keldysh condition γ<1 /2 , one can use the adiabatic approximation for treating the oscillating field, i.e., consider the tunneling through the instantaneous Fowler-Nordheim barrier created by both fields. Due to the great sensitivity of the emission to the field strength, the average tunneling current can be much larger than the current produced by only the constant field. We carry out the computations for arbitrary strong constant electric fields, beyond the commonly used Fowler-Nordheim approximation which exhibit, in particular, an important property of the wave function inside the potential barrier where it is found to be monotonically decreasing without oscillations.
Time-dependent electron transport in HgTe/CdTe quantum wells
NASA Astrophysics Data System (ADS)
Ding, Kai-He; Zhou, Guanghui
2014-02-01
Based on the Floquet theory and Keldysh's nonequilibrium Green's function methods, we study the electron transport through the HgTe/CdTe quantum wells (QWs) irradiated by a monochromatic laser field. We find that when the laser field is applied, the edge states are split into a series of sidebands. When the Fermi level lies among these sidebands, the quantized plateau of the conductance is destroyed. Instead, the conductance versus the radiation frequency exhibits the successive oscillation peaks corresponding to the resonant tunneling through the sidebands of the edge states. The resonant interaction between the quasiparticles and the radiation field opens the gaps in the crossing region of the sidebands, which can be tuned by the radiation strength and frequency. This leads to the shift of the oscillation peaks in the conductance. We also show that the amplitudes of the oscillation peaks in the conductance are governed by the radiation strength and frequency.
Spin and charge transport induced by a twisted light beam on the surface of a topological insulator
NASA Astrophysics Data System (ADS)
Shintani, Kunitaka; Taguchi, Katsuhisa; Tanaka, Yukio; Kawaguchi, Yuki
2016-05-01
We theoretically study spin and charge transport induced by a twisted light beam irradiated on a disordered surface of a doped three-dimensional topological insulator (TI). We find that various types of spin vortices are imprinted on the surface of the TI depending on the spin and orbital angular momentum of the incident light. The key mechanism for the appearance of the unconventional spin structure is the spin-momentum locking in the surface state of the TI. Besides, the diffusive transport of electrons under an inhomogeneous electric field causes a gradient of the charge density, which then induces nonlocal charge current and spin density as well as the spin current. We discuss the relation between these quantities within the linear response to the applied electric field using the Keldysh-Green's function method.
Spin-polarized current of a transistor in single Mn12 molecular magnets.
Park, Joonho; Yang, Heok; Park, K S; Lee, Eok-Kyun
2007-11-01
Focusing on the framework of how to realize the molecular spintronics in a single molecular magnet, we present theoretical studies on the spin-polarized quantum transport behavior through a single Mn12 molecular magnet. Our theoretical results were obtained by carrying out density functional theoretical calculation within the Keldysh nonequilibrium Green function formalism. The ultimate goal of the molecular spintronics is to develop single molecule transistors which generate spin-polarized currents through the molecular magnet. We obtained the density of states, the transmission coefficients and the characteristic features of the current-voltage (I-V) on the spin-polarized transport properties of Mn12 by the theoretical calculation. These results show the possibility for the realization of molecular spintroinics using single molecular magnets. PMID:18047130
NASA Astrophysics Data System (ADS)
Hofmann, C.; Zimmermann, T.; Zielinski, A.; Landsman, A. S.
2016-04-01
The validity of the adiabatic approximation in strong field ionization under typical experimental conditions has recently become a topic of great interest. Experimental results have been inconclusive, in part, due to the uncertainty in experimental calibration of intensity. Here we turn to the time-dependent Schrödinger equation, where all the laser parameters are known exactly. We find that the centre of the electron momentum distribution (typically used for calibration of elliptically and circularly polarized light) is sensitive to non-adiabatic effects, leading to intensity shifts in experimental data that can significantly affect the interpretation of results. On the other hand, the transverse momentum spread in the plane of polarization is relatively insensitive to such effects, even in the Keldysh parameter regime approaching γ ≈ 3. This suggests the transverse momentum spread in the plane of polarization as a good alternative to the usual calibration method, particularly for experimental investigation of non-adiabatic effects using circularly polarized light.
Inflationary Quasiparticle Creation and Thermalization Dynamics in Coupled Bose-Einstein Condensates
NASA Astrophysics Data System (ADS)
Posazhennikova, Anna; Trujillo-Martinez, Mauricio; Kroha, Johann
2016-06-01
A Bose gas in a double-well potential, exhibiting a true Bose-Einstein condensate (BEC) amplitude and initially performing Josephson oscillations, is a prototype of an isolated, nonequilibrium many-body system. We investigate the quasiparticle (QP) creation and thermalization dynamics of this system by solving the time-dependent Keldysh-Bogoliubov equations. We find avalanchelike QP creation due to a parametric resonance between BEC and QP oscillations, followed by slow, exponential relaxation to a thermal state at an elevated temperature, controlled by the initial excitation energy of the oscillating BEC above its ground state. The crossover between the two regimes occurs because of an effective decoupling of the QP and BEC oscillations. This dynamics is analogous to elementary particle creation in models of the early universe. The thermalization in our setup occurs because the BEC acts as a grand canonical reservoir for the quasiparticle system.
Monte Carlo Study of Real Time Dynamics on the Lattice.
Alexandru, Andrei; Başar, Gökçe; Bedaque, Paulo F; Vartak, Sohan; Warrington, Neill C
2016-08-19
Monte Carlo studies involving real time dynamics are severely restricted by the sign problem that emerges from a highly oscillatory phase of the path integral. In this Letter, we present a new method to compute real time quantities on the lattice using the Schwinger-Keldysh formalism via Monte Carlo simulations. The key idea is to deform the path integration domain to a complex manifold where the phase oscillations are mild and the sign problem is manageable. We use the previously introduced "contraction algorithm" to create a Markov chain on this alternative manifold. We substantiate our approach by analyzing the quantum mechanical anharmonic oscillator. Our results are in agreement with the exact ones obtained by diagonalization of the Hamiltonian. The method we introduce is generic and, in principle, applicable to quantum field theory albeit very slow. We discuss some possible improvements that should speed up the algorithm. PMID:27588844
Electron Transport Through Josephson Junction Containing a Dimeric Structure
NASA Astrophysics Data System (ADS)
Val'kov, V. V.; Aksenov, S. V.
2016-02-01
The dc Josephson effect in a superconductor/dimeric molecule/superconductor junction has been investigated by means of the nonequilibrium Green's function method and the Keldysh diagram technique. The application of the atomic representation has allowed to simplify considerably the computation of the supercurrent and occupation numbers and receive the general expressions which take into account all processes of the Andreev reflection in the loopless approach. It is significant that the expressions for the current and occupation numbers are valid for different multilevel structures in the Josephson junction. The sf-exchange interaction between the electron spin and the spins of the dimer leads to the suppression of the critical current due to a new set of Andreev bound states.
Bryan, W. A.; Stebbings, S. L.; English, E. M. L.; Goodworth, T. R. J.; Newell, W. R.; McKenna, J.; Suresh, M.; Srigengan, B.; Williams, I. D.; Turcu, I. C. E.; Smith, J. M.; Divall, E. J.; Hooker, C. J.; Langley, A. J.
2006-01-15
We report an experimental technique for the comparison of ionization processes in ultrafast laser pulses irrespective of pulse ellipticity. Multiple ionization of xenon by 50 fs 790 nm, linearly and circularly polarized laser pulses is observed over the intensity range 10 TW/cm{sup 2} to 10 PW/cm{sup 2} using effective intensity matching (EIM), which is coupled with intensity selective scanning (ISS) to recover the geometry-independent probability of ionization. Such measurements, made possible by quantifying diffraction effects in the laser focus, are compared directly to theoretical predictions of multiphoton, tunnel and field ionization, and a remarkable agreement demonstrated. EIM-ISS allows the straightforward quantification of the probability of recollision ionization in a linearly polarized laser pulse. Furthermore, the probability of ionization is discussed in terms of the Keldysh adiabaticity parameter {gamma}, and the influence of the precursor ionic states present in recollision ionization is observed.
A new type of low temperature conductivity in InSb doped with Mn
NASA Astrophysics Data System (ADS)
Obukhov, Sergey A.
2012-06-01
We investigated unusual low temperature transport properties of InSb single crystals doped with manganese to concentrations in the range of 1017
Relationship between population dynamics and the self-energy in driven non-equilibrium systems
Kemper, Alexander F.; Freericks, James K.
2016-05-13
We compare the decay rates of excited populations directly calculated within a Keldysh formalism to the equation of motion of the population itself for a Hubbard-Holstein model in two dimensions. While it is true that these two approaches must give the same answer, it is common to make a number of simplifying assumptions, within the differential equation for the populations, that allows one to interpret the decay in terms of hot electrons interacting with a phonon bath. Furthermore, we show how care must be taken to ensure an accurate treatment of the equation of motion for the populations due tomore » the fact that there are identities that require cancellations of terms that naively look like they contribute to the decay rates. In particular, the average time dependence of the Green's functions and self-energies plays a pivotal role in determining these decay rates.« less
Aging dynamics of quantum spin glasses of rotors
NASA Astrophysics Data System (ADS)
Kennett, Malcolm P.; Chamon, Claudio; Ye, Jinwu
2001-12-01
We study the long time dynamics of quantum spin glasses of rotors using the nonequilibrium Schwinger-Keldysh formalism. These models are known to have a quantum phase transition from a paramagnetic to a spin-glass phase, which we approach by looking at the divergence of the spin-relaxation rate at the transition point. In the aging regime, we determine the dynamical equations governing the time evolution of the spin response and correlation functions, and show that all terms in the equations that arise solely from quantum effects are irrelevant at long times under time reparametrization group (RPG) transformations. At long times, quantum effects enter only through the renormalization of the parameters in the dynamical equations for the classical counterpart of the rotor model. Consequently, quantum effects only modify the out-of-equilibrium fluctuation-dissipation relation (OEFDR), i.e. the ratio X between the temperature and the effective temperature, but not the form of the classical OEFDR.
Aspects of nonlocality in quantum field theory, quantum gravity and cosmology
NASA Astrophysics Data System (ADS)
Barvinsky, A. O.
2015-01-01
This paper contains a collection of essays on nonlocal phenomena in quantum field theory, gravity and cosmology. Mechanisms of nonlocal contributions to the quantum effective action are discussed within the covariant perturbation expansion in field strengths and spacetime curvatures. Euclidean version of the Schwinger-Keldysh technique for quantum expectation values is presented as a special rule of obtaining the nonlocal effective equations of motion for the mean quantum field from the Euclidean effective action. This rule is applied to a new model of ghost free nonlocal cosmology which can generate the de Sitter (dS) cosmological evolution at an arbitrary value of Λ — a model of dark energy with the dynamical scale selected by a kind of a scaling symmetry breaking mechanism. This model is shown to interpolate between the superhorizon phase of a scalar mediated gravity and the short distance general relativistic limit in a special metric frame related by a nonlocal conformal transformation to the original metric.
Error threshold for the surface code in a superohmic environment
NASA Astrophysics Data System (ADS)
Lopez-Delgado, Daniel A.; Novais, E.; Mucciolo, Eduardo R.; Caldeira, Amir O.
Using the Keldysh formalism, we study the fidelity of a quantum memory over multiple quantum error correction cycles when the physical qubits interact with a bosonic bath at zero temperature. For encoding, we employ the surface code, which has one of the highest error thresholds in the case of stochastic and uncorrelated errors. The time evolution of the fidelity of the resulting two-dimensional system is cast into a statistical mechanics phase transition problem on a three-dimensional spin lattice, and the error threshold is determined by the critical temperature of the spin model. For superohmic baths, we find that time does not affect the error threshold: its value is the same for one or an arbitrary number of quantum error correction cycles. Financial support Fapesp, and CNPq (Brazil).
NASA Astrophysics Data System (ADS)
Usachenko, Vladimir; Kim, Vyacheslav; Pyak, Pavel
2015-05-01
We report about the results of our theoretical study of the strong-field phenomenon of high-order harmonic generation (HHG) in homonuclear diatomics H2+ andH2 irradiated by a high-intensity laser field of mid-infrared wavelengths corresponding to intermediate values of the so-called Keldysh parameter (γ <= 1). The problem is addressed within the length-gauge (LG) formulation of strong-field approximation (SFA) additionally exploiting the density-functional-theory (DFT) method for numerical composition of initial (laser-free) molecular state using the routines of GAUSSIAN-03 code. The results of our present LG-VGA calculation well reproduce a pronounced interference-related minimum arising in high-frequency region of respective molecular HHG spectra and suggesting clear signatures of the field-induced intramolecular interference corresponding to photoelectron emission to intermediate continuum states from different atomic centers.
Anomalous magnetization of a carbon nanotube as an excitonic insulator
NASA Astrophysics Data System (ADS)
Rontani, Massimo
2014-11-01
We show theoretically that an undoped carbon nanotube might be an excitonic insulator—the long-sought phase of matter proposed by Keldysh, Kohn, and others fifty years ago. We predict that the condensation of triplet excitons, driven by intervalley exchange interaction, spontaneously occurs at equilibrium if the tube radius is sufficiently small. The signatures of exciton condensation are its sizable contributions to both the energy gap and the magnetic moment per electron. The increase of the gap might have already been measured, albeit with a different explanation [V. V. Deshpande, B. Chandra, R. Caldwell, D. S. Novikov, J. Hone, and M. Bockrath, Science 323, 106 (2009), 10.1126/science.1165799]. The enhancement of the quasiparticle magnetic moment is a pair-breaking effect that counteracts the weak paramagnetism of the ground-state condensate of excitons. This property could rationalize the anomalous magnitude of magnetic moments recently observed in different devices close to charge neutrality.
NASA Astrophysics Data System (ADS)
Lee, W. Y.; Chien, J. Y.; Wang, D. P.; Huang, K. F.; Huang, T. C.
2002-04-01
Photoreflectance (PR) of surface-intrinsic-n+ type doped GaAs has been measured for various power densities of pump laser. The spectra exhibited many Franz-Keldysh oscillations, whereby the strength of electric field F in the undoped layer can be determined. The thus obtained Fs are subject to photovoltaic effect and are less than built-in field Fbi. In the previous work we have obtained the relation F≈Fbi-δF/2 when δF≪Fbi by using electroreflectance to simulate PR, where δF is the modulating field of the pump beam. In this work a method was devised to evaluate δF by using photoinduced voltages Vs and, hence, the relation can be verified by PR itself. The δFs obtained by Vs are also consistent with those of using imaginary part of fast Fourier transform of PR spectra.
Non-equilibrium electrodynamics in the large N expansion
Mottola, E.
1994-02-01
An effective action technique for the time evolution of a closed system consisting of a mean field interacting with charged fluctuations is presented, and applied specifically to Quantum Electrodynamics. The effective action of QED is first developed in a systematic expansion in 1/N where N is the number of distinct fermion species. Then by making use of the Schwinger-Keldysh closed time path (CTP) formulation of field theory, causality of the resulting equations of motion is ensured. In QED this technique may be used to study the quantum non-equilibrium effects of pair creation in strong electric fields and the scattering and transport processes of a relativistic e{sup +}e{sup {minus}} plasma. Numerical results for these processes in lowest order are presented. The renormalization procedure, connection to quantum transport theory and extension to QCD and other applications of the method are also discussed.
A caveat on building nonlocal models of cosmology
Tsamis, N.C.; Woodard, R.P. E-mail: woodard@phys.ufl.edu
2014-09-01
Nonlocal models of cosmology might derive from graviton loop corrections to the effective field equations from the epoch of primordial inflation. Although the Schwinger-Keldysh formalism would automatically produce causal and conserved effective field equations, the models so far proposed have been purely phenomenological. Two techniques have been employed to generate causal and conserved field equations: either varying an invariant nonlocal effective action and then enforcing causality by the ad hoc replacement of any advanced Green's function with its retarded counterpart, or else introducing causal nonlocality into a general ansatz for the field equations and then enforcing conservation. We point out here that the two techniques access very different classes of models, and that neither one of them may represent what would actually arise from fundamental theory.
NASA Astrophysics Data System (ADS)
Anders, Frithjof B.; Schmitt, Sebastian
2010-04-01
Scattering states fulfill the correct boundary conditions of a current carrying open quantum system. Discretizing the energy continuum of these states allows for employing Wilson's numerical renormalization group approach without violating the boundary conditions by using a finite size system. We evolve the analytically known steady-state density operator for a non-interacting quantum-system at finite bias to the full interacting problem by the time-dependent numerical renormalization group after switching on the local charging energy. Using a newly developed algorithm for steady-state nonequilibrium Green functions, we can calculate the current I as function of bias voltage V for arbitrary temperature and magnetic field. A comparison with second-order and GW Kadanoff-Baym-Keldysh results shows excellent agreement for weak interaction strength U.
Continuous third harmonic generation in a terahertz driven modulated nanowire
Hamilton, Kathleen E. De, Amrit; Pryadko, Leonid P.; Kovalev, Alexey A.
2015-06-07
We consider the possibility of observing continuous third-harmonic generation using a strongly driven, single-band one-dimensional metal. In the absence of scattering, the quantum efficiency of frequency tripling for such a system can be as high as 93%. Combining the Floquet quasi-energy spectrum with the Keldysh Green's function technique, we derive a semiclassical master equation for a one-dimensional band of strongly and rapidly driven electrons in the presence of weak scattering by phonons. The power absorbed from the driving field is continuously dissipated by phonon modes, leading to a quasi-equilibrium in the electron distribution. We use the Kronig-Penney model with varying effective mass to establish the growth parameters of an InAs/InP nanowire near optimal for third harmonic generation at terahertz frequency range.
NASA Astrophysics Data System (ADS)
Matveev, Oleg; Shvaika, Andrij; Devereaux, Thomas; Freericks, James
The charge-density-wave phase of the Falicov-Kimball model displays a number of anomalous behavior including the appearance of subgap density of states as the temperature increases. These subgap states should have a significant impact on transport properties, particularly the nonlinear response of the system to a large dc electric field. Using the Kadanoff-Baym-Keldysh formalism, we employ nonequilibrium dynamical mean-field theory to exactly solve for this nonlinear response. We examine both the current and the order parameter of the conduction electrons as the ordered system is driven by a dc electric field. Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine, Lviv, Ukraine.
Microscopic theory of sound propagation in the superfluid 3He aerogel system
NASA Astrophysics Data System (ADS)
Higashitani, S.; Miura, M.; Yamamoto, M.; Nagai, K.
2005-04-01
We present a theory of sound propagation in superfluid He3 confined in aerogel, taking dragged aerogel motion into account. The superfluid dynamics coupled with the aerogel motion is formulated by use of the Keldysh Green’s function for weak-coupling superfluid Fermi liquid. We apply the theory to the hydrodynamic regime and calculate the attenuation of a hydrodynamic longitudinal sound mode, the so-called fast mode. The result is compared to the acoustic experiment reported by the Northwestern University group [R. Nomura, G. Gervais, T. M. Haard, Y. Lee, N. Mulders, and W. P. Halperin, Phys. Rev. Lett. 85, 4325 (2000); G. Gervais, R. Nomura, T. M. Haard, Y. Lee, N. Mulders, and W. P. Halperin, J. Low Temp. Phys. 122, 1 (2001)]. We find reasonable agreement between the theory and the experiment.
Large photocurrents in GaN porous structures with a redshift of the photoabsorption edge
NASA Astrophysics Data System (ADS)
Sato, Taketomo; Kumazaki, Yusuke; Kida, Hirofumi; Watanabe, Akio; Yatabe, Zenji; Matsuda, Soichiro
2016-01-01
Photoresponse and photoabsorption properties of GaN porous structures were investigated by measuring photocurrent and spectroscopic photoabsorption under monochromatic light with various wavelengths. The measured photocurrents on the porous GaN electrodes were larger than those on the planar electrodes due to the unique features of the former electrode, such as large surface area and low photoreflectance properties. Moreover, the photocurrents were observed even under illumination with wavelength of 380 nm, corresponding to photon energy of 3.26 eV, which is 130 meV lower than the bandgap energy of bulk GaN. A potential simulation revealed that a high-electric field was induced at the pore tips due to modification of the potential in the porous structures. The observed redshift of the photoabsorption edge can be qualitatively explained by the Franz-Keldysh effect.
NASA Astrophysics Data System (ADS)
Shevlyagin, Alexander; Goroshko, Dmitry; Chusovitin, Evgeniy; Galkin, Konstantin; Galkin, Nikolay
2015-07-01
Using solid phase epitaxy of thin Fe films and molecular beam epitaxy of Si, p-Si/β-FeSi2 nanocrystallites/n-Si(001) diode structure was fabricated. The diode exhibited a current responsivity of 15 mA/W and external quantum efficiency of about 1% at a wavelength of 1300 nm at 120 K without bias and 200 mA/W and 10%, respectively, at -30 V. The device specific detectivity calculated at 120 K in zero bias conditions of 2.1 × 1011 cm·Hz1/2/W at a wavelength of 1.3 µm is the highest ever reported for Si/β-FeSi2 systems. The Franz-Keldysh effect gives grounds for applying such systems not only for the development of optrons but also for that of electro-optical modulators.
Surface potential barrier in m-plane GaN studied by contactless electroreflectance
NASA Astrophysics Data System (ADS)
Janicki, Lukasz; Misiewicz, Jan; Cywiński, Grzegorz; Sawicka, Marta; Skierbiszewski, Czeslaw; Kudrawiec, Robert
2016-02-01
Contactless electroreflectance (CER) is used to study the surface potential barrier in m-plane GaN UN+ [GaN (d = 20,30,50,70 nm)/GaN:Si] structures grown by using molecular beam epitaxy. Clear bandgap-related transitions followed by Franz-Keldysh oscillations (FKO) have been observed in the CER spectra of all samples at room temperature. The built-in electric fields in the undoped cap layers have been determined from the FKO period. From the built-in electric field and the undoped GaN layer thickness, the Fermi level location at the air-exposed m-plane GaN surface has been estimated as 0.42 ± 0.05 eV below the conduction band.
Kudrawiec, R.; Janicki, L.; Gladysiewicz, M.; Misiewicz, J.; Cywinski, G.; Boćkowski, M.; Muzioł, G.
2013-07-29
Two series of N- and Ga-face GaN Van Hoof structures were grown by plasma-assisted molecular beam epitaxy to study the surface potential barrier by contactless electroreflectance (CER). A clear CER resonance followed by strong Franz-Keldysh oscillation of period varying with the thickness of undoped GaN layer was observed for these structures. This period was much shorter for N-polar structures that means smaller surface potential barrier in these structures than in Ga-polar structures. From the analysis of built-in electric field it was determined that the Fermi-level is located 0.27 ± 0.05 and 0.60 ± 0.05 eV below the conduction band for N- and Ga-face GaN surface, respectively.
Wu, Cheng-Han; Wu, Chao-Hsin
2014-10-27
The electrical and optical characteristics of tunnel junction light-emitting transistors (TJLETs) with different indium mole fractions (x = 5% and 2.5%) of the In{sub x}Ga{sub 1−x}As base-collector tunnel junctions have been investigated. Two electron tunneling mechanisms (photon-assisted or direct tunneling) provide additional currents to electrical output and resupply holes back to the base region, resulting in the upward slope of I-V curves and enhanced optical output under forward-active operation. The larger direct tunneling probability and stronger Franz-Keldysh absorption for 5% TJLET lead to higher collector current slope and less optical intensity enhancement when base-collector junction is under reverse-biased.
NASA Astrophysics Data System (ADS)
Takane, Yositake; Hayashi, Masahiko; Ebisawa, Hiromichi
2016-08-01
The time-dependent Ginzburg-Landau equation and the Boltzmann transport equation for charge-density-wave (CDW) conductors are derived from a microscopic one-dimensional model by applying the Keldysh Green's function approach under a quasiclassical approximation. The effects of an external electric field and impurity pinning of the CDW are fully taken into account without relying on a phenomenological argument. These equations simultaneously describe the spatiotemporal dynamics of both the CDW and quasiparticles; thus, they serve as a starting point to develop a general framework to analyze various nonequilibrium phenomena, such as current conversion between the CDW condensate and quasiparticles, in realistic CDW conductors. It is shown that, in typical situations, the equations correctly describe the nonlinear behavior of electric conductivity in a simpler manner.
Heat transport in nonuniform superconductors
NASA Astrophysics Data System (ADS)
Richard, Caroline; Vorontsov, Anton B.
2016-08-01
We calculate electronic energy transport in inhomogeneous superconductors using a fully self-consistent nonequilibrium quasiclassical Keldysh approach. We develop a general theory and apply it to a superconductor with an order parameter that forms domain walls of the type encountered in the Fulde-Ferrell-Larkin-Ovchinnikov state. The heat transport in the presence of a domain wall is inherently anisotropic and nonlocal. The bound states in the nonuniform region play a crucial role and control heat transport in several ways: (i) they modify the spectrum of quasiparticle states and result in Andreev reflection processes and (ii) they hybridize with the impurity band and produce a local transport environment with properties very different from those in a uniform superconductor. As a result of this interplay, heat transport becomes highly sensitive to temperature, magnetic field, and disorder. For strongly scattering impurities, we find that the transport across domain walls at low temperatures is considerably more efficient than in the uniform superconducting state.
Theory of light-enhanced phonon-mediated superconductivity
NASA Astrophysics Data System (ADS)
Sentef, M. A.; Kemper, A. F.; Georges, A.; Kollath, C.
2016-04-01
We investigate the dynamics of a phonon-mediated superconductor driven out of equilibrium. The electronic hopping amplitude is ramped down in time, resulting in an increased electronic density of states. The dynamics of the coupled electron-phonon model is investigated by solving Migdal-Eliashberg equations for the double-time Keldysh Green's functions. The increase of the density of states near the Fermi level leads to an enhancement of superconductivity when the system thermalizes to the new state at the same temperature. We provide a time- and momentum-resolved view on this thermalization process and show that it involves fast processes associated with single-particle scattering and much slower dynamics associated with the superconducting order parameter. The importance of electron-phonon coupling for the rapid enhancement and the efficient thermalization of superconductivity is demonstrated, and the results are compared to a BCS time-dependent mean-field approximation.
Pikhtin, A. N. Komkov, O. S.; Bazarov, K. V.
2006-05-15
The effect of external electric field on interband optical transitions in single In{sub x}Ga{sub 1-x}As/GaAs quantum wells is studied by electroreflectance spectroscopy. A procedure is suggested for separating the contribution of particular exciton transitions to the complicated modulation spectrum. Nontrivial field dependences of the probability of optical transitions forbidden by the symmetry are observed experimentally. The data are compared with the corresponding theoretical dependences. The strength of the internal electric field in the region of the quantum well is determined from Frantz-Keldysh's oscillations. Under certain electric fields, the probability of transitions forbidden with no field is higher than the probability of transitions allowed by the symmetry.
Bias effects on the electronic spectrum of a molecular bridge
Phillips, Heidi; Prociuk, Alexander; Dunietz, Barry D
2011-01-01
In this paper the effect of bias and geometric symmetry breaking on the electronic spectrum of a model molecular system is studied. Geometric symmetry breaking can either enhance the dissipative effect of the bias, where spectral peaks are disabled, or enable new excitations that are absent under zero bias conditions. The spectralanalysis is performed on a simple model system by solving for the electronic response to an instantaneously impulsive perturbation in the dipole approximation. The dynamical response is extracted from the electronic equations of motion as expressed by the Keldysh formalism. This expression provides for the accurate treatment of the electronic structure of a bulk-coupled system at the chosen model Hamiltonian electronic structure level.
Long-lived nonequilibrium states in the Hubbard model with an electric field
NASA Astrophysics Data System (ADS)
Joura, Alexander V.; Freericks, J. K.; Lichtenstein, Alexander I.
2015-06-01
We study the single-band Hubbard model in the presence of a large spatially uniform electric field out of equilibrium. Using the Keldysh nonequilibrium formalism, we solve the problem using perturbation theory in the Coulomb interaction U . We present numerical results for the charge current, the total energy of the system, and the double occupancy on an infinite-dimensional hypercubic lattice with nearest-neighbor hopping. The system is isolated from an external bath and is in the paramagnetic state. We show that an electric field pulse can drive the system to a steady nonequilibrium state, which does not evolve into a thermal state. We compare results obtained within second-order perturbation theory (SOPT), self-consistent SOPT, and iterated perturbation theory (IPT). We also discuss the importance of initial conditions for a system which is not coupled to an external bath.
Long-range magnetic response of the XY spin chain under far-from-equilibrium conditions
NASA Astrophysics Data System (ADS)
Gorczyca–Goraj, Anna; Mierzejewski, Marcin; Prosen, Tomaž
2010-05-01
Within the formalism of the Keldysh Green’s functions we investigate long-range response of an anisotropic XY chain to the local magnetic field. This field couples to a single spin on a selected lattice site. The system is driven out of equilibrium by a coupling to two semi-infinite XX spin chains. We demonstrate that the long-range response becomes enhanced by a few orders of magnitude upon application of nonequilibrium conditions. This enhancement does not occur in the isotropic XX chain. Our results agree with the recently predicted nonequilibrium-driven long-range magnetic correlations [T. Prosen and I. Pižorn, Phys. Rev. Lett. 101, 105701 (2008)]. We argue that this effect may be observed in quasi-one-dimensional triplet superconductors.
NASA Astrophysics Data System (ADS)
Hanai, R.; Littlewood, P. B.; Ohashi, Y.
2016-05-01
We theoretically investigate a Bose-condensed exciton gas out of equilibrium. Within the framework of the combined BCS-Leggett strong-coupling theory with the non-equilibrium Keldysh formalism, we show how the Bose-Einstein condensation (BEC) of excitons is suppressed to eventually disappear, when the system is in the non-equilibrium steady state. The supply of electrons and holes from the bath is shown to induce quasi-particle excitations, leading to the partial occupation of the upper branch of Bogoliubov single-particle excitation spectrum. We also discuss how this quasi-particle induction is related to the suppression of exciton BEC, as well as the stability of the steady state.
NASA Astrophysics Data System (ADS)
Yan, Jiawei; Ke, Youqi
2016-07-01
Electron transport properties of nanoelectronics can be significantly influenced by the inevitable and randomly distributed impurities/defects. For theoretical simulation of disordered nanoscale electronics, one is interested in both the configurationally averaged transport property and its statistical fluctuation that tells device-to-device variability induced by disorder. However, due to the lack of an effective method to do disorder averaging under the nonequilibrium condition, the important effects of disorders on electron transport remain largely unexplored or poorly understood. In this work, we report a general formalism of Green's function based nonequilibrium effective medium theory to calculate the disordered nanoelectronics. In this method, based on a generalized coherent potential approximation for the Keldysh nonequilibrium Green's function, we developed a generalized nonequilibrium vertex correction method to calculate the average of a two-Keldysh-Green's-function correlator. We obtain nine nonequilibrium vertex correction terms, as a complete family, to express the average of any two-Green's-function correlator and find they can be solved by a set of linear equations. As an important result, the averaged nonequilibrium density matrix, averaged current, disorder-induced current fluctuation, and averaged shot noise, which involve different two-Green's-function correlators, can all be derived and computed in an effective and unified way. To test the general applicability of this method, we applied it to compute the transmission coefficient and its fluctuation with a square-lattice tight-binding model and compared with the exact results and other previously proposed approximations. Our results show very good agreement with the exact results for a wide range of disorder concentrations and energies. In addition, to incorporate with density functional theory to realize first-principles quantum transport simulation, we have also derived a general form of
Burning Plastics Investigated in Space for Unique US/Russian Cooperative Project
NASA Technical Reports Server (NTRS)
Friedman, Robert
2000-01-01
It is well known that fires in the low-gravity environment of Earth-orbiting spacecraft are different from fires on Earth. The flames lack the familiar upward plume, which is the result of gravitational buoyancy. These flames, however, are strongly influenced by minor airflow currents. A recent study conducted in low gravity (microgravity) on the Russian orbital station Mir used burning plastic rods mounted in a small chamber with a controllable fan to expose the flame to airflows of different velocities. In this unique project, a Russian scientific agency, the Keldysh Research Center, furnished the apparatus and directed the Mir tests, while the NASA Glenn Research Center at Lewis Field provided the test materials and the project management. Reference testing and calibrations in ground laboratories were conducted jointly by researchers at Keldysh and at the NASA Johnson Space Center's White Sands Test Facility. Multiple samples of three different plastics were burned in the tests: Delrin, a common material for valve bodies; PMMA, a plastic "glass"; and polyethylene, a familiar material for containers and films. Each burned with a unique spherical or egg-shaped flame that spread over the rod. The effect of varying the airflow was dramatic. At the highest airflow attainable in the combustion chamber, nearly 10 cm/sec (a typical ventilation breeze), the flames were bright and strong. As airflow velocity decreased, the flames became shorter but wider. In addition, the flames became less bright, and for PMMA and polyethylene, they showed two colors, a bright part decreasing in volume and a nearly invisible remainder (see the photographs). Finally, at a very low velocity, the flames extinguished. For the plastics tested, this minimum velocity was very low, around 0.3 to 0.5 cm/sec. This finding confirms that at least a slight airflow is required to maintain a flame in microgravity for these types of materials.
NASA Astrophysics Data System (ADS)
Zhao, Qiancheng; Guclu, Caner; Huang, Yuwang; Campione, Salvatore; Capolino, Filippo; Boyraz, Ozdal
2015-02-01
Directive optical leaky wave antennas (OLWAs) with tunable radiation pattern are promising integrated optical modulation and scanning devices. OLWAs fabricated using CMOS-compatible semiconductor planar waveguide technology have the potential of providing high directivity with electrical tunability for modulation and switching capabilities. We experimentally demonstrate directive radiation from a silicon nitride (Si3N4) waveguide-based OLWA. The OLWA design comprises 50 crystalline Si perturbations buried inside the waveguide, with a period of 1 μm, each with a length of 260 nm and a height of 150 nm, leading to a directive radiation pattern at telecom wavelengths. The measured far-field radiation pattern at the wavelength of 1540 nm is very directive, with the maximum intensity at the angle of 84.4° relative to the waveguide axis and a half-power beam width around 6.2°, which is consistent with our theoretical predictions. The use of semiconductor perturbations facilitates electronic radiation control thanks to the refractive index variation induced by a carrier density change in the perturbations. To assess the electrical modulation capability, we study carrier injection and depletion in Si perturbations, and investigate the Franz-Keldysh effect in germanium as an alternative way. We theoretically show that the silicon wire modulator has a -3 dB modulation bandwidth of 75 GHz with refractive index change of 3×10-4 in depletion mode, and 350 MHz bandwidth with refractive index change of 1.5×10-2 in injection mode. The Franz-Keldysh effect has the potential to generate very fast modulation in radiation control at telecom wavelengths.
Full-counting statistics of transient energy current in mesoscopic systems
NASA Astrophysics Data System (ADS)
Yu, Zhizhou; Tang, Gao-Min; Wang, Jian
2016-05-01
We investigate the full-counting statistics (FCS) of energy flow carried by electrons in the transient regime. Based on a two-measurement scheme, we formulate a nonequilibrium Keldysh Green's function theory to compute the generating function for FCS of energy transport. Specifically, we express the generating function using the path integral along the Keldysh contour and obtain an exact solution of the generating function using the Grassmann algebra. With this formalism, we calculate the transient energy current and higher-order cumulants for both single- and double-quantum-dot (QD) systems in the transient regime. To examine the finite bandwidth effect of leads to the FCS of energy transport, we have used an exact solvable model with a Lorentizian linewidth where all nonequilibrium Green's functions can be solved exactly in the time domain. It is found that the transient energy current exhibits damped oscillatory behavior. For the single quantum dot system the frequency of oscillation is independent of bandwidth of the leads while the decay rate of the oscillation amplitude is determined by the lifetime of resonant state which increases as the bandwidth decreases. At short times, a universal scaling of maximum amplitude of normalized cumulants is identified for the single-QD system. For the double-QD system, the damped oscillation of energy current is dominated by Rabi oscillation with frequency approximately proportional to the coupling constant between two quantum dots. In general, the transient energy current increases when the coupling between two QDs is stronger. However, when the interdot coupling is larger than half of the external bias the transient energy current is suppressed significantly. All these results can be understood analytically.
NASA Astrophysics Data System (ADS)
Skolotnev, S. G.; Tsukanov, N. V.; Turko, N. N.; Peyve, A. A.
2003-04-01
The analysis of the bottom relief structure investigated with multibeam SIMRAD 12S and sedimentary cover of depressions investigeted with PARASAUND in the MAR crest zone near Sierra-Leone Fault (22 Cruise of the RV "Akademik Nikolay Strachov", and 10 Cruise of the RV "Akademik Ioffe") point on the complicated character of the tectonic activity distribution in this region. The left-lateral displacements of the rift velley and the absence of transform faults are typical for this region. Two extremely deep rift depressions (up to 5000 m) are located in the rift valley: one on 5°54'N latitude (Markov depression) and the other on 5°46'N latitude. About 40 m sediments cover their bottom. On contary, in the depression located parallel to the rift valley directly to the west from the two mentioned rift depressions the sedimentary cover is absent and bottom has very dissected, apparently volcanic, relief. In the MAR crest zone in 20 miles to the south-west from the Markov and 5°46'N depressions one can see a system of depressions oriented both parallel and oblique to the rift valley. There are filled by the sediments of different thickness. The sedimentary cover of these depressions often is tired and deformed by diapir and horst uplifts. Dredging data show, that basalts, which represent, according to their petro-geo-chemical characteristics the enriched MORB basalts and alkaline basalts compose these uplifts. Irregular distribution and character of composition of the sediments in the depressions of crest zone of the MAR segment under consideration along with high volcanic activity outside the axial spreding zone show that tectonic and volcanic activity in this area are distributed all over the crest zone. The complicated character of this activity is obviosly caused by two reasons. From one hand it may be a deep mantle plum, as inferred from basalt composition and from the other hand it may be the lithosphere blocks displacements along the left-lateral strike slips.
NASA Astrophysics Data System (ADS)
Sakerin, S. M.; Bobrikov, A. A.; Bukin, O. A.; Golobokova, L. P.; Pol'kin, Vas. V.; Pol'kin, Vik. V.; Shmirko, K. A.; Kabanov, D. M.; Khodzher, T. V.; Onischuk, N. A.; Pavlov, A. N.; Potemkin, V. L.; Radionov, V. F.
2015-11-01
We presented the results of expedition measurements of the set of physical-chemical characteristics of atmospheric aerosol in areas of the Arctic and Far East seas, performed onboard RV Akademik Fedorov (17 August-22 September 2013) and RV Professor Khljustin (24 July-7 September 2013). The specific features of spatial distribution and time variations of aerosol optical depth (AOD) of the atmosphere in the wavelength range of 0.34-2.14 μm and boundary layer height, aerosol and black carbon mass concentrations, and disperse and chemical composition of aerosol are discussed. Over the Arctic Ocean (on the route of RV Akademik Fedorov) there is a decrease in aerosol and black carbon concentrations in a northeastern direction: higher values were observed in the region of Spitsbergen and near the Kola Peninsula; and minimum values were observed at northern margins of the Laptev Sea. Average AOD (0.5 μm) values in this remote region were 0.03; the aerosol and black carbon mass concentrations were 875 and 22 ng m-3, respectively. The spatial distributions of most aerosol characteristics over Far East seas show their latitudinal decrease in the northern direction. On transit of RV Professor Khljustin from the Japan Sea to the Chukchi Sea, the aerosol number concentration decreased on average from 23.7 to 2.5 cm-3, the black carbon mass concentration decreased from 150 to 50 ng m-3, and AOD decreased from 0.19 to 0.03. We analyzed the variations in the boundary layer height, measured by ship-based lidar: the average value was 520 m, and the maximal value was 1200 m. In latitudinal distribution of the boundary layer height, there is a characteristic minimum at a latitude of ~ 55° N. For water basins of eight seas, we present the chemical compositions of the water-soluble aerosol fraction (ions, elements) and small gas-phase species, as well as estimates of their vertical fluxes. It is shown that substances are mainly (75-89 %) supplied from the atmosphere to the sea
NASA Astrophysics Data System (ADS)
Sakerin, S. M.; Bobrikov, A. A.; Bukin, O. A.; Golobokova, L. P.; Pol'kin, Vas. V.; Pol'kin, Vik. V.; Shmirko, K. A.; Kabanov, D. M.; Khodzher, T. V.; Pavlov, A. N.; Potemkin, V. L.; Radionov, V. F.
2015-06-01
We presented the results of expedition measurements of the set of physical-chemical characteristics of atmospheric aerosol in water basins of Arctic and Far East seas, performed onboard RV Akademik Fedorov (17 August-22 September 2013) and RV Professor Khljustin (24 July-7 September 2013). The specific features of spatial distribution and time variations of aerosol optical depth (AOD) of the atmosphere in the wavelength range of 0.34-2.14 μm and boundary layer height, aerosol and black carbon mass concentrations, and disperse and chemical composition of aerosol are discussed. Over the Arctic Ocean (on the route of RV Akademik Fedorov) there is a decrease in aerosol and black carbon concentrations in northeastern direction: higher values were observed in the region of Spitsbergen and near the Kola Peninsula; and minimum values were observed at northern margins of the Laptev Sea. Average AOD (0.5 μm) values in this remote region were 0.03; the aerosol and black carbon mass concentrations were 875 and 22 ng m-3, respectively. The spatial distributions of most aerosol characteristics over Far East seas show their latitudinal decrease in the northern direction. On transit of RV Professor Khljustin from Japan to Chukchi Sea, the aerosol number concentration decreased, on the average, from 23.7 to 2.5 cm-3, the black carbon mass concentration decreased from 150 to 50 ng m-3, and AOD decreased from 0.19 to 0.03. We analyzed the variations in the boundary layer height, measured by ship-based lidar: the average value was 520 m, and the maximal value was 1200 m. In latitudinal distribution of the boundary layer height, there is a characteristic minimum at latitude of ∼ 55° N. For water basins of eight seas, we present the chemical compositions of water-soluble aerosol fraction (ions, elements) and small gaseous impurities, as well as estimates of their vertical fluxes. It is shown that substances are mainly (75-89 %) supplied from the atmosphere to the sea surface
Arctic summer school onboard an icebreaker
NASA Astrophysics Data System (ADS)
Alexeev, Vladimir A.; Repina, Irina A.
2014-05-01
The International Arctic Research Center (IARC) of the University of Alaska Fairbanks conducted a summer school for PhD students, post-docs and early career scientists in August-September 2013, jointly with an arctic expedition as a part of NABOS project (Nansen and Amundsen Basin Observational System) onboard the Russian research vessel "Akademik Fedorov". Both the summer school and NABOS expedition were funded by the National Science Foundation. The one-month long summer school brought together graduate students and young scientists with specialists in arctic oceanography and climate to convey to a new generation of scientists the opportunities and challenges of arctic climate observations and modeling. Young scientists gained hands-on experience during the field campaign and learned about key issues in arctic climate from observational, diagnostic, and modeling perspectives. The summer school consisted of background lectures, participation in fieldwork and mini-projects. The mini-projects were performed in collaboration with summer school instructors and members of the expedition. Key topics covered in the lectures included: - arctic climate: key characteristics and processes; - physical processes in the Arctic Ocean; - sea ice and the Arctic Ocean; - trace gases, aerosols, and chemistry: importance for climate changes; - feedbacks in the arctic system (e.g., surface albedo, clouds, water vapor, circulation); - arctic climate variations: past, ongoing, and projected; - global climate models: an overview. An outreach specialist from the Miami Science Museum was writing a blog from the icebreaker with some very impressive statistics (results as of January 1, 2014): Total number of blog posts: 176 Blog posts written/contributed by scientists: 42 Blog views: 22,684 Comments: 1,215 Number of countries who viewed the blog: 89 (on 6 continents) The 33-day long NABOS expedition started on August 22, 2013 from Kirkenes, Norway. The vessel ("Akademik Fedorov") returned to
NASA Astrophysics Data System (ADS)
Hui, F.; Zhai, M.; Li, X.; Cheng, X.; Heil, P.; Zhao, T.
2014-12-01
During the 30th Chinese Antarctic Expedition in 2013/14, the Chinese ice-breaker vessel RV Xuelong answered a rescue call for the Russian vessel Akademik Shokalskiy. While assisting the repatriation of personnel from the Russian vessel to the Australian RV Australis, the RV Xuelong itself became entrapped within the compacted ice in the Adelie Depression region. Here we present our analysis of MODIS and SAR imagery, to provide an in detail description of the regional sea ice conditions, which led to beset the RV Xuelong for ~6 days. The remotely sensed imagery clearly revealed the sea-ice characteristics during the four stages of the entrapment: gathering stage, compaction stage, dispersion stage and calving stage. Here we present our evaluation of the four factors characterizing the local sea-ice conditions during the late Dec 2013 and early January 2014: coastal current, wind, tide and temperature. This study demonstrates that high spatio-temporal resolution remote sensing data are required to monitor the local and regional sea-ice changes with view to avoid future entrapping of vessels due to drastic changes and to work towards improved understanding of sea-atmosphere-ice interactions.
The frontal structure in Drake Passage based on the data of the section in January 2010
NASA Astrophysics Data System (ADS)
Tarakanov, Roman
2014-05-01
The frontal structure in the region of Drake Passage is investigated on the basis of data of Absolute Dynamic Topography (ADT) of French agency CLS (DT-Global-MADT-Upd product, http://aviso.oceanobs.com), and CTD- and SADCP-measurements along the hydrophysical section carried out across the passage from Smith Isl. (just to the east of the Hero F.Z.) to the Cape Horn onboard R/V "Akademik Ioffe" in January 2010. The investigation was similar to the analysis performed on the basis of data of the section carried out two weeks earlier onboard the same vessel south of Africa. Fine-jet structure of the ACC was detected in Drake Passage as well as to the south of Africa where twelve ACC jets were found. Eleven jets of the Antarctic Circumpolar Current (ACC) were revealed in Drake Passage. These were five jets of the Subantarctic Current (the band of Subantarctic Front), four jets of the South Polar Current (the band of Polar Front), and two jets of the South Antarctic Current (the band of Southern ACC Front). Two jets of the South Antarctic Current were joined in a single "super-jet" according to the velocity measurements in the section. The others were manifested by the local velocity maxima in the surface layer.
Cyclone-induced rapid creation of extreme Antarctic sea ice conditions
Wang, Zhaomin; Turner, John; Sun, Bo; Li, Bingrui; Liu, Chengyan
2014-01-01
Two polar vessels, Akademik Shokalskiy and Xuelong, were trapped by thick sea ice in the Antarctic coastal region just to the west of 144°E and between 66.5°S and 67°S in late December 2013. This event demonstrated the rapid establishment of extreme Antarctic sea ice conditions on synoptic time scales. The event was associated with cyclones that developed at lower latitudes. Near the event site, cyclone-enhanced strong southeasterly katabatic winds drove large westward drifts of ice floes. In addition, the cyclones also gave southward ice drift. The arrival and grounding of Iceberg B9B in Commonwealth Bay in March 2011 led to the growth of fast ice around it, forming a northward protruding barrier. This barrier blocked the westward ice drift and hence aided sea ice consolidation on its eastern side. Similar cyclone-induced events have occurred at this site in the past after the grounding of Iceberg B9B. Future events may be predictable on synoptic time scales, if cyclone-induced strong wind events can be predicted. PMID:24937550
NASA Astrophysics Data System (ADS)
Nemirovskaya, I. A.; Lisitzin, A. P.; Novigatsky, A. N.; Redzhepova, Z. U.; Dara, O. M.
2016-07-01
Along the transatlantic section from Ushuaia to Gdańsk (March 26-May 7, 2015; cruise 47 of R/V Akademik Ioffe), data were obtained on the concentrations of aerosols in the near-water layer of the atmosphere and of particulate matter in surface waters, as well as of organic compounds within the considered matter (Corg, chlorophyll a, lipids, and hydrocarbons). The concentrations of aerosols amounted to 1237-111 739 particles/L for the fraction of 0.3-1 μm and to 0.02-34.4 μg/m2/day for the matter collected by means of the network procedure. The distribution of aerosols is affected by circumcontinental zoning and by the fluxes from arid areas of African deserts. The maximum concentration of the treated compounds were found in the river-sea frontal area (the runoff of the Colorado River, Argentina), as well as when nearing the coasts, especially in the English Channel.
Cyclone-induced rapid creation of extreme Antarctic sea ice conditions.
Wang, Zhaomin; Turner, John; Sun, Bo; Li, Bingrui; Liu, Chengyan
2014-01-01
Two polar vessels, Akademik Shokalskiy and Xuelong, were trapped by thick sea ice in the Antarctic coastal region just to the west of 144°E and between 66.5°S and 67°S in late December 2013. This event demonstrated the rapid establishment of extreme Antarctic sea ice conditions on synoptic time scales. The event was associated with cyclones that developed at lower latitudes. Near the event site, cyclone-enhanced strong southeasterly katabatic winds drove large westward drifts of ice floes. In addition, the cyclones also gave southward ice drift. The arrival and grounding of Iceberg B9B in Commonwealth Bay in March 2011 led to the growth of fast ice around it, forming a northward protruding barrier. This barrier blocked the westward ice drift and hence aided sea ice consolidation on its eastern side. Similar cyclone-induced events have occurred at this site in the past after the grounding of Iceberg B9B. Future events may be predictable on synoptic time scales, if cyclone-induced strong wind events can be predicted. PMID:24937550
Cyclone-induced rapid creation of extreme Antarctic sea ice conditions
NASA Astrophysics Data System (ADS)
Wang, Zhaomin; Turner, John; Sun, Bo; Li, Bingrui; Liu, Chengyan
2014-06-01
Two polar vessels, Akademik Shokalskiy and Xuelong, were trapped by thick sea ice in the Antarctic coastal region just to the west of 144°E and between 66.5°S and 67°S in late December 2013. This event demonstrated the rapid establishment of extreme Antarctic sea ice conditions on synoptic time scales. The event was associated with cyclones that developed at lower latitudes. Near the event site, cyclone-enhanced strong southeasterly katabatic winds drove large westward drifts of ice floes. In addition, the cyclones also gave southward ice drift. The arrival and grounding of Iceberg B9B in Commonwealth Bay in March 2011 led to the growth of fast ice around it, forming a northward protruding barrier. This barrier blocked the westward ice drift and hence aided sea ice consolidation on its eastern side. Similar cyclone-induced events have occurred at this site in the past after the grounding of Iceberg B9B. Future events may be predictable on synoptic time scales, if cyclone-induced strong wind events can be predicted.
NASA Astrophysics Data System (ADS)
Stein, R.; Niessen, F.; Dittmers, K.; Levitan, M.; Levitan, M.; Schoster, F.; Simstich, J.; Steinke, T.; Stepanets, O.
2001-12-01
Within the framework of the joint German-Russian project on "The Nature of Continental Run-Off from the Siberian Rivers and its Behavior in the Adjacent Arctic Basin (Siberian River Run-Off-SIRRO)", a multidisciplinary expedition with RV "Akademik Boris Petrov" was carried out in the Ob and Yenisei estuaries and the southern Kara Sea in August-September 2001. From the geological point of view, the variability of river discharge in relationship to climate change and the reconstruction of extent and history of glaciation in the southern Kara Sea during Late Quaternary times are major foci of interest. To reach these goals, an intensive sediment ecosounding (2-12 kHz) survey and sediment coring program has been performed. Based on profiling and sediment core data, the following preliminary statements can be given: (1) The extent of the eastern margin of the Barents Sea LGM Ice Sheet between 74 and 78oN can be mapped in detail. Different types of glacial to nonglacial facies can be distinguished. This ice barrier should have strongly influenced river discharge, diverted towards the NE probably into the Voronin Trough. (2) The local LGM (?) ice sheet on Taymyr Peninsula seems to be not connected with the Barents Sea Ice Sheet. (3) Siberian river discharge reached maximum values during the last deglaciation and displays distinct (cyclic) variability during Holocene times. Further detailed evaluation of the sediment echograph profiles as well as detailed sedimentological studies and AMS 14C datings will follow to support these ideas.
NASA Astrophysics Data System (ADS)
Tarakanov, R. Yu.; Gritsenko, A. M.
2014-07-01
The frontal structure in the region south of Africa is investigated on the basis of CTD and SADCP measurements along the SR02 hydrophysical section carried by the R/V Akademik Ioffe in December of 2009 from the Cape of Good Hope to 57° S at the Prime Meridian. Eleven jets of the Antarctic Circumpolar Current (ACC) were revealed along the section. These were six jets of the Subantarctic Current (SAC), three jets of the South Polar Current (SPC), and two jets of the Southern Antarctic Current (SthAC). The jet combining the Weddell Front and the Southern Boundary of the ACC was also revealed. All the jets of the SPC based on the data of direct measurements were joined into a single "superjet." The others were manifested by the local velocity maxima in the surface layer of the ocean. The subtropical water along the section from the Southern Subtropical Front to the Shelf-Slope Front near the African shore was almost completely represented by the Indian Ocean (Agulhas Retroflection) water modified by mixing with the fresher water of the southeastern periphery of the Subtropical Atlantic.
NASA Astrophysics Data System (ADS)
Smirnov, A.; Holben, B. N.; Sakerin, S.; Kabanov, D.; Slutsker, I.; Remer, L. A.; Kahn, R.; Ignatov, A.; Chin, M.; Diehl, T. L.; Mishchenko, M.; Liu, L.; Kucsera, T. L.; Giles, D.; Eck, T. F.; Torres, O.; Kopelevich, O.
2005-12-01
Aerosol optical depth measurements were made in October -December 2004 aboard of R/V Akademik Sergey Vavilov. The cruise area included the Atlantic transect from North Sea to Cape Town and then a crossing in the South Atlantic to Ushuaia, Argentina. The hand-held Microtops II sunphotometer was used to acquire 314 series of measurements spanning 38 days. The sunphotometer was pre-calibrated at the NASA Goddard Space Flight Center against a master sun/sky radiometer instrument of the Aerosol Robotic Network (AERONET). The direct sun measurements were acquired in five spectral channels: 340, 440, 675, 870 and 940 nm. To retrieve aerosol optical depths we applied AERONET processing algorithm (Version 2) to the raw data. Aerosol optical depth values were close to background oceanic conditions (0.04-0.08) in the open oceanic areas not influenced by continental sources. Spectral dependence can be described as almost neutral (Angstrom parameter was less than 0.6), especially in the Southern Atlantic. A notable latitudinal variability of optical depth was observed between 15N and 21S, which was associated with the aerosol transport from Africa. Correlations between optical depth and meteorological parameters were considered and comparison between ship-based measurements and AERONET sites along the cruise track was made. Aerosol optical depths were compared to the global transport model (GOCART) simulations and satellite retrievals from MODIS, MISR, and AVHRR.
Heat flow through the sea bottom around the Yucatan Peninsula
Khutorskoy, M.D.; Kononov, V.I.; Polyak, B.G. ); Fernandez, R. ); Matveev, V.G.; Rot, A.A. )
1990-02-10
Heat flow studies were conducted in January-February 1987, off the Atlantic Coast of Mexico on board the R/V Akademik Nikolai Strakhov. Two areas were surveyed, one transecting the Salt Dome Province and the Campeche Canyon, in the Gulf of Mexico, and the other, on the eastern flank of the Yucatan Peninsula. Conductive heat flow through the bottom sediments was determined as the product of vertical temperature gradient and in situ thermal conductivity, measured with a thermal probe using a multithermistor array and real-time processing capabilities. Forward two-dimensional modeling allows one to estimate heat flow variations at both sites from local disturbances and to obtain average heat flow values of 51 mW/m{sup 2} for the transect within the Gulf of Mexico and 38 and 69 mW/m{sup 2} for two basins within the Yucatan area. Sea bottom relief has a predominant effect over other environmental factors in the scatter of heat flow determination in the Gulf of Mexico.
Drag coefficients for winter Antarctic pack ice
NASA Technical Reports Server (NTRS)
Wamser, Christian; Martinson, Douglas G.
1993-01-01
Air-ice and ice-water drag coefficients referenced to 10-m-height winds for winter Antarctic pack ice based on measurements made from R/V Polarstern during the Winter Weddell Sea Project, 1986 (WWSP-86), and from R/V Akademik Fedorov during the Winter Weddell Gyre Study, 1989 (WWGS-89), are presented. The optimal values of the air-ice drag coefficients, made from turbulent flux measurements, are (1.79 +/- 0.06) x 10 exp -3 for WWSP-86 and (1.45 +/- 0.09) x 10 exp -3 for WWGS-89. A single ice-water drag coefficient for both WWSP-86 and WWGS-89, estimated from periods of ice drift throught to represent free-drift conditions, is (1.13 +/- 0.26) x 10 exp -3, and the ice-water turning angle is 18 +/- 18 deg. It is suggested that for a typical Antarctic winter pack ice cover, the ice cover reduces the momentum flux from the atmosphere to the ocean by about 33 percent.
NASA Astrophysics Data System (ADS)
Baranov, B. V.; Ivashchenko, A. I.; Dozorova, K. A.
2015-12-01
We present a structural study of the Central Kuril Islands forearc region, where the great megathrust tsunamigenic earthquake ( M w 8.3) occurred on November 15, 2006. Based on new bathymetry and seismic profiles obtained during two research cruises of R/V Akademik Lavrentiev in 2005 and 2006, ten crustal segments with along-arc length ranging from 30 to 100 km, separated by NS- and NW-trending transcurrent faults were identified within the forearc region. The transcurrent faults may serve as barriers impeding stress transfer between the neighboring segments, so that stress accumulated within separate forearc segments is usually released by earthquakes of moderate-to-strong magnitudes. However, the great November 15, 2006 earthquake ruptured seven of the crustal segments probably following a 226-year gap since the last great earthquake in 1780. The geographic extent of earthquake rupture zones, aftershock areas and earthquake clusters correlate well with forearc crustal segments identified using the geophysical data. Based on segmented structure of the Central Kuril Islands forearc region, we consider and discuss three scenarios of a great earthquake occurrence within this area. Although the margin is segmented, we suggest that a rupture could occupy the entire seismic gap with a total length of about 500 km. In such a case, the earthquake magnitude M w might exceed 8.5, and such an event might generate tsunami waves significantly exceeding in height to those produced by the great 2006-2007 Kuril earthquakes.
Measuring chlorophyll a concentrations in the Sea of Japan using probe and flow fluorimeters
NASA Astrophysics Data System (ADS)
Zakharkov, S. P.; Shtraikhert, E. A.; Shambarova, Y. V.; Gordeichuk, T. N.; Shi, X.
2016-05-01
The spatial variability of chlorophyll a concentrations was studied from the data of two near-shore expeditions and the cruise of the R/V Akademik M.A. Lavrent'ev in October-November 2010 over the northwestern part of the Sea of Japan. The sections across eddies showed a maximum of chlorophyll a at a depth of 40 m. According to the data from the cruise, the chlorophyll a concentration was maximum in the north of the sea and decreased to the south. In parallel, the procedures for chlorophyll a determination were compared for spectrophotometry with a fluorescence probe and a fluorescence flow system. The probe data of chlorophyll a fluorescence showed a high correlation with the chlorophyll a concentrations by spectrophotometry. On the contrary, data on chlorophyll a concentrations from spectrophotometry did not agree with those from the flow system. It was shown that a fluorimeter in the flow system recorded dissolved organic matter along with the chlorophyll a fluorescence.
Validation of the NOAA/NESDIS satellite aerosol product over the North Atlantic in 1989
NASA Astrophysics Data System (ADS)
Ignatov, Aleksandr M.; Stowe, Larry L.; Sakerin, Sergey M.; Korotaev, Gennady K.
1995-03-01
A validation experiment and resulting potential improvements to the operational satellite optical thickness product at the National Oceanic and Atmospheric Administration/National Environmental Satellite Data and Information Service (NOAA/NESDIS) are presented. An earlier paper described a set of Sun photometer measurements collected from the Soviet R/V Akademik Vernadsky during its cruise in the Atlantic Ocean and Mediterranean Sea from September to December 1989. The accuracy of the Sun photometer aerosol optical thickness was proven acceptable of use as a ground truth standard for validation of the NOAA product. This paper describes the validation methodology and the results of its application to the NOAA 11 satellite product. A systematic underestimation in the operational values by about 35%, relative to the ship truth, is found. Causes for this discrepancy are examined, emphasizing the importance of careful satellite instrument calibration, and a revision of the oceanic reflectance model used in the retrieval algorithm. It is shown that the remaining systematic underestimate in satellite aerosol optical thickness can be attributed only to the aerosol model used in the retrieval. Additional checks of this conclusion using independent data sets are underway. If confirmed, a fundamental revision of the presently used aerosol model would be required. An example of a simple adjustment to the present aerosol model which successfully removes the bias is given, based on the assumption of an absorbing aerosol.
Transport et bruit quantique dans les fils mésoscopiques
NASA Astrophysics Data System (ADS)
Torrès, J.
2002-01-01
Un conducteur quantique est bien caractérisé par sa conductance donnée par la formule de Landauer. Mais le bruit contient davantage d'informations que la conductance : il mesure les fluctuations temporelles du courant autour de sa valeur moyenne. De plus, le signe des corrélations de bruit est lié à la statistique des porteurs de charge. Dans une jonction entre un métal normal et un supraconducteur, le bruit présente une singularité à la fréquence Josephson, signature de la charge 2e des paires de Cooper impliquées dans le transport. Lorsque la tension appliquée est supérieure au gap du supraconducteur, la courbe du bruit exhibe des singularités à plusieurs fréquences auxquelles on peut associer un processus de réflexion ou de transmission. L'analogue fermionique de l'expérience d'Hanbury-Brown et Twiss avec un supraconducteur permet d'observer à la fois des corrélations positives et négatives dans un même système. Maintenir une différence de potentiel entre les deux extrémités d'un fil crée une situation relevant de la thermodynamique hors de l'équilibre. Formellement, on peut se ramener à un calcul à l'équilibre et écrire une théorie des perturbations grâce à la méthode de Keldysh. La théorie des liquides de Luttinger décrit les systèmes unidimensionnels d'électrons en interaction. Le hamiltonien peut se mettre sous forme quadratique grâce à la bosonisation. D'autre part, un liquide de Luttinger chiral constitue un bon modèle des états de bord de l'effet Hall quantique fractionnaire. Grâce au formalisme de Keldysh, on peut retrouver une formule de type Schottky et identifier la charge des quasiparticules de Laughlin.
Nichols, T.D.
1991-04-01
Measured rates of multiphoton ionization (MPI) from the ground state of atomic hydrogen by a linearly polarized, subpicosecond KrF laser pulse at 248 nm wavelength are compared to predictions of lowest-order perturbation theory, Floquet theory, and Keldysh-Faisal-Reiss (KFR) theory with and without Coulomb correction for peak irradiance of 3 {times} 10{sup 12}W/cm{sup 2} to 2 {times} 10{sup 14}W/cm{sup 2}. The Coulomb-corrected Keldysh model falls closest to the measured rates, the others being much higher or much lower. At 5 {times} 10{sup 13}W/cm{sup 2}, the number of ATI electrons decreased by a factor of approximately 40 with each additional photon absorbed. ATI of the molecular hydrogen background and of atoms from photodissociation of the molecules were also observed. The experiment employed a crossed-beam technique at ultrahigh vacuum with an rf-discharge atomic hydrogen source and a magnetic-bottle type electron time-of-flight spectrometer to count the electrons in the different ATI channels separately. The apparatus was calibrated to allow comparison of absolute as well as relative ionization rates to the theoretical predictions. This calibration involved measuring the distribution of irradiance in a focal volume that moved randomly and changed its size from time to time. A data collection system under computer control divided the time-of-flight spectra into bins according to the energy of each laser pulse. This is the first measurement of absolute rates of ATI in atomic hydrogen, and the first measurement of absolute test of MPI in atomic hydrogen without a large factor to account for multiple modes in the laser field. As such, the results of this work are important to the development of ATI theories, which presently differ by orders of magnitude in their prediction of the ionization rates. They are also important to recent calculations of temperatures in laser-heated plasmas, many of which incorporate KFR theory.
NASA Technical Reports Server (NTRS)
Kolnik, Jan; Wang, Yang; Oguzman, Ismail H.; Brennan, Kevin F.
1994-01-01
The electron interband impact-ionization rate for both silicon and gallium arsenide is calculated using an ensemble Monte Carlo simulation with the expressed purpose of comparing different formulations of the interband ionization transition rate. Specifically, three different treatments of the transition rate are examined: the traditional Keldysh formula, a new k-dependent analytical formulation first derived by W. Quade, E. Scholl, and M. Rudan (1993), and a more exact, numerical method of Y. Wang and K. F. Brennan (1994). Although the completely numerical formulation contains no adjustable parameters and as such provides a very reliable result, it is highly computationally intensive. Alternatively, the Keldysh formular, although inherently simple and computationally efficient, fails to include the k dependence as well as the details of the energy band structure. The k-dependent analytical formulation of Quade and co-workers overcomes the limitations of both of these models but at the expense of some new parameterization. It is found that the k-dependent analytical method of Quade and co-workers produces very similar results to those obtained with the completely numerical model for some quantities. Specifically, both models predict that the effective threshold for impact ionization in GaAs and silicon is quite soft, that the majority of ionization events originate from the second conduction band in both materials, and that the transition rate is k dependent. Therefore, it is concluded that the k-dependent analytical model can qualitatively reproduce results similar to those obtained with the numerical model yet with far greater computational efficiency. Nevertheless, there exist some important drawbacks to the k-dependent analytical model of Quade and co-workers: These are that it does not accurately reproduce the quantum yield data for bulk silicon, it requires determination of a new parameter, related physically to the overlap intergrals of the Bloch state which
The Holocene History of Placentia Bay, Newfoundland
NASA Astrophysics Data System (ADS)
Sheldon, Christina; Seidenkrantz, Marit-Solveig; Reynisson, Njáll; Juncker Hansen, Mette; Zilmer Christensen, Eva; Kuijpers, Antoon
2013-04-01
Marine sediments analyzed from cores taken in Placentia Bay, Newfoundland, located in the Labrador Sea, captured oceanographic and climatic changes from the end of the Younger Dryas through the Holocene. Placentia Bay is an ideal site to capture changes in both the south-flowing Labrador Current and the north-flowing Gulf Stream, currents which are closely tied to the strength of the North Atlantic sub-polar gyre and the North Atlantic Oscillation. Changes in the atmospheric and oceanographic circulation patterns in the North Atlantic after the last glacial period are inferred from faunal assemblages, mineralogy and dinoflagellate analyses. During the 2007 Akademik Ioffe cruise, three cores were taken from Placentia Bay: AI07-14G, representing the time period 12.7 to 9.8 cal kyr BP, AI07-10G, covering the period ca. 10.4 cal kya BP to the present, and AI07-12G, representing the last 5.7 cal kya. These cores have been analyzed using several climate proxies, including benthic foraminifera, diatoms, IP25, dinoflagellate cysts and XRF. Together, these cores provide high-resolution records of the changes in climatic conditions over the last ca. 13,000 years in the southern Labrador Sea. After the Younger Dryas ended, the beginning of the warmer early Holocene was recorded by an increase in productivity-linked foraminiferal and diatom assemblages, as well as a drop in the presence of the sea-ice indicator IP25 in core 14G (Pearce et al., 2012). Variability in atmospheric circulation during the Holocene was analyzed in core 12G and used to reconstruct changes in the mode of the North Atlantic Oscillation during the late Holocene by analysis of exotic pollen grains. Sea-surface conditions during the late Holocene in Placentia Bay reflect a decrease in the strength of the Labrador Current, based on warmer sea-surface temperatures and a simultaneous decline in Arctic water export, from ~4000 cal years to ~3000 cal years BP, which falls into the overall large-scale trend of
Nonlinear and Nonequilibrium Spin Injection in Magnetic Tunneling Junctions
NASA Astrophysics Data System (ADS)
Guo, Hong
2007-03-01
Quantitative analysis of charge and spin quantum transport in spintronic devices requires an atomistic first principles approach that can handle nonlinear and nonequilibrium transport conditions. We have developed an approach for this purpose based on real space density functional theory (DFT) carried out within the Keldysh nonequilibrium Green's function formalism (NEGF). We report theoretical analysis of nonlinear and nonequilibrium spin injection and quantum transport in Fe/MgO/Fe trilayer structures as a function of external bias voltage. Devices with well relaxed atomic structures and with FeO oxidization layers are investigated as a function of external bias voltage. We also report calculations of nonequilibrium spin injection into molecular layers and graphene. Comparisons to experimental data will be presented. Work in collaborations with: Derek Waldron, Vladimir Timochevski (McGill University); Ke Xia (Institute of Physics, Chinese Academy of Science, Beijing, China); Eric Zhu, Jian Wang (University of Hong Kong); Paul Haney, and Allan MacDonald (University of Texas at Austin).
Spatial interferences in the electron transport of heavy-fermion materials
NASA Astrophysics Data System (ADS)
Zhang, Shu-feng; Liu, Yu; Song, Hai-Feng; Yang, Yi-feng
2016-08-01
The scanning tunneling microscopy/spectroscopy and the point contact spectroscopy represent major progress in recent heavy-fermion research. Both have revealed important information on the composite nature of the emergent heavy-electron quasiparticles. However, a detailed and thorough microscopic understanding of the similarities and differences in the underlying physical processes of these techniques is still lacking. Here we study the electron transport in the normal state of the periodic Anderson lattice by using the Keldysh nonequilibrium Green's function technique. In addition to the well-known Fano interference between the conduction and f -electron channels, our results further reveal the effect of spatial interference between different spatial paths at the interface on the differential conductance and their interesting interplay with the band features such as the hybridization gap and the Van Hove singularity. We find that the spatial interference leads to a weighted average in the momentum space for the electron transport and could cause suppression of the electronic band features under certain circumstances. In particular, it reduces the capability of probing the f -electron spectral weight near the edges of the hybridization gap for large interface depending on the Fermi surface of the lead. Our results indicate an intrinsic inefficiency of the point contact spectroscopy in probing the f electrons.
Photon assisted tunneling through three quantum dots with spin-orbit-coupling
Tang, Han-Zhao; An, Xing-Tao; Wang, Ai-Kun; Liu, Jian-Jun
2014-08-14
The effect of an ac electric field on quantum transport properties in a system of three quantum dots, two of which are connected in parallel, while the third is coupled to one of the other two, is investigated theoretically. Based on the Keldysh nonequilibrium Green's function method, the spin-dependent current, occupation number, and spin accumulation can be obtained in our model. An external magnetic flux, Rashba spin-orbit-coupling (SOC), and intradot Coulomb interactions are considered. The magnitude of the spin-dependent average current and the positions of the photon assisted tunneling (PAT) peaks can be accurately controlled and manipulated by simply varying the strength of the coupling and the frequency of the ac field. A particularly interesting result is the observation of a new kind of PAT peak and a multiple-PAT effect that can be generated and controlled by the coupling between the quantum dots. In addition, the spin occupation number and spin accumulation can be well controlled by the Rashba SOC and the magnetic flux.
Interactions and thermoelectric effects in a parallel-coupled double quantum dot
NASA Astrophysics Data System (ADS)
Sierra, Miguel A.; Saiz-Bretín, M.; Domínguez-Adame, F.; Sánchez, David
2016-06-01
We investigate the nonequilibrium transport properties of a double quantum-dot system connected in parallel to two leads, including intradot electron-electron interaction. In the absence of interactions, the system supports a bound state in the continuum. This state is revealed as a Fano antiresonance in the transmission when the energy levels of the dots are detuned. Using the Keldysh nonequilibrium Green's-function formalism, we find that the occurrence of the Fano antiresonance survives in the presence of Coulomb repulsion. We give precise predictions for the experimental detection of bound states in the continuum. First, we calculate the differential conductance as a function of the applied voltage and the dot level detuning and find that crossing points in the diamond structure are revealed as minima due to the transmission antiresonances. Second, we determine the thermoelectric current in response to an applied temperature bias. In the linear regime, quantum interference gives rise to sharp peaks in the thermoelectric conductance. Remarkably, we find interaction-induced strong current nonlinearities for large thermal gradients that may lead to several nontrivial zeros in the thermocurrent. The latter property is especially attractive for thermoelectric applications.
Monitoring DNA polymerase with nanotube-based nanocircuits
NASA Astrophysics Data System (ADS)
Li, Yan; Hodak, Miroslav; Lu, Wenchang; Bernholc, Jerry; Collins, Philip
DNA polymerases play an important role in the process of life by accurately and efficiently replicating our genetic information. They use a single-stranded DNA as a template and incorporate nucleotides to create the full, double-stranded DNA. Recent experiments have successfully monitored this process by attaching a Klenow fragment of polymerase I to a carbon nanotube and measuring the current along the tube. Follow-up experiments have shown promise for distinguishing between DNA base pairs when nucleotide analogs are used, thus opening a new avenue for DNA sequencing. In this talk, we present results from computational studies on DNA polymerase I nanocircuits. The enzyme was first equilibrated in molecular dynamics and then density functional theory and Keldysh non-equilibrium Green's function methods were used to calculate the ballistic transmission coefficients and currents for different enzymatic states. Our results show significant change in current when the enzyme alternates between open (idle) and closed (synthesizing) states. We can also differentiate between some template bases when modified nucleotides and gate scanning are used.
Nonequilibrium functional bosonization of quantum wire networks
Ngo Dinh, Stephane; Bagrets, Dmitry A.; Mirlin, Alexander D.
2012-11-15
We develop a general approach to nonequilibrium nanostructures formed by one-dimensional channels coupled by tunnel junctions and/or by impurity scattering. The formalism is based on nonequilibrium version of functional bosonization. A central role in this approach is played by the Keldysh action that has a form reminiscent of the theory of full counting statistics. To proceed with evaluation of physical observables, we assume the weak-tunneling regime and develop a real-time instanton method. A detailed exposition of the formalism is supplemented by two important applications: (i) tunneling into a biased Luttinger liquid with an impurity, and (ii) quantum Hall Fabry-Perot interferometry. - Highlights: Black-Right-Pointing-Pointer A nonequilibrium functional bosonization framework for quantum wire networks is developed Black-Right-Pointing-Pointer For the study of observables in the weak tunneling regime a real-time instanton method is elaborated. Black-Right-Pointing-Pointer We consider tunneling into a biased Luttinger liquid with an impurity. Black-Right-Pointing-Pointer We analyze electronic Fabry-Perot interferometers in the integer quantum Hall regime.
Topological aspects of nonlinear optical responses
NASA Astrophysics Data System (ADS)
Morimoto, Takahiro; Nagaosa, Naoto
There are a variety of nonlinear optical effects including higher harmonic generations, photovoltaic effects, and nonlinear Kerr rotations. A recent remarkable progress in the photovoltaic effect is the high efficiency solar cell action in perovskite oxides without inversion symmetry. The crystal structure lacking inversion replaces the role of artificial structures such as p-n junctions in conventional solar cells. One of the proposed mechanisms for this phenomenon is the shift-current which is supported by a band structure lacking inversion and is related to the Berry connection of Bloch wavefunctions. Motivated by these, we explore topological aspects of the nonlinear optical responses. To this end, we employ the Keldysh method combined with the Floquet formalism, where effective band structures can be defined under an electric field periodic in time. This enables us to describe the shift-current, nonlinear Kerr rotation, photovoltaic effect, and the photo-induced change in the order parameters in a unified fashion. We connect these nonlinear optical responses to topological quantities involving the Berry connection and Berry curvature. It is found that vector fields defined with the Berry connections in the space of momentum and/or parameters govern the nonlinear responses.
The influence of femtosecond laser wavelength on waveguide fabrication inside glass
NASA Astrophysics Data System (ADS)
Hernandez Rueda, Javier; Clarijs, Jasper; van Oosten, Dries; Krol, Denise M.
2016-03-01
We have investigated the permanent refractive index changes inside fused silica glass after laser inscription of waveguides using ultrashort laser pulses at different wavelengths. To this end the laser frequency was detuned using an optical parametric amplifier (OPA) combined with a confocal arrangement (for cleaning the laser Gaussian spatial profile). The suitability for waveguiding and the refractive index changes were inspected by measuring the near- and farfield output profiles of the laser-machined lines using a continuous wave laser at 660 nm. Raman spectroscopy was performed both for tracks of damage and for good optical waveguides. The structural changes were inferred from peak shifts and relative intensity fluctuations associated with representative Raman bands. In fused silica, changes in the 605 cm-1 peak, which is due to 3-membered Si-O ring structures, were monitored. Since the laser photon energy rules the order, k, of the multiphoton absorption in dielectrics, the role of the laser wavelength for waveguide fabrication will be discussed in terms of different powers of the laser intensity (I(r,z)k(λ)) and the Keldysh formalism for strong field ionization (WSFI(λ)).
Theoretical characterisation of point defects on a MoS2 monolayer by scanning tunnelling microscopy.
González, C; Biel, B; Dappe, Y J
2016-03-11
Different S and Mo vacancies as well as their corresponding antisite defects in a free-standing MoS2 monolayer are analysed by means of scanning tunnelling microscopy (STM) simulations. Our theoretical methodology, based on the Keldysh nonequilibrium Green function formalism within the density functional theory (DFT) approach, is applied to simulate STM images for different voltages and tip heights. Combining the geometrical and electronic effects, all features of the different STM images can be explained, providing a valuable guide for future experiments. Our results confirm previous reports on S atom imaging, but also reveal a strong dependence on the applied bias for vacancies and antisite defects that include extra S atoms. By contrast, when additional Mo atoms cover the S vacancies, the MoS2 gap vanishes and a bias-independent bright protrusion is obtained in the STM image. Finally, we show that the inclusion of these point defects promotes the emergence of reactive dangling bonds that may act as efficient adsorption sites for external adsorbates. PMID:26862020
Non-equilibrium conductance through a benzene molecule in the Kondo regime
NASA Astrophysics Data System (ADS)
Tosi, L.; Roura-Bas, P.; Aligia, A. A.
2012-09-01
Starting from exact eigenstates for a symmetric ring, we derive a low-energy effective generalized Anderson Hamiltonian which contains two spin doublets with opposite momenta and a singlet for the neutral molecule. For benzene, the singlet (doublets) represent the ground state of the neutral (singly charged) molecule. We calculate the non-equilibrium conductance through a benzene molecule, doped with one electron or a hole (i.e. in the Kondo regime), and connected to two conducting leads at different positions. We solve the problem using the Keldysh formalism and the non-crossing approximation. When the leads are connected in the para position (at 180°), the model is equivalent to the ordinary impurity Anderson model and its known properties are recovered. For other positions, there is a partial destructive interference in the co-tunneling processes involving the two doublets and, as a consequence, the Kondo temperature and the height and width of the central peak (for bias voltage Vb near zero) of the differential conductance G = dI/dVb (where I is the current) are reduced. In addition, two peaks at finite Vb appear. We study the position of these peaks, the temperature dependence of G and the spectral densities. Our formalism can also be applied to carbon nanotube quantum dots with intervalley mixing.
Energy relaxation rate and its mesoscopic fluctuations in quantum dots
NASA Astrophysics Data System (ADS)
Kozii, Vladyslav A.; Skvortsov, Mikhail A.
2016-08-01
We analyze the applicability of the Fermi-golden-rule description of quasiparticle relaxation in a closed diffusive quantum dot with electron-electron interaction. Assuming that single-particle levels are already resolved but the initial stage of quasiparticle disintegration can still be described by a simple exponential decay, we calculate the average inelastic energy relaxation rate of single-particle excitations and its mesoscopic fluctuations. The smallness of mesoscopic fluctuations can then be used as a criterion for the validity of the Fermi-golden-rule description. Technically, we implement the real-space Keldysh diagram technique, handling correlations in the quasi-discrete spectrum non-perturbatively by means of the non-linear supersymmetric sigma model. The unitary symmetry class is considered for simplicity. Our approach is complementary to the lattice-model analysis of Fock space: though we are not able to describe many-body localization, we derive the exact lowest-order expression for mesoscopic fluctuations of the relaxation rate, making no assumptions on the matrix elements of the interaction. It is shown that for the quasiparticle with the energy ε on top of the thermal state with the temperature T, fluctuations of its energy width become large and the Fermi-golden-rule description breaks down at max { ε , T } ∼ Δ√{ g }, where Δ is the mean level spacing in the quantum dot, and g is its dimensionless conductance.
Phase space representation of quantum dynamics
Polkovnikov, Anatoli
2010-08-15
We discuss a phase space representation of quantum dynamics of systems with many degrees of freedom. This representation is based on a perturbative expansion in quantum fluctuations around one of the classical limits. We explicitly analyze expansions around three such limits: (i) corpuscular or Newtonian limit in the coordinate-momentum representation, (ii) wave or Gross-Pitaevskii limit for interacting bosons in the coherent state representation, and (iii) Bloch limit for the spin systems. We discuss both the semiclassical (truncated Wigner) approximation and further quantum corrections appearing in the form of either stochastic quantum jumps along the classical trajectories or the nonlinear response to such jumps. We also discuss how quantum jumps naturally emerge in the analysis of non-equal time correlation functions. This representation of quantum dynamics is closely related to the phase space methods based on the Wigner-Weyl quantization and to the Keldysh technique. We show how such concepts as the Wigner function, Weyl symbol, Moyal product, Bopp operators, and others automatically emerge from the Feynmann's path integral representation of the evolution in the Heisenberg representation. We illustrate the applicability of this expansion with various examples mostly in the context of cold atom systems including sine-Gordon model, one- and two-dimensional Bose-Hubbard model, Dicke model and others.
Garny, M.; Hohenegger, A.; Kartavtsev, A.; Lindner, M.
2009-12-15
The generation of a baryon asymmetry via leptogenesis is usually studied by means of classical kinetic equations whose applicability to processes in the hot and expanding early universe is questionable. The approximations implied by the state-of-the-art description can be tested in a first-principle approach based on nonequilibrium field theory techniques. Here, we apply the Schwinger-Keldysh/Kadanoff-Baym formalism to a simple toy model of leptogenesis. We find that, within the toy model, medium effects increase the vertex contribution to the CP-violating parameter. At high temperatures it is a few times larger than in vacuum and asymptotically reaches the vacuum value as the temperature decreases. Contrary to the results obtained earlier in the framework of thermal field theory, the corrections are only linear in the particle number densities. An important feature of the Kadanoff-Baym formalism is that it is free of the double-counting problem, i.e. no need for real intermediate state subtraction arises. In particular, this means that the structure of the equations automatically ensures that the asymmetry vanishes in equilibrium. These results give a first glimpse into a number of new and interesting effects that can be studied in the framework of nonequilibrium field theory.
Excitonic effects in 2D semiconductors: Path Integral Monte Carlo approach
NASA Astrophysics Data System (ADS)
Velizhanin, Kirill; Saxena, Avadh
One of the most striking features of novel 2D semiconductors (e.g., transition metal dichalcogenide monolayers or phosphorene) is a strong Coulomb interaction between charge carriers resulting in large excitonic effects. In particular, this leads to the formation of multi-carrier bound states (e.g., excitons, trions and biexcitons), which could remain stable at near-room temperatures and contribute significantly to optical properties of such materials. In my talk, I will report on our recent progress in using the Path Integral Monte Carlo methodology to numerically study properties of multi-carrier bound states in 2D semiconductors. Incorporating the effect of the dielectric confinement (via Keldysh potential), we have investigated and tabulated the dependence of single exciton, trion and biexciton binding energies on the strength of dielectric screening, including the limiting cases of very strong and very weak screening. The implications of the obtained results and the possible limitations of the used model will be discussed. The results of this work are potentially useful in the analysis of experimental data and benchmarking of theoretical and computational models.
Trion formation in monolayer transition metal dichalcogenides
NASA Astrophysics Data System (ADS)
Kezerashvili, Roman Ya.; Tsiklauri, Shalva M.
We present three-body calculations for trions binding energy in monolayer transition metal dichalcogenides using the method of hyperspherical harmonics (HH). In numerical calculations for a proper treatment of Coulomb screening in two dimensions we assume that electrons and holes are interacted via Keldysh potential. The convergences of binding energy calculations for the ground state of the trion as a function of the grand angular momentum are studied. For the trion binding energy in MoS2 we obtain 19.2 mev. This value is remarkably close to the experimental one of 18 meV. A comparison with results of other calculations are presented. We also study solutions of a hyperradial equation in a minimal approximation for the ground angular momentum to examine two regimes: a long range and a short range cases when the inter particle distance is much greater and much less than the screening length. For these cases, we find analytical expressions for the energy and wave function for trion states
Electron-phonon mediated heat flow in disordered graphene
NASA Astrophysics Data System (ADS)
Chen, Wei; Clerk, Aashish A.
2012-09-01
We calculate the heat flux and electron-phonon thermal conductance in a disordered graphene sheet, going beyond a Fermi’s golden rule approach to fully account for the modification of the electron-phonon interaction by disorder. Using the Keldysh technique combined with standard impurity averaging methods in the regime kFl≫1 (where kF is the Fermi wave vector and l is the mean free path), we consider both scalar potential (i.e., deformation potential) and vector-potential couplings between electrons and phonons. We also consider the effects of electronic screening at the Thomas-Fermi level. We find that the temperature dependence of the heat flux and thermal conductance is sensitive to the presence of disorder and screening, and reflects the underlying chiral nature of electrons in graphene and the corresponding modification of their diffusive behavior. In the case of weak screening, disorder enhances the low-temperature heat flux over the clean system (changing the associated power law from T4 to T3), and the deformation potential dominates. For strong screening, both the deformation potential and vector-potential couplings make comparable contributions, and the low-temperature heat flux obeys a T5 power law.
Nonequilibrium noise correlations in a point contact of helical edge states
NASA Astrophysics Data System (ADS)
Lee, Yu-Wen; Lee, Yu-Li; Chung, Chung-Hou
2012-12-01
We investigate theoretically the nonequilibrium finite-frequency current noise in a four-terminal quantum point contact of interacting helical edge states at a finite bias voltage. Special focus is put on the effects of the single-particle and two-particle scattering between the two helical edge states on the fractional charge quasiparticle excitations shown in the nonequilibrium current noise spectra. Via the Keldysh perturbative approach, we find that the effects of the single-particle and the two-particle scattering processes on the current noise depend sensitively on the Luttinger liquid parameter. Moreover, the Fano factors for the auto- and cross correlations of the currents in the terminals are distinct from the ones for tunneling between the chiral edge states in the quantum Hall liquid. The current noise spectra in the single-particle-scattering-dominated and the two-particle-scattering-dominated regime are shown. Experimental implications of our results on the transport through the helical edges in two-dimensional topological insulators are discussed.
Lehmann representation of the nonequilibrium self-energy
NASA Astrophysics Data System (ADS)
Gramsch, Christian; Potthoff, Michael
2015-12-01
It is shown that the nonequilibrium self-energy of an interacting lattice-fermion model has a unique Lehmann representation. Based on the construction of a suitable noninteracting effective medium, we provide an explicit and numerically practicable scheme to construct the Lehmann representation for the self-energy, given the Lehmann representation of the single-particle nonequilibrium Green's function. This is of particular importance for an efficient numerical solution of Dyson's equation in the context of approximations where the self-energy is obtained from a reference system with a small Hilbert space. As compared to conventional techniques to solve Dyson's equation on the Keldysh contour, the effective-medium approach allows us to reach a maximum propagation time, which can be several orders of magnitude longer. This is demonstrated explicitly by choosing the nonequilibrium cluster-perturbation theory as a simple approach to study the long-time dynamics of an inhomogeneous initial state after a quantum quench in the Hubbard model on a 10 ×10 square lattice. We demonstrate that the violation of conservation laws is moderate for weak Hubbard interaction and that the cluster approach is able to describe prethermalization physics.
Spin and charge Nernst effect in a four-terminal quantum dot ring.
Yang, Xi; Zheng, Jun; Li, Chun-Lei; Guo, Yong
2015-02-25
Based on the Keldysh nonequilibrium Green's function technique, we study the spin and charge Nernst effect in a four-terminal quantum dot (QD) ring device, in which the Rashba spin-orbit interaction (RSOI) is taken into the QDs and the magnetic field penetrates the ring. We find that only with the assistance of RSOI, can the pure spin Nernst effect occur by applying a thermal bias without any magnetic field or ferromagnetic materials in the system. Under certain RSOI and magnetic field strengths, spin-down or spin-up currents can be driven from terminal 2 or 4. The sign and the magnitude of the spin currents or voltages can be modulated by adjusting the RSOI-induced phase factor and the magnetic flux. Moreover, the magnitude of the Nernst effect can be remarkably enhanced by the intra-dot Coulomb blockade. The Nernst coefficient is predicted to be more than two times larger than the case of zero Coulomb interaction. Our results indicate that such a four-terminal QD ring may be used as a manipulative thermoelectric generator. PMID:25629548
Guo, Junji; Liao, Wenhu Zhao, Heping; Zhou, Guanghui
2014-01-14
We theoretically investigate the electrically controllable spin polarization and selective efficiency of the edge state Dirac electron in a two-dimensional topological insulator (TI) sandwiched between ferromagnetic (FM) electrodes by using the method of Keldysh nonequilibrium Green's function. A nearly full spin polarization of the topological edge state with giant inversion of ∼80% is observed, which is much higher than the value previously reported. Moreover, the selective efficiency for spin-up electrons under the modulation of the parallel configuration of FM electrodes has been demonstrated to be larger than 95% for the first time, while that for spin-down electrons in the antiparallel case is higher than 90% in a wide energy range, owing to the inter-edge spin tunneling induced backscattering and spin dephasing effect. The obtained results may provide a deeper understanding of the TI edge states and a valuable guidance to design spin switch and filter with high on-off speed and selective efficiency based on TIs.
Wang, Xiaodong; Pan, Ming; Hou, Liwei; Xie, Wei; Hu, Weida Xu, Jintong; Li, Xiangyang; Chen, Xiaoshuang Lu, Wei
2014-01-07
The gain and photoresponse characteristics have been numerically studied for back-illuminated separate absorption and multiplication (SAM) GaN avalanche photodiodes (APDs). The parameters of fundamental models are calibrated by simultaneously comparing the simulated dark and light current characteristics with the experimental results. Effects of environmental temperatures and device dimensions on gain characteristics have been investigated, and a method to achieve the optimum thickness of charge layer is obtained. The dependence of gain characteristics and breakdown voltage on the doping concentration of the charge layer is also studied in detail to get the optimal charge layer. The bias-dependent spectral responsivity and quantum efficiency are then presented to study the photoresponse mechanisms inside SAM GaN APDs. It is found the responsivity peak red-shifts at first due to the Franz-Keldysh effect and then blue-shifts due to the reach-through effect of the absorption layer. Finally, a new SAM GaN/AlGaN heterojunction APD structure is proposed for optimizing SAM GaN APDs.
NASA Astrophysics Data System (ADS)
Dong, B.; Ding, G. H.; Lei, X. L.
2015-05-01
A general theoretical formulation for the effect of a strong on-site Coulomb interaction on the time-dependent electron transport through a quantum dot under the influence of arbitrary time-varying bias voltages and/or external fields is presented, based on slave bosons and the Keldysh nonequilibrium Green's function (GF) techniques. To avoid the difficulties of computing double-time GFs, we generalize the propagation scheme recently developed by Croy and Saalmann to combine the auxiliary-mode expansion with the celebrated Lacroix's decoupling approximation in dealing with the second-order correlated GFs and then establish a closed set of coupled equations of motion, called second-order quantum rate equations (SOQREs), for an exact description of transient dynamics of electron correlated tunneling. We verify that the stationary solution of our SOQREs is able to correctly describe the Kondo effect on a qualitative level. Moreover, a comparison with other methods, such as the second-order von Neumann approach and Hubbard-I approximation, is performed. As illustrations, we investigate the transient current behaviors in response to a step voltage pulse and a harmonic driving voltage, and linear admittance as well, in the cotunneling regime.
Finite-frequency noise in a non-interacting quantum dot
NASA Astrophysics Data System (ADS)
Zamoum, Redouane; Lavagna, Mireille; Crépieux, Adeline
2016-05-01
We calculate the non-symmetrized finite-frequency NS-FF noise for a single-level quantum dot connected to reservoirs in the spinless non-interacting case. The calculations are performed within the framework of the Keldysh Green’s function formalism in the wide band approximation limit. We establish the general formula for NS-FF noise for any values of temperature, frequency and bias voltage. The electron transfer processes from one to the other reservoir act via the transmission amplitude and transmission coefficient depending on the energy. By taking the symmetrized version of this expression, we show that our result coincides with the expression of the finite frequency noise obtained by Büttiker using the scattering theory. We also give the explicit analytical expression for the NS-FF noise in the zero temperature limit. Finally, by performing numerical calculations, we discuss the evolution of the NS-FF noise spectrum with varying temperature, dot energy level, and coupling strength to the reservoirs, revealing a large variety of behaviors such as different symmetry properties and changes of sign in the excess noise.
Analytical description of ballistic spin currents and torques in magnetic tunnel junctions
NASA Astrophysics Data System (ADS)
Chshiev, M.; Manchon, A.; Kalitsov, A.; Ryzhanova, N.; Vedyayev, A.; Strelkov, N.; Butler, W. H.; Dieny, B.
2015-09-01
In this work we demonstrate explicit analytical expressions for both charge and spin currents which constitute the 2 ×2 spinor in magnetic tunnel junctions with noncollinear magnetizations under applied voltage. The calculations have been performed within the free electron model in the framework of the Keldysh formalism and WKB approximation. We demonstrate that spin/charge currents and spin transfer torques are all explicitly expressed through only three irreducible quantities, without further approximations. The conditions and mechanisms of deviation from the conventional sine angular dependence of both spin currents and torques are shown and discussed. It is shown in the thick barrier approximation that all tunneling transport quantities can be expressed in an extremely simplified form via Slonczewski spin polarizations and our effective spin averaged interfacial transmission probabilities and effective out-of-plane polarizations at both interfaces. It is proven that the latter plays a key role in the emergence of perpendicular spin torque as well as in the angular dependence character of all spin and charge transport considered. It is demonstrated directly also that for any applied voltage, the parallel component of spin current at the FM/I interface is expressed via collinear longitudinal spin current components. Finally, spin transfer torque behavior is analyzed in a view of transverse characteristic length scales for spin transport.
Cosmology with many light scalar fields: Stochastic inflation and loop corrections
NASA Astrophysics Data System (ADS)
Adshead, Peter; Easther, Richard; Lim, Eugene A.
2009-03-01
We explore the consequences of the existence of a very large number of light scalar degrees of freedom in the early universe. We distinguish between participator and spectator fields. The former have a small mass, and can contribute to the inflationary dynamics; the latter are either strictly massless or have a negligible VEV. In N-flation and generic assisted inflation scenarios, inflation is a cooperative phenomenon driven by N participator fields, none of which could drive inflation on its own. We review upper bounds on N, as a function of the inflationary Hubble scale H. We then consider stochastic and eternal inflation in models with N participator fields showing that individual fields may evolve stochastically while the whole ensemble behaves deterministically, and that a wide range of eternal inflationary scenarios are possible in this regime. We then compute one-loop quantum corrections to the inflationary power spectrum. These are largest with N spectator fields and a single participator field, and the resulting bound on N is always weaker than those obtained in other ways. We find that loop corrections to the N-flation power spectrum do not scale with N, and thus place no upper bound on the number of participator fields. This result also implies that, at least to leading order, the theory behaves like a composite single scalar field. In order to perform this calculation, we address a number of issues associated with loop calculations in the Schwinger-Keldysh “in-in” formalism.
Quantum dynamical phase transition in a system with many-body interactions
NASA Astrophysics Data System (ADS)
Danieli, E. P.; Álvarez, G. A.; Levstein, P. R.; Pastawski, H. M.
2007-02-01
Recent experiments, [G.A. Álvarez, E.P. Danieli, P.R. Levstein, H.M. Pastawski, J. Chem. Phys. 124 (2006) 194507], have reported the observation of a quantum dynamical phase transition in the dynamics of a spin swapping gate. In order to explain this result from a microscopic perspective, we introduce a Hamiltonian model of a two level system with many-body interactions with an environment whose excitation dynamics is fully solved within the Keldysh formalism. If a particle starts in one of the states of the isolated system, the return probability oscillates with the Rabi frequency ω0. For weak interactions with the environment 1/τ<2ω0, we find a slower oscillation whose amplitude decays with a rate 1/τϕ=1/(2τ). However, beyond a finite critical interaction with the environment, 1/τ>2ω0, the decay rate becomes 1/τϕ∝ω02τ. The oscillation period diverges showing a quantum dynamical phase transition to a Quantum Zeno phase consistent with the experimental observations.
The two Loschmidt daemons and the origin of infidelity
NASA Astrophysics Data System (ADS)
Pastawski, Horacio M.; Danieli, Ernesto P.; Foa Torres, Luis F. F.
2004-03-01
In an open quantum system a local excitation spreads away. Producing a Loschmidt Echo (LE) requires the action of a mechanism called a Loschmidt daemon. An actual realization of one of such creatures, which we dubbed the hasty daemon, is an instantaneous action with global effect: the change in the sign of the Hamiltonian. The chaotic nature of a many-body dynamics produces a fragility to perturbations that degrades the fidelity of the evolution and limits the LE formation [1]. An alternative, the stubborn daemon, is inspired in the acoustic time reversal mirror [2] which through a persistent local action of reinjection of wave function amplitude can produce a backward propagation. Although its theoretical description is not yet fully developed, the procedure is known to be quite robust. We use the Keldysh formalism to prescribe the injection required for a perfect LE. We also use a semiclassical approximation to discuss why chaos in the underlying classical system favors the action of this stubborn daemon.[1] P. R. Levstein, et al. J. Chem. Phys.108, 2718 (1998);[2] A. Tourin, et al. Phys. Rev. Lett. 87, 274301 (2001)
Medium corrections to the CP-violating parameter in leptogenesis
Garny, M.; Hohenegger, A.; Kartavtsev, A.
2010-04-15
In two recent papers, it has been demonstrated that one can obtain quantum-corrected Boltzmann kinetic equations for leptogenesis using a top-down approach based on the Schwinger-Keldysh/Kadanoff-Baym formalism. These 'Boltzmann-like' equations are similar to the ones obtained in the conventional bottom-up approach but differ in important details. In particular there is a discrepancy between the CP-violating parameter obtained in the first-principle derivation and in the framework of thermal field theory. Here we demonstrate that the two approaches can be reconciled if causal n-point functions are used in the thermal field theory approach. The new result for the medium correction to the CP-violating parameter is qualitatively different from the conventional one. The analogy to a toy model considered earlier enables us to write down consistent quantum-corrected Boltzmann equations, for thermal leptogenesis in the standard model extended by three right-handed neutrinos, which include quantum statistical terms and medium-corrected expressions for the CP-violating parameter.
Amundsen, Morten; Linder, Jacob
2016-01-01
An extension of quasiclassical Keldysh-Usadel theory to higher spatial dimensions than one is crucial in order to describe physical phenomena like charge/spin Hall effects and topological excitations like vortices and skyrmions, none of which are captured in one-dimensional models. We here present a numerical finite element method which solves the non-linearized 2D and 3D quasiclassical Usadel equation relevant for the diffusive regime. We show the application of this on three model systems with non-trivial geometries: (i) a bottlenecked Josephson junction with external flux, (ii) a nanodisk ferromagnet deposited on top of a superconductor and (iii) superconducting islands in contact with a ferromagnet. In case (i), we demonstrate that one may control externally not only the geometrical array in which superconducting vortices arrange themselves, but also to cause coalescence and tune the number of vortices. In case (iii), we show that the supercurrent path can be tailored by incorporating magnetic elements in planar Josephson junctions which also lead to a strong modulation of the density of states. The finite element method presented herein paves the way for gaining insight in physical phenomena which have remained largely unexplored due to the complexity of solving the full quasiclassical equations in higher dimensions. PMID:26961921
Electron-photon interaction in a quantum point contact coupled to a microwave resonator
NASA Astrophysics Data System (ADS)
Mendes, Udson C.; Mora, Christophe
2016-06-01
We study a single-mode cavity weakly coupled to a voltage-biased quantum point contact. In a perturbative analysis, the lowest order predicts a thermal state for the cavity photons, driven by the emission noise of the conductor. The cavity is thus emptied as all transmission probabilities of the quantum point contact approach one or zero. Two-photon processes are identified at higher coupling, and pair absorption dominates over pair emission for all bias voltages. As a result, the number of cavity photons, the cavity damping rate, and the second-order coherence g(2 ) are all reduced and exhibit less bunching than the thermal state. These results are obtained with a Keldysh path-integral formulation and reproduced with rate equations. They can be seen as a backaction of the cavity measuring the electronic noise. Extending the standard P (E ) theory to a steady-state situation, we compute the modified noise properties of the conductor and find quantitative agreement with the perturbative calculation.
Spin filtering in a magnetized zigzag phosphorene nanoribbon
NASA Astrophysics Data System (ADS)
Keshtan, M. Ali M.; Esmaeilzadeh, Mahdi
2015-12-01
Using the Keldysh non-equilibrium Green’s function method and applying the Landauer-Büttiker formula, the spin-dependent electron transport properties of a zigzag phosphorene nanoribbon at zero temperature are studied. The depositing of two ferromagnetic strips on the edges of the nanoribbon induces exchange fields with parallel and anti-parallel configurations. An external perpendicular electric field is also applied to manipulate the spin-dependent electron conductance properties. Due to the order of the zigzag phosphorene nanoribbon edge bands near zero Fermi energy, parallel and anti-parallel configurations result in different properties. For anti-parallel configuration, spin filtering only occurs in the presence of a perpendicular electric field, while in the parallel case spin filtering takes place both in the absence and in the presence of an electric field. Although spin filtering properties are invariant against the inversion of the direction of the electric field in a parallel configuration, this inversion changes the spin filtering type for anti-parallel configurations.
Wang Cong; Jiang Lan; Li Xin; Wang Feng; Yuan Yanping; Lu Yongfeng
2013-04-14
We present first-principles calculations for nonlinear photoionization of diamond induced by the intense femtosecond laser field. A real-time and real-space time-dependent density functional theory with the adiabatic local-density approximation is applied to describe the laser-material interactions in the Kohn-Sham formalism with the self-interaction correction. For a certain laser wavelength, the intensity dependence of energy absorption on multiphoton and/or tunnel ionization mechanisms is investigated, where laser intensity regions vary from 10{sup 12} W/cm{sup 2} to 10{sup 16} W/cm{sup 2}. In addition, the effect of laser wavelength on energy absorption at certain ionization mechanism is discussed when the Keldysh parameter is fixed. Theoretical results show that: (1) at the fixed laser wavelength, the relationship between the energy absorption and laser intensity shows a good fit of E = c{sub M}I{sup N} (N is the number of photons absorbed to free from the valence band) when multiphoton ionization dominates; (2) while when tunnel ionization becomes significant, the relationship coincides with the expression of E = c{sub T}I{sup n} (n < N).
Zhang, Qingfang; Liu, Yan; Yan, Jing; Zhang, Chunfu; Hao, Yue; Han, Genquan
2015-03-23
We theoretically investigate a tensile strained GeSn waveguide integrated with Si₃N₄ liner stressor for the applications in mid-infrared (MIR) detector and modulator. A substantial tensile strain is induced in a 1 × 1 μm² GeSn waveguide by the expansion of 500 nm Si₃N₄ liner stressor and the contour plots of strain are simulated by the finite element simulation. Under the tensile strain, the direct bandgap E(G,Γ) of GeSn is significantly reduced by lowering the Γ conduction valley in energy and lifting of degeneracy of valence bands. Absorption coefficients of tensile strained GeSn waveguides with different Sn compositions are calculated. As the Si₃N₄ liner stressor expands by 1%, the cut-off wavelengths of tensile strained Ge(0.97)Sn(0.03), Ge(0.95)Sn(0.05), and Ge(0.90)Sn(0.10) waveguide photodetectors are extended to 2.32, 2.69, and 4.06 μm, respectively. Tensile strained Ge(0.90)Sn(0.10) waveguide electro-absorption modulator based on Franz-Keldysh (FK) effect is demonstrated in theory. External electric field dependence of cut-off wavelength and propagation loss of tensile strained Ge(0.90)Sn(0.10) waveguide is observed, due to the FK effect. PMID:25837129
Amundsen, Morten; Linder, Jacob
2016-01-01
An extension of quasiclassical Keldysh-Usadel theory to higher spatial dimensions than one is crucial in order to describe physical phenomena like charge/spin Hall effects and topological excitations like vortices and skyrmions, none of which are captured in one-dimensional models. We here present a numerical finite element method which solves the non-linearized 2D and 3D quasiclassical Usadel equation relevant for the diffusive regime. We show the application of this on three model systems with non-trivial geometries: (i) a bottlenecked Josephson junction with external flux, (ii) a nanodisk ferromagnet deposited on top of a superconductor and (iii) superconducting islands in contact with a ferromagnet. In case (i), we demonstrate that one may control externally not only the geometrical array in which superconducting vortices arrange themselves, but also to cause coalescence and tune the number of vortices. In case (iii), we show that the supercurrent path can be tailored by incorporating magnetic elements in planar Josephson junctions which also lead to a strong modulation of the density of states. The finite element method presented herein paves the way for gaining insight in physical phenomena which have remained largely unexplored due to the complexity of solving the full quasiclassical equations in higher dimensions. PMID:26961921
Quasiclassical description of a superconductor with a spin density wave
NASA Astrophysics Data System (ADS)
Moor, A.; Volkov, A. F.; Efetov, K. B.
2011-04-01
We derive equations for the quasiclassical Green’s functions ǧ within a simple model of a two-band superconductor with a spin density wave (SDW). The elements of the matrix ǧ are the retarded, advanced, and Keldysh functions, each of which is an 8×8 matrix in the Gor’kov-Nambu, the spin, and the band space. In equilibrium, these equations are a generalization of the Eilenberger equation. On the basis of the derived equations, we analyze the Knight shift, the proximity, and the dc Josephson effects in the superconductors under consideration. The Knight shift is shown to depend on the orientation of the external magnetic field with respect to the direction of the vector of the magnetization of the SDW. The proximity effect is analyzed for an interface between a superconductor with the SDW and a normal metal. The function describing both superconducting and magnetic correlations is shown to penetrate the normal metal or a metal with the SDW due to the proximity effect. The dc Josephson current in an SSDW/N/SSDW junction is also calculated as a function of the phase difference φ. It is shown that in our model, the Josephson current does not depend on the mutual orientation of the magnetic moments in the superconductors SSDW and is proportional to sinφ. The dissipationless spin current jsp depends on the angle α between the magnetization vectors in the same way (jsp~sinα) and is not zero above the superconducting transition temperature.
The excitonic insulator route through a dynamical phase transition induced by an optical pulse
NASA Astrophysics Data System (ADS)
Brazovskii, S.; Kirova, N.
2016-03-01
We consider a dynamical phase transition induced by a short optical pulse in a system prone to thermodynamical instability. We address the case of pumping to excitons whose density contributes directly to the order parameter. To describe both thermodynamic and dynamic effects on equal footing, we adopt a view of the excitonic insulator for the phase transition and suggest a formation of the Bose condensate for the pumped excitons. The work is motivated by experiments in donor-acceptor organic compounds with a neutral- ionic phase transition coupled to the spontaneous lattice dimerization and to charge transfer excitons. The double nature of the ensemble of excitons leads to an intricate time evolution, in particular, to macroscopic quantum oscillations from the interference between the Bose condensate of excitons and the ground state of the excitonic insulator. The coupling of excitons and the order parameter also leads to self-trapping of their wave function, akin to self-focusing in optics. The locally enhanced density of excitons can surpass a critical value to trigger the phase transformation, even if the mean density is below the required threshold. The system is stratified in domains that evolve through dynamical phase transitions and sequences of merging. The new circumstances in experiments and theory bring to life, once again, some remarkable inventions made by L.V. Keldysh.
NASA Astrophysics Data System (ADS)
Rajput, Gagan; Chand, S.; Ahluwalia, P. K.; Sharma, K. C.
2010-10-01
In this paper, we present a theoretical study of correlated electronic transport through coupled double quantum dot (DQD) system attached to normal leads, using a generalised two impurity Anderson Hamiltonian in the presence of intra- and inter-dot Coulomb interactions. A generic formulation from which different structures, i.e. series, symmetric as well as asymmetric parallel and T-shape, can be obtained easily, is developed using Keldysh non-equilibrium Green functions method. The occupation numbers and correlators appearing in the formulation have been calculated in a self-consistent manner. A special attention is paid to investigate the ZBM in the differential conductance, which appears, develops and disappears over a particular range of interdot Coulomb interaction, in the configuration of interest. The ZBM is found to result from the renormalization of energy levels induced by the interdot Coulomb interaction and therefore an attempt has been made to understand it within the framework of local density of states. The interdot tunneling is found to enhance the effect of the interdot Coulomb interaction in inducing the ZBM in all the three configurations. Calculations for the T-shape configuration reveal that non-zero value of the interdot tunneling is an essential condition for the appearance of the ZBM in the differential conductance.
(1)/(N) expansion of the nonequilibrium infinite- U Anderson model
NASA Astrophysics Data System (ADS)
Ratiani, Zurab; Mitra, Aditi
2009-06-01
Results are presented for the nonequilibrium infinite- U Anderson model using a large N approach, where N is the degeneracy of the impurity level, and where nonequilibrium is established by coupling the level to two leads at two different chemical potentials so that there is current flow. A slave-boson representation combined with Keldysh functional integral methods is employed. Expressions for the static spin susceptibility χS and the conductance G are presented to O((1)/(N)) and for an applied voltage difference V less than the Kondo temperature. The correlation function for the slave boson is found to be significantly modified from its equilibrium form in that it acquires a rapid decay in time with a rate that equals the current-induced decoherence rate. Physical observables are found to have a rather complex dependence on the coupling strength to the two leads which can lead to asymmetric behavior χS(V)≠χS(-V) , G(V)≠G(-V) both in the mixed valence and in the Kondo regime.
Photon-assisted electronic and spin transport in a junction containing precessing molecular spin
NASA Astrophysics Data System (ADS)
Filipović, Milena; Belzig, Wolfgang
2016-02-01
We study the ac charge and -spin transport through an orbital of a magnetic molecule with spin precessing in a constant magnetic field. We assume that the source and drain contacts have time-dependent chemical potentials. We employ the Keldysh nonequilibrium Green's functions method to calculate the spin and charge currents to linear order in the time-dependent potentials. The molecular and electronic spins are coupled via exchange interaction. The time-dependent molecular spin drives inelastic transitions between the molecular quasienergy levels, resulting in a rich structure in the transport characteristics. The time-dependent voltages allow us to reveal the internal precession time scale (the Larmor frequency) by a dc conductance measurement if the ac frequency matches the Larmor frequency. In the low-ac-frequency limit the junction resembles a classical electric circuit. Furthermore, we show that the setup can be used to generate dc-spin currents, which are controlled by the molecular magnetization direction and the relative phases between the Larmor precession and the ac voltage.
Majorana transport in superconducting nanowire with Rashba and Dresselhaus spin-orbit couplings
NASA Astrophysics Data System (ADS)
You, Jiabin; Shao, Xiao-Qiang; Tong, Qing-Jun; Chan, A. H.; Oh, C. H.; Vedral, Vlatko
The tunneling experiment is a key technique for detecting Majorana fermion (MF) in solid state systems. We use Keldysh non-equilibrium Green function method to study two-lead tunneling in superconducting nanowire with Rashba and Dresselhaus spin-orbit couplings. A zero-bias dc conductance peak appears in our setup which signifies the existence of MF and is in accordance with previous experimental results on InSb nanowire. Interestingly, due to the exotic property of MF, there exists a hole transmission channel which makes the currents asymmetric at the left and right leads. The ac current response mediated by MF is also studied here. To discuss the impacts of Coulomb interaction and disorder on the transport property of Majorana nanowire, we use the renormalization group method to study the phase diagram of the wire. It is found that there is a topological phase transition under the interplay of superconductivity and disorder. We find that the Majorana transport is preserved in the superconducting-dominated topological phase and destroyed in the disorder-dominated non-topological insulator phase.
Physics at the Moscow State University in 70-th. Photographs
NASA Astrophysics Data System (ADS)
Gaina, Alex B.; Perov, Nikolay S.
The Internet proceeding contains various photographs and autographs of scientists from the Moscow State University, made during 70-th and 80-th years of XX-th Century. While no the album refers to Physics in totality, the main part of the album does refer. It includes photographs and autographs of the Members of the Academy of Sciences of U.S.S.R. Il'ya M. Lifshitz, Alexander I. Ishlinskii, Leonid V. Keldysh, Nobel Prize Winners Vitaly L. Ginzburg and Andrej D. Sakharov, Professors: I.M. Ternov, M.I. Kaganov, V.I. Grigor'ev, V.R. Khalilov, V.Ch. Zhukovskij, V.G. Bagrov (Tomsk State University) and other. Another part of peoples on the photographs became later University professors and Members of Academies. A photo concerns the graduated from the Moscow University, astronomer Vladimir A. Albitzky (1892-1952) made in Odessa during the First World War, while another concerns the School "Quantum Particles in intense fields" held in Chisinau in May 1985.
International scientific optical network for space debris research
NASA Astrophysics Data System (ADS)
Molotov, I.; Agapov, V.; Titenko, V.; Khutorovsky, Z.; Burtsev, Yu.; Guseva, I.; Rumyantsev, V.; Ibrahimov, M.; Kornienko, G.; Erofeeva, A.; Biryukov, V.; Vlasjuk, V.; Kiladze, R.; Zalles, R.; Sukhov, P.; Inasaridze, R.; Abdullaeva, G.; Rychalsky, V.; Kouprianov, V.; Rusakov, O.; Litvinenko, E.; Filippov, E.
A joint team of researchers under the auspices of the Center for Space Debris Information Collection, Processing and Analysis of the Russian Academy of Sciences collaborates with 15 observatories around the world to perform observations of space debris. For this purpose, 14 telescopes were equipped with charge-coupled device (CCD) cameras, Global Positioning System (GPS) receivers, CCD frame processing and ephemeris computation software, with the support of the European and Russian grants. Many of the observation campaigns were carried out in collaboration with the Astronomical Institute of the University of Bern (AIUB) team operating at the Zimmerwald observatory and conducting research for the European Space Agency (ESA), using the Tenerife/Teide telescope for searching and tracking of unknown objects in the geostationary region (GEO). More than 130,000 measurements of space objects along a GEO arc of 340.9°, collected and processed at Space Debris Data Base in the Ballistic Center of the Keldysh Institute of Applied Mathematics (KIAM) in 2005 2006, allowed us to find 288 GEO objects that are absent in the public orbital databases and to determine their orbital elements. Methods of discovering and tracking small space debris fragments at high orbits were developed and tested. About 40 of 150 detected unknown objects of magnitudes 15 20.5 were tracked during many months. A series of dedicated 22-cm telescopes with large field of view for GEO survey tasks is in process of construction. 7 60-cm telescopes will be modernized in 2007.
Strelkov, V. V.
2006-07-15
We present a quantum-mechanical theory of xuv generation by an elliptically polarized intense laser field. Our approach is valid when the Keldysh parameter {gamma} is about unity or less, and the driving ellipticity is less than {radical}(2){gamma}. After the photoionization the motion of the electronic wave packet along the major axis of the driving field polarization ellipse is described quasiclassically, whereas the motion in the transverse direction is considered fully quantum mechanically; we also find the condition that allows the reduction of the motion description to a quantum orbit in the polarization plane of the laser field. We use the ionization rate calculated via numerical solution of the three-dimensional Schroedinger equation (TDSE), and take into account the Coulomb modification of the free electronic wave packet. The predictions of our theory for xuv emission agree well with numerical and experimental results. We study the high harmonic intensities and phases as functions of the driving intensity and ellipticity, and also the ellipticity and the rotation angle of the harmonic field polarization ellipse as functions of the driving ellipticity. The atomic response is decomposed into the contributions of different quantum paths. This allows finding a straightforward explanation for the observed dependencies.
Transient dynamics and waiting time distribution of molecular junctions in the polaronic regime
NASA Astrophysics Data System (ADS)
Seoane Souto, R.; Avriller, R.; Monreal, R. C.; Martín-Rodero, A.; Levy Yeyati, A.
2015-09-01
We develop a theoretical approach to study the transient dynamics and the time-dependent statistics for the Anderson-Holstein model in the regime of strong electron-phonon coupling. For this purpose we adapt a recently introduced diagrammatic approach to the time domain. The generating function for the time-dependent charge transfer probabilities is evaluated numerically by discretizing the Keldysh contour. The method allows us to analyze the system evolution to the steady state after a sudden connection of the dot to the leads, starting from different initial conditions. Simple analytical results are obtained in the regime of very short times. We study in particular the apparent bistable behavior occurring for strong electron-phonon coupling, small bias voltages, and a detuned dot level. The results obtained are in remarkably good agreement with numerically exact results obtained by quantum Monte Carlo methods. We analyze the waiting time distribution and charge transfer probabilities, showing that only a single electron transfer is responsible for the rich structure found in the short-time regime. A universal scaling (independent of the model parameters) is found for the relative amplitude of the higher order current cumulants in the short-time regime, starting from an initially empty dot. We finally analyze the convergence to the steady state of the differential conductance and of the differential Fano factor at the inelastic threshold, which exhibits a peculiar oscillatory behavior.
Anti-Stokes-enhanced tunneling ionization of molecules
NASA Astrophysics Data System (ADS)
Kornev, Aleksei S.; Zon, Boris A.
2012-10-01
We consider the influence of vibrational motion of nuclei on the tunneling ionization of a molecule in a strong light field. Unlike the molecular Ammosov-Delone-Krainov (MO-ADK) model [X. M. Tong , Phys. Rev. APLRAAN1050-294710.1103/PhysRevA.66.033402 66, 033402 (2002)], the Franck-Condon factors that take into consideration the quantization of nuclear vibrations are introduced in the theory. Modification of the vibrational motion of nuclei by the external field leads to the time-dependent constant in the asymptotic form of the electronic wave function. This in turn leads to a more significant modification of the Keldysh theory for the tunnel effect in molecules as compared to the MO-ADK model. We take into account the possibility of vibrational quantum numbers changing in a neutral molecule and in a molecular ion in the process of the tunneling ionization, which in principle enables one to get molecular ions of a certain isotopic composition if the vibrational states of the neutral molecules with this isotopic composition are pumped before ionization. We present numerical results illustrating this possibility for the isotopes of a hydrogen molecule.
Effect of modulating field on photoreflectance simulated by electroreflectance
NASA Astrophysics Data System (ADS)
Chiou, S. J.; Sung, Y. G.; Wang, D. P.; Huang, K. F.; Huang, T. C.; Chu, A. K.
1999-04-01
Photoreflectance (PR) of surface-intrinsic-n+ (s-i-n+) type doped GaAs has been simulated by electroreflectance (ER). The simulated spectra of the s-i-n+ sample have exhibited many Franz-Keldysh oscillations, which enable the electric field (F) to be determined. It is known that F's determined from PR are subjected to photovoltaic effect and the measured F is close to Fbi-δF/2 when the modulating field, δF≪Fbi, where Fbi is the built-in field of the sample and δF is the modulating field. In this work, we have investigated the relation between the measured F and δF not only for the region where δF≪Fbi holds, but also for a whole range of δF. In order to determine the magnitude of δF, we have used ER to simulate PR, that is, the measurements of ER under a forward bias, which is set to be equal to δF/2.
NASA Astrophysics Data System (ADS)
Wang, D. P.; Huang, K. M.; Shen, T. L.; Huang, K. F.; Huang, T. C.
1998-01-01
The electroreflectance (ER) spectra of an undoped-n+ type doped GaAs has been measured at various amplitudes of modulating fields (δF). Many Franz-Keldysh oscillations were observed above the band gap energy, thus enabling the electric field (F) in the undoped layer to be determined. The F is obtained by applying fast Fourier transformation to the ER spectra. When δF is small, the power spectrum can be clearly resolved into two peaks, which corresponds to heavy- and light-hole transitions. When δF is less than ˜1/8 of the built-in field (Fbi˜77 420 V/cm), the F deduced from the ER is almost independent of δF. However, when larger than this, F is increased with δF. Also, when δF is increased to larger than ˜1/8 of Fbi, a shoulder appears on the right side of the heavy-hole peak of the power spectrum. The separation between the main peak and the shoulder of the heavy-hole peak becomes wider as δF becomes larger.
Adiabatic quantum pump in a zigzag graphene nanoribbon junction
NASA Astrophysics Data System (ADS)
Zhang, Lin
2015-11-01
The adiabatic electron transport is theoretically studied in a zigzag graphene nanoribbon (ZGNR) junction with two time-dependent pumping electric fields. By modeling a ZGNR p-n junction and applying the Keldysh Green’s function method, we find that a pumped charge current is flowing in the device at a zero external bias, which mainly comes from the photon-assisted tunneling process and the valley selection rule in an even-chain ZGNR junction. The pumped charge current and its ON and OFF states can be efficiently modulated by changing the system parameters such as the pumping frequency, the pumping phase difference, and the Fermi level. A ferromagnetic ZGNR device is also studied to generate a pure spin current and a fully polarized spin current due to the combined spin pump effect and the valley valve effect. Our finding might pave the way to manipulate the degree of freedom of electrons in a graphene-based electronic device. Project supported by the National Natural Science Foundation of China (Grant No. 110704033), the Natural Science Foundation of Jiangsu Province, China (Grant No. BK2010416), and the Natural Science Foundation for Colleges and Universities in Jiangsu Province, China (Grant No. 13KJB140005).
Dissipation and decoherence effects on a moving particle in front of a dielectric plate
NASA Astrophysics Data System (ADS)
Farías, M. Belén; Lombardo, Fernando C.
2016-03-01
In this work, we consider a particle moving in front of a dielectric plate and study two of the most relevant effects of the vacuum field fluctuations: the dissipation and the decoherence of the particle's internal degrees of freedom. We consider the particle to follow a classical, macroscopically fixed trajectory. To study the dissipative effects, we calculate the in-out effective action by functionally integrating over the vacuum field and the microscopic degrees of freedom of both the plate and the particle. This in-out effective action develops an imaginary part and, hence, a nonvanishing probability for the decay (because of friction) of the initial vacuum state. We analyze how the dissipation is affected by the relative velocity between the particle and the plate and the properties of the microscopic degrees of freedom. In order to study the effects of decoherence over the internal degrees of freedom of the particle, we calculate the closed time path or Schwinger-Keldysh influence action, by functionally integrating over the vacuum field and the microscopic degrees of freedom of the plate. We estimate the decoherence time as the time needed by two different quantum configurations (of the internal degree of freedom of the particle) to be possible to differentiate from one another. We analyze the way in which the presence of the mirror affects the decoherence and the possible ways to maximize or reduce its effects.
NASA Astrophysics Data System (ADS)
Čechavičius, B.; Kavaliauskas, J.; Krivaitė, G.; Seliuta, D.; Valušis, G.; Halsall, M. P.; Steer, M. J.; Harrison, P.
2005-07-01
We present an optical study of beryllium δ-doped GaAs /AlAs multiple quantum well (QW) structures designed for sensing terahertz (THz) radiation. Photoreflectance (PR), surface photovoltage (SPV), and wavelength-modulated differential surface photovoltage (DSPV) spectra were measured in the structures with QW widths ranging from 3to20nm and doping densities from 2×1010to5×1012cm-2 at room temperature. The PR spectra displayed Franz-Keldysh oscillations which enabled an estimation of the electric-field strength of ˜20kV/cm at the sample surface. By analyzing the SPV spectra we have determined that a buried interface rather than the sample surface mainly governs the SPV effect. The DSPV spectra revealed sharp features associated with excitonic interband transitions which energies were found to be in a good agreement with those calculated including the nonparabolicity of the energy bands. The dependence of the exciton linewidth broadening on the well width and the quantum index has shown that an average half monolayer well width fluctuations is mostly predominant broadening mechanism for QWs thinner than 10nm. The line broadening in lightly doped QWs, thicker than 10nm, was found to arise from thermal broadening with the contribution from Stark broadening due to random electric fields of the ionized impurities in the structures. We finally consider the possible influence of strong internal electric fields, QW imperfections, and doping level on the operation of THz sensors fabricated using the studied structures.
NASA Astrophysics Data System (ADS)
Cechavičius, Bronislovas; Kavaliauskas, Julius; Krivaite, Gene; Seliuta, Dalius; Valusis, Gintaras; Halsall, Matthew P.; Steer, Matthew J.; Harrison, Paul
2005-08-01
We measured the photoreflectance (PR) and wavelength-modulated differential surface photovoltage (DSPV) spectra of δ-doped GaAs/AlAs multiple quantum wells (MQW) with different well widths and doping levels. We demonstrated that PR and DSPV are powerful contactless tools for the characterization of MQW structures. We observed Franz-Keldysh oscillations in the PR spectra, which enabled us to determine the built-in electric fields in the GaAs/AlAs MQW structures. As it turned out, in the GaAs buffedcap layers the field strength is in the range of 18-20 kV/cm. It was found that a buried interface rather than the structure surface very probably governs the SPV effect. Sharp features associated with excitonic optical transitions were revealed in both, PR and DSPV spectra. From the line shape analysis of the modulation spectra, we estimated optical transition energies and broadening parameters. The energy levels and interband transition energies calculated by the transfer matrix method are in good agreement with the experimental values. The influence of the doping on the broadening of exciton resonances was observed and investigated.
Reprint of : Block-determinant formalism for an action of a multi-terminal scatterer
NASA Astrophysics Data System (ADS)
Nazarov, Yuli V.
2016-08-01
The scattering theory of electron transport allows for a compact and powerful description in terms of gˇ2 = 1 Green functions, the so-called circuit theory of quantum transport. A scatterer in the theory is characterized by an action, most generally a Keldysh one, that can be further used as a building bock of theories describing statistics of electron transport, superconducting correlations, time-dependent and interaction effects. The action is usually used in the form suitable for a two-terminal scatterer. Here we provide a comprehensive derivation of a more general form of the action that is especially suitable and convenient for general multi-terminal scatterers. The action is expressed as a determinant of a block of the scattering matrix obtained by projection on the positive eigenvalues of the Green functions characterizing the reservoirs. We start with traditional Green function formalism introducing gˇ2 = 1 matrices and give a first example of multi-terminal counting statistics. Further we consider one-dimensional channels and discuss chiral anomaly arising in this context. Generalizing on many channels and superconducting situation, we arrive at the block-determinant relation. We give the necessary elaborative examples reproducing basic results of counting statistics and super-currents in multi-terminal junctions.
Floquet-Boltzmann equation for periodically driven Fermi systems
NASA Astrophysics Data System (ADS)
Genske, Maximilian; Rosch, Achim
2015-12-01
Periodically driven quantum systems can be used to realize quantum pumps, ratchets, artificial gauge fields, and novel topological states of matter. Starting from the Keldysh approach, we develop a formalism, the Floquet-Boltzmann equation, to describe the dynamics and the scattering of quasiparticles in such systems. The theory builds on a separation of time scales. Rapid, periodic oscillations occurring on a time scale T0=2 π /Ω are treated using the Floquet formalism and quasiparticles are defined as eigenstates of a noninteracting Floquet Hamiltonian. The dynamics on much longer time scales, however, is modeled by a Boltzmann equation which describes the semiclassical dynamics of the Floquet quasiparticles and their scattering processes. As the energy is conserved only modulo ℏ Ω , the interacting system heats up in the long-time limit. As a first application of this approach, we compute the heating rate for a cold-atom system, where a periodical shaking of the lattice was used to realize the Haldane model [G. Jotzu et al., Nature (London) 515, 237 (2014)], 10.1038/nature13915.
Rottke, H.; Ludwig, J.; Sandner, W.
1996-09-01
We report multiphoton ionization experiments on H{sub 2} and D{sub 2} molecules at 1053- and 526.5-nm excitation wavelengths in the intensity range 5{times}10{sup 13}{endash}5{times}10{sup 14} W/cm{sup 2}. The intensity dependence of the total ion yield, the dissociation fraction, and the photoelectron spectrum is investigated. At 1053 nm we find a strong isotope effect in the dissociation fraction, whereas at 526.5 nm no such effect is observed. Up to 1{times}10{sup 14} W/cm{sup 2} the photoelectron spectrum at 526.5 nm is dominated by resonant ionization processes via Rydberg states of the molecules. They are shifted into resonance at intensities above {approximately}10{sup 13} W/cm{sup 2}. The spectra show that the potential energy curves of the resonant states must have a shape very similar to the corresponding ionic ones. They are therefore mainly determined by the dipole coupling between the ion core orbitals 1{ital s}{sigma}{sub {ital g}} and 2{ital p}{sigma}{sub {ital u}}. At 1053 nm two photoionization regimes are observed: the multiphoton regime with Keldysh parameter {gamma}{gt}1 showing resonance ionization structures, and the tunnel regime ({gamma}{lt}1) at high intensity. The isotope effect in the dissociation fraction at 1053 nm has no influence on the shape of the corresponding photoelectron spectra at this wavelength. {copyright} {ital 1996 The American Physical Society.}
Non-Markovian Quantum Friction of Bright Solitons in Superfluids.
Efimkin, Dmitry K; Hofmann, Johannes; Galitski, Victor
2016-06-01
We explore the quantum dynamics of a bright matter-wave soliton in a quasi-one-dimensional bosonic superfluid with attractive interactions. Specifically, we focus on the dissipative forces experienced by the soliton due to its interaction with Bogoliubov excitations. Using the collective coordinate approach and the Keldysh formalism, a Langevin equation of motion for the soliton is derived from first principles. The equation contains a stochastic Langevin force (associated with quantum noise) and a nonlocal in time dissipative force, which appears due to inelastic scattering of Bogoliubov quasiparticles off of the moving soliton. It is shown that Ohmic friction (i.e., a term proportional to the soliton's velocity) is absent in the integrable setup. However, the Markovian approximation gives rise to the Abraham-Lorentz force (i.e., a term proportional to the derivative of the soliton's acceleration), which is known from classical electrodynamics of a charged particle interacting with its own radiation. These Abraham-Lorentz equations famously contain a fundamental causality paradox, where the soliton (particle) interacts with excitations (radiation) originating from future events. We show, however, that the causality paradox is an artifact of the Markovian approximation, and our exact non-Markovian dissipative equations give rise to physical trajectories. We argue that the quantum friction discussed here should be observable in current quantum gas experiments. PMID:27314722
Non-Markovian Quantum Friction of Bright Solitons in Superfluids
NASA Astrophysics Data System (ADS)
Efimkin, Dmitry K.; Hofmann, Johannes; Galitski, Victor
2016-06-01
We explore the quantum dynamics of a bright matter-wave soliton in a quasi-one-dimensional bosonic superfluid with attractive interactions. Specifically, we focus on the dissipative forces experienced by the soliton due to its interaction with Bogoliubov excitations. Using the collective coordinate approach and the Keldysh formalism, a Langevin equation of motion for the soliton is derived from first principles. The equation contains a stochastic Langevin force (associated with quantum noise) and a nonlocal in time dissipative force, which appears due to inelastic scattering of Bogoliubov quasiparticles off of the moving soliton. It is shown that Ohmic friction (i.e., a term proportional to the soliton's velocity) is absent in the integrable setup. However, the Markovian approximation gives rise to the Abraham-Lorentz force (i.e., a term proportional to the derivative of the soliton's acceleration), which is known from classical electrodynamics of a charged particle interacting with its own radiation. These Abraham-Lorentz equations famously contain a fundamental causality paradox, where the soliton (particle) interacts with excitations (radiation) originating from future events. We show, however, that the causality paradox is an artifact of the Markovian approximation, and our exact non-Markovian dissipative equations give rise to physical trajectories. We argue that the quantum friction discussed here should be observable in current quantum gas experiments.
Theory of thermal conductivity in the disordered electron liquid
NASA Astrophysics Data System (ADS)
Schwiete, G.; Finkel'stein, A. M.
2016-03-01
We study thermal conductivity in the disordered two-dimensional electron liquid in the presence of long-range Coulomb interactions. We describe a microscopic analysis of the problem using the partition function defined on the Keldysh contour as a starting point. We extend the renormalization group (RG) analysis developed for thermal transport in the disordered Fermi liquid and include scattering processes induced by the long-range Coulomb interaction in the sub-temperature energy range. For the thermal conductivity, unlike for the electrical conductivity, these scattering processes yield a logarithmic correction that may compete with the RG corrections. The interest in this correction arises from the fact that it violates the Wiedemann-Franz law. We checked that the sub-temperature correction to the thermal conductivity is not modified either by the inclusion of Fermi liquid interaction amplitudes or as a result of the RG flow. We therefore expect that the answer obtained for this correction is final. We use the theory to describe thermal transport on the metallic side of the metal-insulator transition in Si MOSFETs.
Developing the OEIC solutions using two section light-emitting transistor
NASA Astrophysics Data System (ADS)
Liang, Shan-Fong; Hsu, Yuan-Fu; Cheng, Gong-Sheng; Wu, Chao-Hsin
2016-02-01
An integrated on-chip optical device composed of a multiple quantum-well light-emitter and photodetector in the lightemitting transistor (LET) platform is fabricated. The two devices are 400 μm in length and electrically isolated by dry etching with 4.9 μm gap. The two facets are formed by cleaving for optical output. In this report, we discuss the characteristics of the two-section device and demonstrate the optical detection by the heterojunction phototransistor (HPT) under different operation points (IB and VCE) and injected optical powers. The collector current of the HPT is 74.88 mA without illumination and 83.87 mA under illumination of 7.46μW at VCE = 3 V and IB = 12 mA, which exhibits 12% increment. The responsivity of the InGaP/GaAs HPT can reach to 711.74 A/W. At the electrical modulation bandwidth of phototransistor fT is enhanced from 1.4 GHz to 1.51 GHz under illumination. This is attributed to the Franz-Keldysh photon-assisted absorption at base-collector junction of light-emitting transistor, which produces additional holes and electrons to enhance the current gain. Through the analysis of small-signal equivalent circuit models, we can show the transit time by de-embedding the circuit parasitic effect. Extracting those parameters can clearly know the thermionic emission lifetime in the quantum well.
Electroreflectance of thin-film solar cells: Simulation and experiment
NASA Astrophysics Data System (ADS)
Huber, Christian; Krämmer, Christoph; Sperber, David; Magin, Alice; Kalt, Heinz; Hetterich, Michael
2015-08-01
Electromodulated reflectance (ER) is a standard characterization method to determine critical points such as the band gap in the band structure of semiconductors. These critical points show up as spectrally narrow features in ER and are typically evaluated using Aspnes's third-derivative functional form. ER spectra of stratified semiconductor systems such as thin-film solar cells, however, are significantly distorted by optical interference due to their layered structure. Furthermore, strong built-in electric fields result in a deviation from the typically assumed low-field conditions. We present here simulations of ER spectra from stratified systems based on transfer matrices using the Franz-Keldysh theory in its general form. For realistic thin-film solar cell conditions, distortions of ER line shapes due to the above-mentioned interferences and strong electric fields appear in the simulations. Furthermore, the results show good agreement with measured ER spectra of a structurally well-characterized Cu (In ,Ga ) Se2 (CIGS) solar cell. Our analysis points out the restrictions on the determination of energetic position and number of critical points from ER spectra of stratified systems.
NASA Astrophysics Data System (ADS)
Janicki, Łukasz; Ramírez-López, Manolo; Misiewicz, Jan; Cywiński, Grzegorz; Boćkowski, Michał; Muzioł, Grzegorz; Chèze, Caroline; Sawicka, Marta; Skierbiszewski, Czesław; Kudrawiec, Robert
2016-05-01
Ga-polar, N-polar, and nonpolar m-plane GaN UN+ structures have been examined in air and vacuum ambient by contactless electroreflectance (CER). This technique is very sensitive to the surface electric field that varies with the Fermi level position at the surface. For UN+ GaN structures [i.e., GaN (undoped)/GaN (n-type)/substrate], a homogeneous built-in electric field is expected in the undoped GaN layer that is manifested by Franz–Keldysh oscillation (FKO) in CER spectra. A clear change in FKO has been observed in CER spectra for N-polar and nonpolar m-plane structures when changing from air to vacuum ambient. This means that those surfaces are very sensitive to ambient atmosphere. In contrast to that, only a small change in FKO can be seen in the Ga-polar structure. This clearly shows that the ambient sensitivity of the Fermi level position at the GaN surface varies with the crystallographic orientation and is very high for N-polar and nonpolar m-plane surfaces. This feature of the N-polar and nonpolar m-plane surfaces can be very important for GaN-based devices grown on these crystallographic orientations and can be utilized in some of the devices, e.g., sensors.
Renormalization group analysis of thermal transport in the disordered Fermi liquid
NASA Astrophysics Data System (ADS)
Schwiete, G.; Finkel'stein, A. M.
2014-10-01
We present a detailed study of thermal transport in the disordered Fermi liquid with short-range interactions. At temperatures smaller than the impurity scattering rate, i.e., in the diffusive regime, thermal conductivity acquires nonanalytic quantum corrections. When these quantum corrections become large at low temperatures, the calculation of thermal conductivity demands a theoretical approach that treats disorder and interactions on an equal footing. In this paper, we develop such an approach by merging Luttinger's idea of using gravitational potentials for the analysis of thermal phenomena with a renormalization group calculation based on the Keldysh nonlinear sigma model. The gravitational potentials are introduced in the action as auxiliary sources that couple to the heat density. These sources are a convenient tool for generating expressions for the heat density and its correlation function from the partition function. Already in the absence of the gravitational potentials, the nonlinear sigma model contains several temperature-dependent renormalization group charges. When the gravitational potentials are introduced into the model, they acquire an independent renormalization group flow. We show that this flow preserves the phenomenological form of the correlation function, reflecting its relation to the specific heat and the constraints imposed by energy conservation. The main result of our analysis is that the Wiedemann-Franz law holds down to the lowest temperatures even in the presence of disorder and interactions and despite the quantum corrections that arise for both the electric and thermal conductivities.
Computational investigation of CNT-based DNA polymerase nanocircuits
NASA Astrophysics Data System (ADS)
Li, Yan; Hodak, Miroslav; Lu, Wenchang; Bernholc, Jerry; Collins, Philip
2015-03-01
DNA polymerases are important enzymes that replicate DNA molecules with very low error rates - about one error in 105 bases. Recently, it was found that the replication process can be electrically monitored by attaching a Klenow fragment of polymerase I to the surface of a carbon nanotube and monitoring the current along the tube [1]. In this talk, we report results from computational studies on DNA polymerase nanocircuits. We have first performed classical molecular dynamics (MD) calculations to get snapshots of different enzymatic stages, particularly the open state (no DNA binding) and the closed state (DNA double helix binding). We then used density functional theory (DFT) and Keldysh non-equilibrium Green's function (NEGF) formalism to calculate transmission coefficients and currents for each enzymatic state. Our results show that the transmission spectrum and the currents change significantly when the enzyme moves from the open to the closed state. While the initial experiments did not show signal differences between dissimilar bases, the theoretical work in progress is investigating conditions where bases might have distinct signatures, which would allow for DNA sequencing.
NASA Astrophysics Data System (ADS)
Alvarez, Gonzalo A.
2007-05-01
The control of open quantum systems has a fundamental relevance for fields ranging from quantum information processing to nanotechnology. Typically, the system whose coherent dynamics one wants to manipulate, interacts with an environment that smoothly degrades its quantum dynamics. Thus, a precise understanding of the inner mechanisms of this process, called "decoherence", is critical to develop strategies to control the quantum dynamics. In this thesis we solved the generalized Liouville-von Neumann quantum master equation to obtain the dynamics of many-spin systems interacting with a spin bath. We also solve the spin dynamics within the Keldysh formalism. Both methods lead to identical solutions and together gave us the possibility to obtain numerous physical predictions that contrast well with Nuclear Magnetic Resonance experiments. We applied these tools for molecular characterizations, development of new numerical methodologies and the control of quantum dynamics in experimental implementations. But, more important, these results contributed to fundamental physical interpretations of how quantum dynamics behaves in open systems. In particular, we found a manifestation of an environmentally induced quantum dynamical phase transition.
NASA Technical Reports Server (NTRS)
Hammer, J. M.
1982-01-01
Both the linear electro-optic (Pockel's) effect and electroabsorption (Franz-Keldysh effect) in waveguiding junctions of InGaAsP were measured. The electro-optic coefficient is found to be 0.1-0.14x10 to the -12 power m/V at lambda = 1.54 - 1.65 micrometers. Possibly this is the first reported measurement of the electro-optic coefficient for InGaAsP. The value found for the electroabsorption is on the order of 7x10 to the -4 power cm to the -1 power/(V/cm) or approximately 100 cm/1 for fields of 200,000 V/cm at lambda 1.3 micrometers. All measurements were made on a quaternary film with a bandgap wavelength of 1.23 micrometers. Because of the rapid commercial introduction of quaternary lasers, LEDs, and detectors to take advantage of large optical fiber bandwidths and low losses in the 1.2- to 1.7- micrometer region, these measurements are significant in providing some of the basic physical constants needed to design modulators and switches capable of operating at microwave frequencies in this wavelength region.
Effective equilibrium theory of nonequilibrium quantum transport
NASA Astrophysics Data System (ADS)
Dutt, Prasenjit; Koch, Jens; Han, Jong; Le Hur, Karyn
2011-12-01
The theoretical description of strongly correlated quantum systems out of equilibrium presents several challenges and a number of open questions persist. Here, we focus on nonlinear electronic transport through an interacting quantum dot maintained at finite bias using a concept introduced by Hershfield [S. Hershfield, Phys. Rev. Lett. 70 2134 (1993)] whereby one can express such nonequilibrium quantum impurity models in terms of the system's Lippmann-Schwinger operators. These scattering operators allow one to reformulate the nonequilibrium problem as an effective equilibrium problem associated with a modified Hamiltonian. In this paper, we provide a pedagogical analysis of the core concepts of the effective equilibrium theory. First, we demonstrate the equivalence between observables computed using the Schwinger-Keldysh framework and the effective equilibrium approach, and relate Green's functions in the two theoretical frameworks. Second, we expound some applications of this method in the context of interacting quantum impurity models. We introduce a novel framework to treat effects of interactions perturbatively while capturing the entire dependence on the bias voltage. For the sake of concreteness, we employ the Anderson model as a prototype for this scheme. Working at the particle-hole symmetric point, we investigate the fate of the Abrikosov-Suhl resonance as a function of bias voltage and magnetic field.
Li, Xin; Rong, Wenlong; Jiang, Lan; Zhang, Kaihu; Li, Cong; Cao, Qiang; Zhang, Guangming; Lu, Yongfeng
2014-12-01
We experimentally showed that the π/2-period oscillation of an ablation area with laser polarization direction can be observed in GaAs, ZnSe, MgO and LiF with cubic crystal by a femtosecond laser (800 nm, 100 fs) and that the modulation in the ablation area can be controlled by the laser fluence. While the polarization dependence is sustained in a wide range of laser fluences for a narrow band-gap crystal, it is strongly suppressed with a slight augmentation of laser fluence in a wide band-gap material. The polarization-dependent ablation is explained by the crystal's orientation-dependent reduced-electron mass and the resultant contrasting nonlinear absorptions with slightly different reduced electron mass. The interplay between photoionization and avalanche ionization is discussed to interpret the influence of laser fluence on polarization-dependent ablation. Based on Keldysh's theory, polarization-dependent ablation occurs in a mixed regime between tunneling and multiphoton ionization. PMID:25606947
Photon-assisted tunneling through a topological superconductor with Majorana bound states
Tang, Han-Zhao; Zhang, Ying-Tao; Liu, Jian-Jun
2015-12-15
Employing the Keldysh Nonequilibrium Green’s function method, we investigate time-dependent transport through a topological superconductor with Majorana bound states in the presence of a high frequency microwave field. It is found that Majorana bound states driven by photon-assisted tunneling can absorb(emit) photons and the resulting photon-assisted tunneling side band peaks can split the Majorana bound state that then appears at non-zero bias. This splitting breaks from the current opinion that Majorana bound states appear only at zero bias and thus provides a new experimental method for detecting Majorana bound states in the Non-zero-energy mode. We not only demonstrate that the photon-assisted tunneling side band peaks are due to Non-zero-energy Majorana bound states, but also that the height of the photon-assisted tunneling side band peaks is related to the intensity of the microwave field. It is further shown that the time-varying conductance induced by the Majorana bound states shows negative values for a certain period of time, which corresponds to a manifestation of the phase coherent time-varying behavior in mesoscopic systems.
Low-energy theory of transport in Majorana wire junctions
NASA Astrophysics Data System (ADS)
Zazunov, A.; Egger, R.; Levy Yeyati, A.
2016-07-01
We formulate and apply a low-energy transport theory for hybrid quantum devices containing junctions of topological superconductor (TS) wires and conventional normal (N) or superconducting (S) leads. We model TS wires as spinless p -wave superconductors and derive their boundary Keldysh Green's function, capturing both the Majorana end state and continuum quasiparticle excitations in a unified manner. We also specify this Green's function for a finite-length TS wire. Junctions connecting different parts of the device are described by the standard tunneling Hamiltonian. Using this Hamiltonian approach, one also has the option to include many-body interactions in a systematic manner. For N-TS junctions, we provide the current-voltage (I -V ) characteristics at arbitrary junction transparency and give exact results for the shot-noise power and the excess current. For TS-TS junctions, analytical results for the thermal noise spectrum and for the I -V curve in the high-transparency low-bias regime are presented. For S-TS junctions, we compute the entire I -V curve and clarify the conditions for having a finite Josephson current.
Theoretical characterisation of point defects on a MoS2 monolayer by scanning tunnelling microscopy
NASA Astrophysics Data System (ADS)
González, C.; Biel, B.; Dappe, Y. J.
2016-03-01
Different S and Mo vacancies as well as their corresponding antisite defects in a free-standing MoS2 monolayer are analysed by means of scanning tunnelling microscopy (STM) simulations. Our theoretical methodology, based on the Keldysh nonequilibrium Green function formalism within the density functional theory (DFT) approach, is applied to simulate STM images for different voltages and tip heights. Combining the geometrical and electronic effects, all features of the different STM images can be explained, providing a valuable guide for future experiments. Our results confirm previous reports on S atom imaging, but also reveal a strong dependence on the applied bias for vacancies and antisite defects that include extra S atoms. By contrast, when additional Mo atoms cover the S vacancies, the MoS2 gap vanishes and a bias-independent bright protrusion is obtained in the STM image. Finally, we show that the inclusion of these point defects promotes the emergence of reactive dangling bonds that may act as efficient adsorption sites for external adsorbates.
Effect of oxidation on interlayer exchange coupling in Fe|MgO|Fe tunnel junctions
NASA Astrophysics Data System (ADS)
Yang, H.-X.; Chshiev, M.; Kalitsov, A.; Schuhl, A.; Butler, W. H.
2010-03-01
The interlayer exchange coupling (IEC) in MgO-based magnetic tunnel junctions (MTJ) is a subject of major interest for spintronics community [1,2]. Recent experiments demonstrated that oxydation conditions strongly affect the character of the IEC in Fe/MgO/Fe(001) MTJs [3]. In order to elucidate the effect of over- and under-oxidation on the nature of the IEC in Fe|MgO|Fe MTJs, we performed systematic studies of the influence of O impurities and vacancies on the IEC using ab-initio and tight-binding approaches. We found that the O vacancies cause strong AF IEC in agreement with previous studies [2-4]. Furthermore, an additional O atom at the Fe|MgO interface makes the IEC ferromagnetic in for 3ML and above MgO thicknesses in agreement with experiment [3]. We demonstrate also that the full structural relaxation of ideal Fe|MgO|Fe MTJs may lead to the antiferromagnetic IEC. Tight-binding calculations of the IEC in the framework of the Keldysh formalism were also performed. The results obtained support our first principles calculations. [1] J. Faure-Vincent et al, Phys. Rev. Lett. 89, 107206 (2002); [2] T. Katayama et al., Appl. Phys. Lett. 89, 112503 (2006); [3] Y.F. Chiang et al, Phys. Rev. B 79, 184410 (2009); [4] M.Y. Zhuravlev et al, Phys. Rev. Lett. 94, 026806 (2005).
Non-Markovian Effects in the Lindblad Master Equation Approach to Electronic Transport
NASA Astrophysics Data System (ADS)
Ribeiro, P.; Vieira, V. R.
Non-equilibrium processes in open quantum systems can be generically described within the framework of the Lindblad master equation i.e. without a memory kernel. This statement holds even for processes where information can flow-back from the environment to the system. This rather contra-intuitive fact lead to define a process as non Markovian if, during the time evolution of two different initial states of the system, their distinguishability increases, reflecting a back-flow of information from the environment to the system. However, for non Markovian dynamics, the set of conditions to ensure the positivity of the density matrix for all times is not known, making difficult the explicit construction of non Markovian Lindblad operators. Using the Keldysh non equilibrium Green's functions, we explicitly solve a generic quadratic model of electrons coupled at t = 0 to a set of wide-band baths characterized by temperature and chemical potential. We identify the equivalent Lindblad operators describing the evolution of the density matrix and show that the resulting dynamical process is generically non Markovian. We further discuss the cases in which Markovian dynamics is recovered. We apply our approach to a simple model for electronic transport thought a one dimensional wire coupled at t = 0 to wide-band metallic leads, and to a XY spin chain attached to two contacts.
NASA Astrophysics Data System (ADS)
de Melo, Pedro Miguel M. C.; Marini, Andrea
2016-04-01
We present a full ab initio description of the coupled out-of-equilibrium dynamics of photons, phonons, and electrons. In the present approach, the quantized nature of the electromagnetic field as well as of the nuclear oscillations is fully taken into account. The result is a set of integrodifferential equations, written on the Keldysh contour, for the Green's functions of electrons, phonons, and photons where the different kinds of interactions are merged together. We then concentrate on the electronic dynamics in order to reduce the problem to a computationally feasible approach. By using the generalized Baym-Kadanoff ansatz and the completed collision approximation, we introduce a series of efficient but controllable approximations. In this way, we reduce all equations to a set of decoupled equations for the density matrix that describe all kinds of static and dynamical correlations. The final result is a coherent, general, and inclusive scheme to calculate several physical quantities: carrier dynamics, transient photoabsorption, and light emission, all of which include, at the same time, electron-electron, electron-phonon, and electron-photon interactions. We further discuss how all these observables can be easily calculated within the present scheme using a fully atomistic ab initio approach.
Non-equilibrium STLS approach to transport properties of single impurity Anderson model
NASA Astrophysics Data System (ADS)
Rezai, Raheleh; Ebrahimi, Farshad
2014-04-01
In this work, using the non-equilibrium Keldysh formalism, we study the effects of the electron-electron interaction and the electron-spin correlation on the non-equilibrium Kondo effect and the transport properties of the symmetric single impurity Anderson model (SIAM) at zero temperature by generalizing the self-consistent method of Singwi, Tosi, Land, and Sjolander (STLS) for a single-band tight-binding model with Hubbard type interaction to out of equilibrium steady-states. We at first determine in a self-consistent manner the non-equilibrium spin correlation function, the effective Hubbard interaction, and the double-occupancy at the impurity site. Then, using the non-equilibrium STLS spin polarization function in the non-equilibrium formalism of the iterative perturbation theory (IPT) of Yosida and Yamada, and Horvatic and Zlatic, we compute the spectral density, the current-voltage characteristics and the differential conductance as functions of the applied bias and the strength of on-site Hubbard interaction. We compare our spectral densities at zero bias with the results of numerical renormalization group (NRG) and depict the effects of the electron-electron interaction and electron-spin correlation at the impurity site on the aforementioned properties by comparing our numerical result with the order U2 IPT. Finally, we show that the obtained numerical results on the differential conductance have a quadratic universal scaling behavior and the resulting Kondo temperature shows an exponential behavior.
Block-determinant formalism for an action of a multi-terminal scatterer
NASA Astrophysics Data System (ADS)
Nazarov, Yuli V.
2015-11-01
The scattering theory of electron transport allows for a compact and powerful description in terms of gˇ2 = 1 Green functions, the so-called circuit theory of quantum transport. A scatterer in the theory is characterized by an action, most generally a Keldysh one, that can be further used as a building bock of theories describing statistics of electron transport, superconducting correlations, time-dependent and interaction effects. The action is usually used in the form suitable for a two-terminal scatterer. Here we provide a comprehensive derivation of a more general form of the action that is especially suitable and convenient for general multi-terminal scatterers. The action is expressed as a determinant of a block of the scattering matrix obtained by projection on the positive eigenvalues of the Green functions characterizing the reservoirs. We start with traditional Green function formalism introducing gˇ2 = 1 matrices and give a first example of multi-terminal counting statistics. Further we consider one-dimensional channels and discuss chiral anomaly arising in this context. Generalizing on many channels and superconducting situation, we arrive at the block-determinant relation. We give the necessary elaborative examples reproducing basic results of counting statistics and super-currents in multi-terminal junctions.
NASA Astrophysics Data System (ADS)
Dmitrenko, O. B.; Lukashina, N. P.; Os'kina, N. S.
2012-04-01
The foraminiferal (planktonic and benthic) and nannofosssil assemblages have been analyzed in the sediments of Core ACB-17-1447 taken from the South America continental slope north of the Rio Grande Rise piedmont during Cruise 17 of the R/V Akademik Sergey Vavilov. The core section is largely composed of carbonate and marly hemipelagic mud. The Quaternary age of the host sediments is evident from the occurrence of the planktonic foraminiferal index species Globorotalia truncatulinoides. Based on the nannofossil assemblages, the core sediments are attributed to the upper Pleistocene-Holocene. They contain abundant reworked Pliocene, Miocene, and Paleogene taxa transported from the slopes of the underwater Rio Grande Rise. The paleotemperature analysis of the planktonic foraminifers provided data for constructing the temperature curve that demonstrates two warm peaks. During the first warm period (Interval of 7-9 cm), the surface water temperature was as high as 26°C (Holocene optimum), which exceeds by 3-4°C its presentday values and implies the more intense warm Brazil Current. The earlier warm peak with temperatures up to 24°C recorded in the upper Pleistocene sediments (Interval of 69-71 cm) most likely reflects the 3rd oxygenisotope stage (MIS 3), which corresponds to the interstadial phase of the last glaciation (30-40 ka ago). Based on the abundances, taxonomic diversity, and proportions of the characteristic species of benthic foraminifers, the Core ASV-17-1447 section is divided into six intervals correlated with the marine isotopic stages defined by both the planktonic foraminifers and climatic changes evident from the variations in the bottom water circulation along the southwestern slope of the Brazilian Basin during the Late Quaternary.
NASA Astrophysics Data System (ADS)
Brandt, A.; Elsner, N.; Brenke, N.; Golovan, O.; Malyutina, M. V.; Riehl, T.; Schwabe, E.; Würzberg, L.
2013-02-01
Faunistic data from a newly designed camera-epibenthic sledge (C-EBS) are presented. These were collected during the joint Russian-German expedition SoJaBio (Sea of Japan Biodiversity Studies) on board the R.V. Akademik Lavrentyev from four transects (A-D) between 460 and 3660 m depth. In total, 244,531 macro- and megafaunal individuals were sampled with the classes Malacostraca (80,851 individuals), Polychaeta (36,253 ind.) and Ophiuroidea (34,004 ind.) being most abundant. Within the Malacostraca, Peracarida (75,716 ind.) were most abundant and within these, the Isopoda were the dominant taxon (27,931 ind.), followed by Amphipoda (21,403 ind.), Cumacea (13,971 ind.) and Tanaidacea (10,830 ind.). Mysidacea (1581 ind.) were least frequent. Bivalvia, Amphipoda, Cumacea and Mysidacea as well as inbenthic meiofaunal Nematoda occurred in higher numbers at the shallower stations and their numbers decreased with increasing depth. Polychaeta, Isopoda, and Tanaidacea, on the contrary, increased in abundance with increasing depth. Only one isopod species was sampled at abyssal depths in the Sea of Japan but at very high abundance: Eurycope spinifrons Gurjanova, 1933 (Asellota: Munnopsidae). Echinoderms occurred frequently at the shallower slope stations. Ophiuroids were dominating, followed by holothurians, and echinoids and asteroids which occurred in lower numbers and primarily at the shallower stations of transects A and B. Only 2163 individual anthozoans were recorded and these were mostly confined to the lower slope. The technical design of a new C-EBS is described. Next to temperature-insulated epi- and suprabenthic samplers, it is equipped with still and video cameras, which deliver information on seabed topography and megafaunal occurrence. Furthermore, Aanderaa CTD and SEAGUARD RCM allow for collection of physical parameters, such as near bottom oxygen composition, temperature and conductivity.
NASA Astrophysics Data System (ADS)
Lizunov, G.; Yampolski, Yu.; Korepanov, V.; Lytvynenko, L.; Zalizovsky, A.
The impact of meteorological processes upon the ionosphere cannot be ignored in conceptual space weather models. The giant energy stored in motion of tropospheric air masses (weather fronts, cyclones, stream jets, penetrating convection, etc) serves as a powerful source of upward energy fluxes propagating from the lower to upper atmosphere. The prospective energy carrier might be associated with the middle-scale atmospheric gravity waves (AGW) traveling upwards to the ionospheric heights and producing the effects known as traveling ionospheric disturbances (TID's). We present the results of detailed experimental and theoretical study of these phenomena. The original data had been provided by experiments in the region of high meteorological activity, namely Antarctic coast of the Drake Passage, where the Ukrainian Antarctic station " Akademik Vernadsky" is located (UK's "Michael Faraday" till 1996). The permanent data sets were collected over the seven years from 1996 till 2002. The passing atmospheric fronts were in most cases accompanied by excitation of middle-scale AGW's and quasiperiodic variations of magnetic field components, showing the same time periods as the atmospheric pressure. As follows from the cross-correlation analysis of the magnetic field and pressure variations, the magnetic field normally lagged behind the pressure by few tens minutes. On this base we elaborate a quantitative model describing the AGW excitation by weather fronts, AGW propagation to the upper atmosphere and generation of geomagnetic pulsation in the ionospheric dynamo-region. We expect to carry out further experiments onboard Ukrainian remote sensing satellite "Sich-1M" (launch in 2004), which payload contains optical and radar equipment allowing to detect weather systems as well as a set of electromagnetic sensors ("Variant" experiment" for registration of the fine structure of fields and currents in the ionosphere. We are going to compare a ground based meteorological and
NASA Astrophysics Data System (ADS)
Komatsu, Kensuke; Tachibana, Yoshihiro; Alexeev, Vladimir
2016-04-01
In summer 2013, we conducted 6 hourly radiosonde observation between off-ice and on-ice by Russian icebreaker "Akademik Fedorov" passing through the marginal ice-zone in Laptev Sea during NABOS project (Nansen and Amundsen Basins Obsevational System). During observation period, the warmer and humid air mass was advected by southeasterly wind from Siberia to Laptev sea because the low-pressure system was passing The temperature profiles bellow 600 m was maintaining the cold pool associated with a sea ice and the inversion layer formed above it. The humidity profiles were, however, not trapped until the height of inversion layer, they reached at higher levels (< 5000 m). These observational evidences implied that the humid air from Siberia was lifted on the cold pool maintained by sea ice and this process could transport the moisture to upper level in the arctic region. To verify these processes and examine the impact of the existence of sea ice, we conducted the numerical experiment by WRF. Three boundary conditions were adopted to simulation; present sea ice, removed all sea ice, and increased sea ice area. As primary results, the trajectories of air parcel from Siberia was rising to upper level with released the latent heat due to the condensation of humid air. The case of present sea ice transported much moisture vertically in the arctic region than other two cases. More detail results will be reported on the day. The process of the vertical moisture lifting due to the cold pool could contribute to the heat transport from the mid-latitude surface to the upper level in the arctic.
Seamounts Identified By High-Resolution Imagery Offshore Kenya
NASA Astrophysics Data System (ADS)
Henderson, J. F.; Kagasi, J.; Gikuhi, M.; Njuguna, S.
2008-12-01
Multibeam bathymetry and 2-D seismic reflection surveys were carried out between 2007 and 2008 by the Government of Kenya for the purpose of delineating Kenya's extended continental shelf beyond the 200 nautical mile boundary, as allowed under Article 76 of the United Nations Convention on the Law of the Sea (UNCLOS). The unique dataset acquired includes areas surveyed for the first time and provides new information on the geological processes of the continental shelf, slope and abyssal plain along the Kenyan passive margin. High-resolution multibeam bathymetry of almost the entire Kenyan continental slope was acquired using two multibeam systems (Kongsberg Simrad EM120 and EM710) aboard the M/V L'Espoir in November/December 2007. A multi-channel seismic survey followed in April/May 2008 (R/V Akademik Alexander Karpinsky) and provided high-resolution seismic reflection profiles. During these surveys, three features interpreted to be seamounts were discovered along Kenya's continental slope at water depths between 2750 and 3500 m. The size of the features varies from 2.5 to 10 km in diameter and 570 to 1740 m in height. The Davie Fracture Zone, a north-south trending transform fault was also identified in the seismic reflection profiles. The ridge, possibly extending from 26°S off south Madagascar to as far north as 2°S, is thought to have been created by the separation and direction of motion of Madagascar from Africa that began in the middle Jurassic. The discovery of these features and the integration of both multibeam bathymetry and seismic reflection profiles provides new information in the study of seamount distribution and their relationship to nearby transform faults.
Chemical investigations of Atlantis II and discovery brines in the Red Sea
NASA Astrophysics Data System (ADS)
Danielsson, Lars-Göran; Dyrssen, David; Granéli, Anders
1980-12-01
Analytical data for the Atlantis II and Discovery deeps in the Red Sea are given. The data were collected in March and June 1976 during the 22nd cruise of R/V Akademik Kurchatov in the Indian Ocean. On board analyses were performed of density, chlorinity, Mg, Ca, Sr and trace elements. The salinity, calculated from the density, is related to the chlorinity by S = 1.67 Cl + 4.02. The Ca-salinity relation is linear for both deeps showing that intermediate waters are formed by mixing of the brines with Red Sea water (RSDW). The hot brine (62°C) in the Atlantis II deep contains approx. 80 mg/kg of Fe and Mn while the warm brine (45°C) in the Discovery deep has a very low concentration of Fe and approx. 50 mg/kg of Mn. Mixing of RSDW containing 2 ml/l of oxygen with the anoxic deep brines causes precipitation of hydrous Mn(IV) and Fe(III) hydroxides. These two processes occur at different depths in the two deeps due to the formation of the warm (48-49°) intermediate brine in the Atlantis II deep. The oxidation-hydrolysis reactions proposed are supported by alkalinity-depth profiles and measurements of pH. These reactions also explain most of the trace element distributions and the composition of the SiO 2-Fe(III) hydroxide slurry recovered by some water samplers in the Atlantis II deep.
The Australasian Antarctic Expedition 2013-2014: Practicing 'Citizen-Science' in a Changing World
NASA Astrophysics Data System (ADS)
Fogwill, C. J.; Turney, C. S.
2014-12-01
Government funding is the cornerstone of modern science. But with declining investment in science across most of the Western World, a major challenge for society is where best to place what little resource we have. Which research questions should have the greatest priority? Nowhere are these issues more pressing than in the Antarctic, where bases have and continue to play host to 'big-science', multi-year programmes of research, locking up logistical support and costs. But in a warming world, the areas with the greatest effects of climate change aren't always near government research stations. With this in mind, in 2012 a plan was formed to visit Commonwealth Bay, a remote area off the East Antarctic Ice Sheet, where in 2010, an iceberg the size of Rhode Island, known as B09B, dramatically knocked a 60-mile long tongue of ice off the Mertz Glacier into the Southern Ocean, setting off a cascade of change. Inspired by the expeditions of the past, we advertised berths for sale to take citizen scientists south with us, harnessing their interest, experience and investment. People responded far and wide. We were oversubscribed, and the Australasian Antarctic Expedition 2013-2014 was born. With the Russian-owned MV Akademik Shokalskiy as the expedition vessel, we set out south from the New Zealand port of Bluff in late November 2013. During our journey south and on the ice we undertook a number of scientific firsts for the region actively engaging the volunteer scientists on board in projects ranging from oceanography, biology, ecology, geology and glaciaology. The expedition demostrated how private funding could support targeted programmes of research and communicate it to the wider world. Small-science research can capture the public's imagination and also reap real scientific outputs. Although it is a funding model developed in the Antarctic a hundred years ago, the beauty is it can applied anywhere in the world.
Precipitation Ground Validation over the Oceans
NASA Astrophysics Data System (ADS)
Klepp, C.; Bakan, S.
2012-04-01
State-of-the-art satellite derived and reanalysis based precipitation climatologies show remarkably large differences in detection, amount, variability and temporal behavior of precipitation over the oceans. The uncertainties are largest for light precipitation within the ITCZ and for cold season high-latitude precipitation including snowfall. Our HOAPS (Hamburg Ocean Atmosphere Parameters and Fluxes from Satellite data, www.hoaps.org) precipitation retrieval exhibits fairly high accuracy in such regions compared to our ground validation data. However, the statistical basis for a conclusive validation has to be significantly improved with comprehensive ground validation efforts. However, existing in-situ instruments are not designed for precipitation measurements under high wind speeds on moving ships. To largely improve the ground validation data basis of precipitation over the oceans, especially for snow, the systematic data collection effort of the Initiative Pro Klima funded project at the KlimaCampus Hamburg uses automated shipboard optical disdrometers, called ODM470 that are capable of measuring liquid and solid precipitation on moving ships with high accuracy. The main goal of this project is to constrain the precipitation retrievals for HOAPS and the new Global Precipitation Measurement (GPM) satellite constellation. Currently, three instruments are long-term mounted on the German research icebreaker R/V Polarstern (Alfred Wegner Institut) since June 2010, on R/V Akademik Ioffe (P.P.Shirshov Institute of Oceanology, RAS, Moscow, Russia) since September 2010 and on R/V Maria S. Merian (Brise Research, University of Hamburg) since December 2011. Three more instruments will follow shortly on further ships. The core regions for these long-term precipitation measurements comprise the Arctic Ocean, the Nordic Seas, the Labrador Sea, the subtropical Atlantic trade wind regions, the Caribbean, the ITCZ, and the Southern Oceans as far south to Antarctica. This
11-year solar cycle in Schumann resonance data as observed in Antarctica
NASA Astrophysics Data System (ADS)
Nickolaenko, A. P.; Koloskov, A. V.; Hayakawa, M.; Yampolski, Yu. M.; Budanov, O. V.; Korepanov, V. E.
2015-03-01
Studies of Schumann resonance allows obtaining characteristics of the lower ionosphere and the dynamics of global thunderstorms based on the data recorded at a single or a few ground-based observatories. We use the simple model of a point source. The vertical profile of air conductivity is described by the "knee" model. We used continuous Schumann resonance record from the "Akademik Vernadsky" Ukrainian Antarctic station (geographic coordinates: 65.25S and 64.25W, L=2.6). A data processing show that the north-south seasonal drift of global thunderstorms was about 20°, and the intensity of global lightning activity changed annually by the factor 1.5-2. Unequal duration of the "electromagnetic" seasons was confirmed ("summer" ~ 120 days, "winter" ~ 60 days; duration of the "spring" is shorter than the "fall"). A possible explanation of inter-annual variations of Schumann resonance parameter follows from changes in the effective height of the lower ionosphere. In this case, we used the spatial thunderstorm distribution following from the annual data of the Optical Transient Detector satellite. We show that recorded inter-annual variations of resonance frequencies and intensities might be attributed to 1-2 km alterations in the knee height of ionosphere. The most realistic mechanism of changes should include both the height variations and the drift of global thunderstorms. Both the processes are governed by solar activity. We also estimated the feasible trend in the equatorial soil surface temperature by 1.6° C corresponding to the inter-annual change of Schumann resonance intensity.
NASA Astrophysics Data System (ADS)
Tishchenko, P. Ya.; Talley, L. D.; Lobanov, V. B.; Nedashkovskii, A. P.; Pavlova, G. Yu.; Sagalaev, S. G.
2007-06-01
According to the results of the international expedition aboard the R/Vs Roger Revelle and Professor Khromov in the summer 1999, areas with low oxygen contents (below 210 μM/kg) and those with increased contents of dissolved inorganic carbon and phosphates were found that roughly coincided with one another. These areas are located near the bottom on the southwestern slope of the Tsushima Basin in the region of the Korea Strait and on the continental slope in the region of the Tatar Strait in the northern part of the sea at about 46° N. The set of hydrochemical data points to a high geochemical activity in the near-bottom layer of the areas noted. This activity is confirmed by direct observations of the composition of the interstitial water in the sediments collected in the northern part of the sea during the expedition of R/V Akademik M.A. Lavrent’ev in 2003. It was supposed that the main cause of the increased geochemical activity is the runoff of suspended and dissolved matter from the Korea and Tatar straits. In the areas mentioned, the near-bottom waters are characterized by low values of the nitrogen-phosphorus ratio (below 10), which is geochemical proof of the denitrification process occurring under the conditions of high oxygen concentrations characteristic of the Sea of Japan. Based on the value of the annual production in the Sea of Japan, a rate of denitrification equal to 3.4 × 1012 gN/year was calculated. Hence, it is confirmed that the geochemical processes in the near-bottom layer have a direct influence on the spatiotemporal characteristics of the hydrochemical properties of the waters of the Sea of Japan.
Quasi-Fermi level splitting and sub-bandgap absorptivity from semiconductor photoluminescence
Katahara, John K.; Hillhouse, Hugh W.
2014-11-07
A unified model for the direct gap absorption coefficient (band-edge and sub-bandgap) is developed that encompasses the functional forms of the Urbach, Thomas-Fermi, screened Thomas-Fermi, and Franz-Keldysh models of sub-bandgap absorption as specific cases. We combine this model of absorption with an occupation-corrected non-equilibrium Planck law for the spontaneous emission of photons to yield a model of photoluminescence (PL) with broad applicability to band-band photoluminescence from intrinsic, heavily doped, and strongly compensated semiconductors. The utility of the model is that it is amenable to full-spectrum fitting of absolute intensity PL data and yields: (1) the quasi-Fermi level splitting, (2) the local lattice temperature, (3) the direct bandgap, (4) the functional form of the sub-bandgap absorption, and (5) the energy broadening parameter (Urbach energy, magnitude of potential fluctuations, etc.). The accuracy of the model is demonstrated by fitting the room temperature PL spectrum of GaAs. It is then applied to Cu(In,Ga)(S,Se){sub 2} (CIGSSe) and Cu{sub 2}ZnSn(S,Se){sub 4} (CZTSSe) to reveal the nature of their tail states. For GaAs, the model fit is excellent, and fitted parameters match literature values for the bandgap (1.42 eV), functional form of the sub-bandgap states (purely Urbach in nature), and energy broadening parameter (Urbach energy of 9.4 meV). For CIGSSe and CZTSSe, the model fits yield quasi-Fermi leveling splittings that match well with the open circuit voltages measured on devices made from the same materials and bandgaps that match well with those extracted from EQE measurements on the devices. The power of the exponential decay of the absorption coefficient into the bandgap is found to be in the range of 1.2 to 1.6, suggesting that tunneling in the presence of local electrostatic potential fluctuations is a dominant factor contributing to the sub-bandgap absorption by either purely electrostatic (screened Thomas-Fermi) or
Serendipitous discoveries in nonlocal gravity theory
NASA Astrophysics Data System (ADS)
Barvinsky, A. O.
2012-05-01
We present a class of generally covariant nonlocal gravity models which have a flat-space general relativistic limit and also possess a stable de Sitter or anti-de Sitter (AdS) background with an arbitrary value of its cosmological constant. The nonlocal action of the theory is formulated in the Euclidean signature spacetime and is understood as an approximation to the quantum effective action (generating functional of one-particle irreducible diagrams) originating from fundamental quantum gravity theory. Using the known relation between the Schwinger-Keldysh technique for quantum expectation values and the Euclidean quantum field theory we derive from this action the causal effective equations of motion for mean value of the metric field in the physical Lorentzian-signature spacetime. Thus we show that the (A)dS background of the theory carries as free propagating modes massless gravitons having two polarizations identical to those of the Einstein theory with a cosmological term. The on-shell action of the theory is vanishing both for the flat-space and (A)dS backgrounds which play the role of stable vacua underlying, respectively, the ultraviolet and infrared phases of the theory. We also obtain linearized gravitational potentials of compact matter sources and show that in the infrared (A)dS phase their effective gravitational coupling Geff can be essentially different from the Newton gravitational constant GN of the short-distance general relativistic phase. When Geff≫GN the (A)dS phase can be regarded as a strongly coupled infrared modification of Einstein theory not only describing the dark energy mechanism of cosmic acceleration but also simulating the dark matter phenomenon by enhanced gravitational attraction at long distances.
Large-time evolution of an electron in photon bath
Kazakov, Kirill A.; Nikitin, Vladimir V.
2012-12-15
The problem of infrared divergence of the effective electromagnetic field produced by elementary charges is revisited using the model of an electron freely evolving in a photon bath. It is shown that for any finite travel time, the effective field of the electron is infrared-finite, and that at each order of perturbation theory the radiative contributions grow unboundedly with time. Using the Schwinger-Keldysh formalism, factorization of divergent contributions in multi-loop diagrams is proved, and summation of the resulting infinite series is performed. It is found that despite the unbounded growth of individual contributions to the effective field, their sum is bounded, tending to zero in the limit of infinite travel time. It is concluded that the physical meaning of infrared singularity in the effective field is the existence of a peculiar irreversible spreading of electric charges, caused by their interaction with the electromagnetic field. This spreading originates from the quantum electromagnetic fluctuations, rather than the electron-photon scattering, and exists in vacuum as well as at finite temperatures. It shows itself in a damping of the off-diagonal elements of the momentum-space density matrix of electron, but does not affect its momentum probability distribution. This effect is discussed in terms of thermalization of the electron state, and the asymptotic growth of its quantum entropy is determined. Relationship of the obtained results to the Bloch-Nordsieck theorem is established and considered from the standpoint of measurability of the electromagnetic field. The effect of irreversible spreading on the electron diffraction in the classic two-slit experiment is determined, and is shown to be detectable in principle by modern devices already at room temperature. - Highlights: Black-Right-Pointing-Pointer Infrared finiteness of the effective electromagnetic field of a free electron is proved. Black-Right-Pointing-Pointer Quantum radiative effects
NASA Astrophysics Data System (ADS)
Dai, Hui
The first chapter of the thesis looks at the asymptotics of eigenvalues and eigenvectors of Toeplitz matrices as the size of the matrix, N, goes to infinity. We specialize to the Fisher-Hartwig matrices with real alpha and beta and 0 < alpha < |beta| < 1. Both numerical calculations and an asymptotic analysis using Wiener-Hopf methods indicate that for large N, the jth component of the lth eigenvector varies roughly in the fashion ln ylj ≈ iplj + O(1/ N). The lth wave vector, pl, varies as I pl=2pl/N+i2a +1lnN/N+O1/N for negative values of beta and values of l/(N - 1) not too close to zero or one. Correspondingly the lth eigenvalue is given by IIe l=aexp-ipl +o1/N where a is the Fourier transform (also called the symbol) of the Toeplitz matrix. In the second chapter of this thesis, we study the non-equilibrium transport properties of a one-dimensional (1D) array of dissipative quantum dots. Using the Keldysh formalism, we show that the dots' dissipative nature leads to a spatial variation of the chemical potential, which in disordered arrays, breaks the invariance of the current, I, under bias reversal. We also show that a local Coulomb interaction splits the dots' electronics levels, resulting in a Coulomb blockade, which is softened with increasing dissipation and array size. The third chapter shows studies of the current patterns in 2D nanostructures. We demonstrate that in the weak hopping limit, the 2D nanostructures is equivalent to a classical bedspring resistor network. While in the strong hopping limit, the nanostructures are highly non-local and the current pattern can be explained by their equilibrium energy structures.
Real-time finite-temperature correlators from AdS/CFT
NASA Astrophysics Data System (ADS)
Barnes, Edwin; Vaman, Diana; Wu, Chaolun; Arnold, Peter
2010-07-01
In this paper we use anti-de Sitter/conformal field theory correspondence ideas in conjunction with insights from finite-temperature real-time field theory formalism to compute 3-point correlators of N=4 super Yang-Mills operators, in real time and at finite temperature. To this end, we propose that the gravity field action is integrated only over the right and left quadrants of the Penrose diagram of the anti-de Sitter-Schwarzschild background, with a relative sign between the two terms. For concreteness we consider the case of a scalar field in the black hole background. Using the scalar field Schwinger-Keldysh bulk-to-boundary propagators, we give the general expression of a 3-point real-time Green’s correlator. We then note that this particular prescription amounts to adapting the finite-temperature analog of Veltman’s circling rules to tree-level Witten diagrams, and comment on the retarded and Feynman scalar bulk-to-boundary propagators. We subject our prescription to several checks: Kubo-Martin-Schwinger identities, the largest time equation, and the zero-temperature limit. When specializing to a particular retarded (causal) 3-point function, we find a very simple answer: the momentum-space correlator is given by three causal (two advanced and one retarded) bulk-to-boundary propagators, meeting at a vertex point which is integrated from spatial infinity to the horizon only. This result is expected based on analyticity, since the retarded n-point functions are obtained by analytic continuation from the imaginary-time Green’s function, and based on causality considerations.
Wavelength dependence of femtosecond laser-induced damage threshold of optical materials
Gallais, L. Douti, D.-B.; Commandré, M.; Batavičiūtė, G.; Pupka, E.; Ščiuka, M.; Smalakys, L.; Sirutkaitis, V.; Melninkaitis, A.
2015-06-14
An experimental and numerical study of the laser-induced damage of the surface of optical material in the femtosecond regime is presented. The objective of this work is to investigate the different processes involved as a function of the ratio of photon to bandgap energies and compare the results to models based on nonlinear ionization processes. Experimentally, the laser-induced damage threshold of optical materials has been studied in a range of wavelengths from 1030 nm (1.2 eV) to 310 nm (4 eV) with pulse durations of 100 fs with the use of an optical parametric amplifier system. Semi-conductors and dielectrics materials, in bulk or thin film forms, in a range of bandgap from 1 to 10 eV have been tested in order to investigate the scaling of the femtosecond laser damage threshold with the bandgap and photon energy. A model based on the Keldysh photo-ionization theory and the description of impact ionization by a multiple-rate-equation system is used to explain the dependence of laser-breakdown with the photon energy. The calculated damage fluence threshold is found to be consistent with experimental results. From these results, the relative importance of the ionization processes can be derived depending on material properties and irradiation conditions. Moreover, the observed damage morphologies can be described within the framework of the model by taking into account the dynamics of energy deposition with one dimensional propagation simulations in the excited material and thermodynamical considerations.
Modeling ion sensing in molecular electronics
NASA Astrophysics Data System (ADS)
Chen, Caroline J.; Smeu, Manuel; Ratner, Mark A.
2014-02-01
We examine the ability of molecules to sense ions by measuring the change in molecular conductance in the presence of such charged species. The detection of protons (H+), alkali metal cations (M+), calcium ions (Ca2+), and hydronium ions (H3O+) is considered. Density functional theory (DFT) is used within the Keldysh non-equilibrium Green's function framework (NEGF) to model electron transport properties of quinolinedithiol (QDT, C9H7NS2), bridging Al electrodes. The geometry of the transport region is relaxed with DFT. The transport properties of the device are modeled with NEGF-DFT to determine if this device can distinguish among the M+ + QDT species containing monovalent cations, where M+ = H+, Li+, Na+, or K+. Because of the asymmetry of QDT in between the two electrodes, both positive and negative biases are considered. The electron transmission function and conductance properties are simulated for electrode biases in the range from -0.5 V to 0.5 V at increments of 0.1 V. Scattering state analysis is used to determine the molecular orbitals that are the main contributors to the peaks in the transmission function near the Fermi level of the electrodes, and current-voltage relationships are obtained. The results show that QDT can be used as a proton detector by measuring transport through it and can conceivably act as a pH sensor in solutions. In addition, QDT may be able to distinguish among different monovalent species. This work suggests an approach to design modern molecular electronic conductance sensors with high sensitivity and specificity using well-established quantum chemistry.
Study of optical properties of GaAsN layers prepared by molecular beam epitaxy
NASA Astrophysics Data System (ADS)
Pulzara-Mora, A.; Cruz-Hernández, E.; Rojas-Ramirez, J.; Contreras-Guerrero, R.; Meléndez-Lira, M.; Falcony-Guajardo, C.; Aguilar-Frutis, M. A.; López-López, M.
2007-04-01
We have grown GaAsN layers (with nitrogen concentration between 1.2% and 3.2%) on GaAs(1 0 0) substrates by molecular beam epitaxy (MBE) using a radio frequency (RF) plasma nitrogen source, and solid sources for Ga and As. The growth temperature was varied from 420 to 600 °C, and the GaAsN growth mode was in situ monitored by reflection high-energy electron diffraction (RHEED). The optical properties of the layers were studied by photoreflectance spectroscopy (PR) and phase modulated ellipsometry (PME). For the growth temperature of 420 °C the films grew in a three-dimensional (3D) mode as indicated by the appearance of transmission spots in the RHEED patterns. In contrast, GaAsN layers grown at higher temperatures presented a two-dimensional (2D) growth mode. These GaAsN layers are pseudomorphic according to high-resolution X-ray diffraction (HRXRD). The PR spectra of all samples exhibited Franz-Keldysh oscillations (FKO) above of the GaAs band gap energy. From these oscillations we obtained the built-in internal electric field intensity ( Fint) at the GaAsN/GaAs interface. In the low-energy region of the PR spectra we observed the transitions associated to fundamental band gap of the GaAsN layers. The variation of the GaAsN fundamental band gap obtained by PR as a function of the N content was explained according the band anti-crossing model (BAC). On the other hand, the E1 and E1+Δ E1 critical points were obtained from the analysis of spectra of the imaginary part of the dielectric function obtained by PME. We observed a shift of these critical points to higher energies with the increase of N content, which was explained by a combination of strain and alloying effects.
Comparative study of H(2s) and H(2p0) ionization dynamics in the over-barrier regime
NASA Astrophysics Data System (ADS)
Song, Shu-Na; Geng, Ji-Wei; Jiang, Hong-Bing; Peng, Liang-You
2014-05-01
We investigate theoretically the ionization dynamics of H(2s) and H(2p0) by short midinfrared laser pulses in the over-barrier ionization (OBI) regime. Through the numerical solution to the time-dependent Schrödinger equation, we calculate the differential and angular distributions of photoelectrons as well as the total ionization probability. In a wide range of laser intensities and wavelengths, significant differences are found between the H(2s) and H(2p0) states in both the differential and total ionization yields. Analysis of the excitation dynamics reveals that both the low-lying excited states and the Rydberg states are significantly populated for a 1200-nm laser. As the laser wavelength gradually increases to 2100 nm, the population on the low-lying excited state drastically decreases. We observe the population of the Rydberg states oscillates as a function of the laser peak intensity, which gradually disappears when the Keldysh parameter γ decreases. As the laser intensity increases further, the total ionization probability and the population of the Rydberg states stay almost the same, which is related to the partial stabilization phenomena recently confirmed in experiments. In the deep OBI regime, we find that this kind of ionization suppression is more obvious in the 2s state than in the 2p0 state. We also compare the transverse momentum distributions of the electrons ionized from the two states and find the effect of the Coulomb potential is stronger in the 2p0 state than that in the 2s state, which is due to the different initial electron distributions.
Dynamics and universality in noise-driven dissipative systems
NASA Astrophysics Data System (ADS)
Dalla Torre, Emanuele G.; Demler, Eugene; Giamarchi, Thierry; Altman, Ehud
2012-05-01
We investigate the dynamical properties of low-dimensional systems, driven by external noise sources. Specifically we consider a resistively shunted Josephson junction and a one-dimensional quantum liquid in a commensurate lattice potential, subject to 1/f noise. In absence of nonlinear coupling, we have shown previously that these systems establish a nonequilibrium critical steady state [Dalla Torre, Demler, Giamarchi, and Altman, Nat. Phys.1745-247310.1038/nphys1754 6, 806 (2010)]. Here, we use this state as the basis for a controlled renormalization group analysis using the Keldysh path integral formulation to treat the nonlinearities: the Josephson coupling and the commensurate lattice. The analysis to first order in the coupling constant indicates transitions between superconducting and localized regimes that are smoothly connected to the respective equilibrium transitions. However, at second order, the back action of the mode coupling on the critical state leads to renormalization of dissipation and emergence of an effective temperature. In the Josephson junction, the temperature is parametrically small allowing to observe a universal crossover between the superconducting and insulating regimes. The I-V characteristics of the junction displays algebraic behavior controlled by the underlying critical state over a wide range. In the noisy one-dimensional liquid, the generated dissipation and effective temperature are not small as in the junction. We find a crossover between a quasilocalized regime dominated by dissipation and another dominated by temperature. However, since in the thermal regime the thermalization rate is parametrically small, signatures of the nonequilibrium critical state may be seen in transient dynamics.
Applications of many-body physics to relativistic heavy ion collisions
NASA Astrophysics Data System (ADS)
Fillion-Gourdeau, Francois
In this dissertation, many-body physics techniques are used to study and improve ideas related to the description of heavy ion collisions at very high energy. The first part of the thesis concerns the production of tensor mesons in proton-proton (pp) collisions. An effective theory where the f2 meson couples to the energy-momentum tensor is proposed and a comparison of the inclusive cross-section computed in the collinear factorization, the k⊥-factorization and the color glass condensate is performed. A study of the phenomenology in pp collisions then shows a strong dependence on the parametrization of the unintegrated distribution function. The conclusion is that f2 meson production can be utilized to improve the understanding of the proton wave-function. In the second part, a similar investigation is performed by analysing the production cross-section of the eta' meson in pp and proton-nucleus (pA) collisions. The nucleus and proton are described by the CGC and the k⊥ -factorization respectively. A new technique for the computation of Wilson lines---color charge densities correlators in the McLerran-Venugopalan model is developped. The phenomenology shows that the cross-section in pA collisions is very sensitive to the value of the saturation scale, a crucial ingredient of the CGC picture. In the third part of the thesis, the collision term of the Boltzmann equation is derived from first principles at all orders and for any number of participating particles, starting from the full out-of-equilibrium quantum field theory and using the multiple scattering expansion. Finally, the emission of photons from a non-abelian strong classical field is investigated. A formalism based on Schwinger-Keldysh propagators relating the production rate of photons to the retarded solution of the Dirac equation in a background field is presented.
Scaling theory for anomalous semiclassical quantum transport
NASA Astrophysics Data System (ADS)
Sena-Junior, M. I.; Macêdo, A. M. S.
2016-01-01
Quantum transport through devices coupled to electron reservoirs can be described in terms of the full counting statistics (FCS) of charge transfer. Transport observables, such as conductance and shot-noise power are just cumulants of FCS and can be obtained from the sample's average density of transmission eigenvalues, which in turn can be obtained from a finite element representation of the saddle-point equation of the Keldysh (or supersymmetric) nonlinear sigma model, known as quantum circuit theory. Normal universal metallic behavior in the semiclassical regime is controlled by the presence of a Fabry-Pérot singularity in the average density of transmission eigenvalues. We present general conditions for the suppression of Fabry-Pérot modes in the semiclassical regime in a sample of arbitrary shape, a disordered conductor or a network of ballistic quantum dots, which leads to an anomalous metallic phase. Through a double-scaling limit, we derive a scaling equation for anomalous metallic transport, in the form of a nonlinear differential equation, which generalizes the ballistic-diffusive scaling equation of a normal metal. The two-parameter stationary solution of our scaling equation generalizes Dorokhov's universal single-parameter distribution of transmission eigenvalues. We provide a simple interpretation of the stationary solution using a thermodynamic analogy with a spin-glass system. As an application, we consider a system formed by a diffusive wire coupled via a barrier to normal-superconductor reservoirs. We observe anomalous reflectionless tunneling, when all perfectly transmitting channels are suppressed, which cannot be explained by the usual mechanism of disorder-induced opening of tunneling channels.
Modeling ion sensing in molecular electronics
Chen, Caroline J.; Smeu, Manuel Ratner, Mark A.
2014-02-07
We examine the ability of molecules to sense ions by measuring the change in molecular conductance in the presence of such charged species. The detection of protons (H{sup +}), alkali metal cations (M{sup +}), calcium ions (Ca{sup 2+}), and hydronium ions (H{sub 3}O{sup +}) is considered. Density functional theory (DFT) is used within the Keldysh non-equilibrium Green's function framework (NEGF) to model electron transport properties of quinolinedithiol (QDT, C{sub 9}H{sub 7}NS{sub 2}), bridging Al electrodes. The geometry of the transport region is relaxed with DFT. The transport properties of the device are modeled with NEGF-DFT to determine if this device can distinguish among the M{sup +} + QDT species containing monovalent cations, where M{sup +} = H{sup +}, Li{sup +}, Na{sup +}, or K{sup +}. Because of the asymmetry of QDT in between the two electrodes, both positive and negative biases are considered. The electron transmission function and conductance properties are simulated for electrode biases in the range from −0.5 V to 0.5 V at increments of 0.1 V. Scattering state analysis is used to determine the molecular orbitals that are the main contributors to the peaks in the transmission function near the Fermi level of the electrodes, and current-voltage relationships are obtained. The results show that QDT can be used as a proton detector by measuring transport through it and can conceivably act as a pH sensor in solutions. In addition, QDT may be able to distinguish among different monovalent species. This work suggests an approach to design modern molecular electronic conductance sensors with high sensitivity and specificity using well-established quantum chemistry.
Electron gas induced in SrTiO3
NASA Astrophysics Data System (ADS)
Fu, Han; Reich, K. V.; Shklovskii, B. I.
2016-03-01
This mini-review is dedicated to the 85th birthday of Prof. L.V. Keldysh, from whom we have learned so much. In this paper, we study the potential and electron density depth profiles in surface accumulation layers in crystals with a large and nonlinear dielectric response such as SrTiO3 (STO) in the cases of planar, spherical, and cylindrical geometries. The electron gas can be created by applying an induction D 0 to the STO surface. We describe the lattice dielectric response of STO using the Landau-Ginzburg free energy expansion and employ the Thomas-Fermi (TF) approximation for the electron gas. For the planar geometry, we arrive at the electron density profile n( x) ∝ ( x + d)-12/7, where d ∝ D 0 -12/7 . We extend our results to overlapping electron gases in GTO/STO/GTO heterojunctions and electron gases created by spill-out from NSTO (heavily n-type doped STO) layers into STO. Generalization of our approach to a spherical donor cluster creating a big TF atom with electrons in STO brings us to the problem of supercharged nuclei. It is known that for an atom with a nuclear charge Ze where Z > 170, electrons collapse onto the nucleus, resulting in a net charge Zn < Z. Here, instead of relativistic physics, the collapse is caused by the nonlinear dielectric response. Electrons collapse into the charged spherical donor cluster with radius R when its total charge number Z exceeds the critical value Z c ≈ R/ a, where a is the lattice constant. The net charge e Z n grows with Z until Z exceeds Z* ≈ ( R/ a)9/7. After this point, the charge number of the compact core Z n remains ≈ Z*, with the rest Z* electrons forming a sparse TF atom with it. We extend our studies of collapse to the case of long cylindrical clusters as well.
Low-Temperature Blackbodies for IR Calibrations in a Medium-Background Environment
NASA Astrophysics Data System (ADS)
Ogarev, S. A.; Samoylov, M. L.; Parfentyev, N. A.; Sapritsky, V. I.
2009-02-01
Utilization of Earth remote-sensing data to solve scientific and engineering problems within such fields as meteorology and climatology requires precise radiometric calibration of space-borne instruments. High-accuracy calibration equipment in the thermal-IR wavelength range ought to be combined during calibration procedures with the simulation of environmental conditions for space orbit (high vacuum, medium background). For more than 35 years, VNIIOFI has developed and manufactured standard radiation sources in the form of precision blackbodies (BB) functioning within wide ranges of wavelengths and working temperatures. These BBs are the spectral radiance and irradiance calibration devices in the world’s leading space research institutions, such as SDL (USA), DLR (Germany), Keldysh Space Center (Russia), RNIIKP/RISDE (Russia), NEC Toshiba Space Systems (Japan), etc. The paper contains a detailed description of low-temperature precision BBs developed at VNIIOFI. The characteristics of variable-temperature (100 K to 400 K) research-grade extended-area (up to 350 mm) BB models BB100-V1 and BB-80/350 are described (they are intended for radiometric calibrations by comparison with a primary standard source), as well as those that can be used as sources for high-accuracy IR calibration of space-borne and other systems not requiring a vacuum environment. The temperature nonuniformity and stability of these BBs are (0.05 to 0.1) K (cavity-type BB100-V1), and 0.1 % for the (1.5 to 15) μm wavelength region under cryo-vacuum conditions of a medium-background environment.
Evidence for broken Galilean invariance at the quantum spin Hall edge
NASA Astrophysics Data System (ADS)
Geissler, Florian; Crépin, François; Trauzettel, Björn
2015-12-01
We study transport properties of the helical edge channels of a quantum spin Hall insulator, in the presence of electron-electron interactions and weak, local Rashba spin-orbit coupling. The combination of the two allows for inelastic backscattering that does not break time-reversal symmetry, resulting in interaction-dependent power-law corrections to the conductance. Here, we use a nonequilibrium Keldysh formalism to describe the situation of a long, one-dimensional edge channel coupled to external reservoirs, where the applied bias is the leading energy scale. By calculating explicitly the corrections to the conductance up to fourth order of the impurity strength, we analyze correlated single- and two-particle backscattering processes on a microscopic level. Interestingly, we show that the modeling of the leads together with the breaking of Galilean invariance has important effects on the transport properties. Such breaking occurs because the Galilean invariance of the bulk spectrum transforms into an emergent Lorentz invariance of the edge spectrum. With this broken Galilean invariance at the quantum spin Hall edge, we find a contribution to single-particle backscattering with a very low power scaling, while in the presence of Galilean invariance the leading contribution will be due to correlated two-particle backscattering only. This difference is further reflected in the different values of the Fano factor of the shot noise, an experimentally observable quantity. The described behavior is specific to the Rashba scatterer and does not occur in the case of backscattering off a time-reversal-breaking, magnetic impurity.
Quantum Transport Modeling of Atomic Nanostructures on Silicon
NASA Astrophysics Data System (ADS)
Smeu, Manuel
Surface effects can adversely influence the performance of a nanoelectronic device, but may also lead to new functionality. The focus of this thesis is to theoretically study the role of surfaces in nanoelectronics. Our theoretical analysis is from atomic first principles achieved by combining density functional theory with the Keldysh nonequilibrium Green's function approach. This technique allows for all atoms in a system to be treated on an equal footing without any phenomenological parameters. The first part of the thesis considers conduction through a molecule with no substrate to illustrate the sort of system typically modeled in transport calculations. Two Au electrodes are bridged by a substituted benzenediamine molecule (R = CH3, NH2, OH) where an H atom is removed to form a radical that may behave as a spin filter, depending on the R group. Next is considered a π-stacked line of ethylbenzene molecules on the Si(100) surface, where the Si atoms are explicitly included in the calculation. Although the molecules conduct electrons at certain energies, a channel occurs through the substrate, which can dominate the conductance. The use of substituent groups to modulate the electron transport properties of such wires is also investigated, showing that the conductance of the molecular wire could be tuned to dominate over the substrate. Finally, the conductance of the Si(111)-7 × 7 metallic surface is studied. Inspired by experiments suggesting that atomic steps reduce the surface conductance, the atomic structure and transport properties of such steps are examined, revealing that dimer atom buckling along the step edges is the primary culprit since it leads to an opening of a local band gap at the step.
Ma, Minjie; Jalil, Mansoor Bin Abdul; Tan, Seng Gee
2013-03-15
The spin-dependent transport through a diluted magnetic semiconductor quantum dot (QD) which is coupled via magnetic tunnel junctions to two ferromagnetic leads is studied theoretically. A noncollinear system is considered, where the QD is magnetized at an arbitrary angle with respect to the leads' magnetization. The tunneling current is calculated in the coherent regime via the Keldysh nonequilibrium Green's function (NEGF) formalism, incorporating the electron-electron interaction in the QD. We provide the first analytical solution for the Green's function of the noncollinear DMS quantum dot system, solved via the equation of motion method under Hartree-Fock approximation. The transport characteristics (charge and spin currents, and tunnel magnetoresistance (TMR)) are evaluated for different voltage regimes. The interplay between spin-dependent tunneling and single-charge effects results in three distinct voltage regimes in the spin and charge current characteristics. The voltage range in which the QD is singly occupied corresponds to the maximum spin current and greatest sensitivity of the spin current to the QD magnetization orientation. The QD device also shows transport features suitable for sensor applications, i.e., a large charge current coupled with a high TMR ratio. - Highlights: Black-Right-Pointing-Pointer The spin polarized transport through a diluted magnetic quantum dot is studied. Black-Right-Pointing-Pointer The model is based on the Green's function and the equation of motion method. Black-Right-Pointing-Pointer The charge and spin currents and tunnel magnetoresistance (TMR) are investigated. Black-Right-Pointing-Pointer The system is suitable for current-induced spin-transfer torque application. Black-Right-Pointing-Pointer A large tunneling current and a high TMR are possible for sensor application.
Noise due to field- and current instabilities in CdS
NASA Astrophysics Data System (ADS)
Böer, Karl W.
1999-04-01
In this review paper, we summerize the field and current instabilities that occur when the conductivity decreases more than linearly with increasing field, or increases sufficient steeply with increased current density. In both cases well defined transition ranges exist that causes a chaotic development of field-or current-inhomogeneities, respectively. These are the ranges in which substantial additional low-frequency electronic noise is generated that shows a typical 1/f behavior. Field instabilities occur in a range of an N-shaped current-voltage characteristic that result in high-field domains which can be stationary or move through the device and cause a stationary or oscillating reduction in current. The latter, as the Gunn effect, enjoys technical application as an ac generator. In CdS the negative differential conductivity regime is trap-controlled and thereby kinetic effects are slowed down so that they can be observed visually, using the Franz-Keldysh effect. During such observation, chaotic effects can be seen before the periodic oscillations are organized, and cause a substantial increase in low-frequency noise. The chaotic initiation of well organized periodically moving high-field domains are discussed in a phase-portrait analysis of the nonlinear dynamics for pattern formation in semiconductor devices. Also in an S-shaped characteristic that is initiated by substantial Joule's heating and yields current channel formation, current instabilities can occur that lead to low frequency noise. The related phenomena are briefly summerized in this review. The experimental evidence of these chaotic developments of field- and current-instabilities is shown during the oral presentation in a movie, using electro-optical or electro-thermo-optical effects for visualization.
Electron-positron pair production from vacuum in the field of high-intensity laser radiation
NASA Astrophysics Data System (ADS)
Popov, V. S.; Mur, V. D.; Narozhnyi, N. B.; Popruzhenko, S. V.
2016-03-01
The works dealing with the theory of e + e - pair production from vacuum under the action of highintensity laser radiation are reviewed. The following problems are discussed: pair production in a constant electric field E and time-variable homogeneous field E( t); the dependence of the number of produced pairs {N_{{e^ + }{e^ - }}} on the shape of a laser pulse (dynamic Schwinger effect); and a realistic three-dimensional model of a focused laser pulse, which is based on exact solution of Maxwell's equations and contains parameters such as focal spot radius R, diffraction length L, focusing parameter Δ, pulse duration τ, and pulse shape. This model is used to calculate {N_{{e^ + }{e^ - }}} for both a single laser pulse ( n = 1) and several ( n ≥ 2) coherent pulses with a fixed total energy that simultaneously "collide" in a laser focus. It is shown that, at n ≫ 1, the number of pairs increases by several orders of magnitude as compared to the case of a single pulse. The screening of a laser field by the vapors that are generated in vacuum, its "depletion," and the limiting fields to be achieved in laser experiments are considered. The relation between pair production, the problem of a quantum frequency-variable oscillator, and the theory of groups SU(1, 1) and SU(2) is discussed. The relativistic version of the imaginary time method is used in calculations. In terms of this version, a relativistic theory of tunneling is developed and the Keldysh theory is generalized to the case of ionization of relativistic bound systems, namely, atoms and ions. The ionization rate of a hydrogen-like ion with a charge 1 ≤ Z ≤ 92 is calculated as a function of laser radiation intensity ( F and ellipticity ρ.
Quantum biology: Elucidating design principles from photosynthesis
NASA Astrophysics Data System (ADS)
Pelzer, Kenley March Barrett
Light-harvesting complexes in photosynthetic organisms are known to transfer excitonic energy with extremely high efficiency, but the mechanisms behind this high efficiency are not fully understood. Spectroscopic data on the Fenna-Matthews-Olson (FMO) complex, a light-harvesting complex in green sulfur bacteria, suggests that quantum mechanical effects may play an important role in the energy transfer process. In recent years a large body of research has supported the argument that quantum mechanical effects can and do play a role in photosynthetic energy transfer, but both experimental and theoretical work faces the challenge of understanding the role of FMO's noisy biological environment in quantum transport. It is certain that excitons in FMO are frequently perturbed by phonons in the environment, but much remains to be understood about the role of these perturbations in the transport process. This thesis aims to contribute to this discussion in two ways. First, we present work in which we apply theoretical models to address questions regarding the interpretation of spectroscopic results. The accuracy of spectroscopy in measuring timescales relevant to quantum transport and the relevance of spectroscopic results to excitation by incoherent light are addressed. Second, we present work in which we simulate exciton transport using various representations of the phonon bath. We explore the effect of spatial correlations in the phonon bath, and test a variety of possible bath models in a Keldysh Green's function model of transport under incoherent light. We demonstrate in many ways that environmental noise plays a crucial role in shaping the process of excitonic energy transfer.
Oceanic Precipitation Measurement - Surface Validation
NASA Astrophysics Data System (ADS)
Klepp, Christian
2013-04-01
State-of-the-art satellite derived and reanalysis based precipitation climatologies still show remarkably large differences in frequency, amount, intensity, variability and temporal behavior of precipitation over the oceans. Additionally so far appropriate in-situ validation instruments were not available for shipboard use. The uncertainties are largest for light precipitation within the ITCZ and subtropics and for cold season high-latitude precipitation including mix-phase and snowfall. Hence, a long-term issue on which IPWG and GPM-GV is urging more attention is the provision of high quality surface validation data in oceanic areas using innovative ship-based instruments. Precipitation studies would greatly benefit from systematic dataset collection and analysis as such data could also be used to constrain precipitation retrievals. To achieve this goal, the KlimaCampus and Max Planck Institute for Meteorology in Hamburg, Germany funded this project that uses automated shipboard optical disdrometers, called Eigenbrodt ODM470, that are capable of measuring liquid and solid precipitation using drop size distributions in minute intervals on moving ships with high accuracy even under high wind speeds and rough sea states. Since the project start in 2009 the statistical basis for a conclusive validation has significantly improved with comprehensive data collection of more than 3 million minutes of precipitation measurements onboard six ships. Currently, six ODM470 instrument systems are available of which three are long-term mounted onboard the German research icebreaker R/V Polarstern (Alfred Wegner Institut) since June 2010, on R/V Akademik Ioffe (P.P.Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia) since September 2010 and on R/V Maria S. Merian (Brise Research, University of Hamburg) since December 2011. Three instruments are used for additional short-term shipboard campaigns and intercomparison projects. The core regions for these
Morphology of the Knipovich Ridge Area
NASA Astrophysics Data System (ADS)
Zarayskaya, Y.; Abramova, A.; Dobrolyubova, K.; Mazarovich, A.; Moroz, E.
2014-12-01
Knipovich Ridge is the northernmost part of the Mid-Atlantic Ridge system. It is located between Mohns and Molloy spreading centers in the Greenland Sea. The scientific team of the R/V "Akademik Nikolaj Strakhov" (Geological Institute RAS, Russia) surveyed this area in 2006, 2007, 2009 and 2010 using the deep-water multibeam echosounder RESON Seabat 7150 with working frequency 12 kHz. The total surveyed area is up to 82000 km² including 65000 km² covering rift valley and flanges of the ridge. Knipovich ridge is classified as an ultra-slow oblique spreading center with spreading rate around 1,4 cm/y. Its large-scale morphological features are reduced in number comparing to other mid-ocean ridges. Eastern flange is buried under the continental slope sediments and only the rare highest peaks rise above this cover. Western flange is fully developed and consists of several ridges prolonged parallel to the rift valley. Ridges are supplemented with individual highs. Rift valley is 20-40 km wide and 500 km long. Its depth is 3300-3700 m. Valley slopes have terraces and ledges of different amplitudes. The bottom of the valley is echeloned by 5 volcanic axial highs rising 400 - 1000 m above it. Spreading obliquity is imprinted in the ridge morphology. The global models predict a plate motion vector of 307º. The main ridge axis has general orientation of 350º. Rift valley follows this direction from the South, and on the half way to the North turns to azimuth of 2º. The detailed bathymetry shows that small-scale features orientation differs. Rift axial highs and individual flange highs are prolonged NW-SE under azimuth of 30º. This orientation is sub-perpendicular to the plate motion vector (83º) and oblique to the ridge axes (40º). The multibeam bathymetry shows no sing of transform faults or non-transform discontinuities along the Knipovich ridge rift valley. There is one strong lineation in the northern part of the ridge. It includes flange and axial highs and
NASA Astrophysics Data System (ADS)
Fokina, A.; Akhmanov, G.; Andreassen, K.
2013-12-01
Bottom sampling in several areas of the Barents Sea and sub-sampling of gases from collected sediments were carried out as part of various geological marine expeditions. These expeditions were organized by the UNESCO-MSU Training and Research Centre for Marine Geology and Geophysics of the Moscow State University (Russia) and the University of Tromso (Norway) onboard R/V "Akademik Nikolaj Strakhov" and R/V 'Helmer Hanssen' during the period of 2011-2013. A total of 304 gas samples from 51 different stations were analyzed using Gas Chromatography (GC) and Isotope Ratio Mass-Spectrometry (IRMS) techniques. These were combined in a database which was used to investigate the relationship between the type of depositional environment, hydrocarbon gas concentration and sediment composition. Gas samples, collected from shelf deposits, mainly consist of methane (90-99%) with little admixture of ethane and propane. Unsaturated homologues were detected in all samples. Ethylene and propylene predominate over saturated homologues. This, together with the isotopic composition, suggests a biogenic nature of the gases collected in most areas. Gas concentrations were found to be very low for the majority of analyzed sediment samples. This is indicative for their low filtration capacity and low organic matter content. The cause of this is believed to be the pelitic clayey composition of the sediments, their high compaction and the generally frugal bioproductivity in arctic regions. A specific molecular and isotopic composition and high concentrations of gas are characteristic for the zones of focused hydrocarbon seepage on the seafloor that were studied during the cruises. Areas with pockmarks, outcropping salt diapirs and gas flares above the seafloor were classified high petroleum potentials, such as the Hjalmar Johansen High and the North-Kildenskoe gas field, was examined in order to verify characteristics of gas emission from deeply seated accumulations of natural hydrocarbon
The Dissipation Rate In The Wind-induced Ekman Boundary Layer
NASA Astrophysics Data System (ADS)
Roget, E.; Figueroa, M.; Lozovatsky, I.
Turbulent measurements in the near-surface oceanic boundary layer carried out at the trans-Atlantic section (along 53N) in 2001 are used to study variations of the intensity of ocean mixing influenced by various atmospheric forcing including stormy winds. Measurements were taken from the Russian r/v Akademik Ioffe (IO RAN) during its 9th research cruise. Atmospheric data were obtained in the course of regular standard meteorological observations. Microstructure oceanographic measurements were made from the sea surface down to the depth of about 200 m using a profiler developed by SeaSun Technology GmbH (Germany). The profiler was equipped by an airfoil sensor to measure small-scale shear with further calculation of the kinetic energy dissipation rate, fast and slow temperature sensors, a conductivity probe, and a pressure sensor. To control level of vibrations during downcasts, acceleration signal was recorded and fur- ther analyzed with respect to the airfoil record. The data were transmitted onboard via a thin cable of almost neutral buoyancy that was realized with a slightly higher speed than the falling speed of the profiler to reduce possible vibrations caused by cable ten- sion. Upper 5-10 meters of the measurements were eliminated from the analysis due to the ship-induced contaminations. The background hydrological information was ob- tained by a ship-mounted ADCP and a Neil Brown profiler. The ADCP measurements showed that wind-induced drift currents usually occupy the upper 30-40 meter layer under moderate winds (Va < 10 m/s). The decimal logarithm of dissipation rate in this layer varies from -6 to -8 W/kg depending on the age of the wind-induced turbulence. When the measurements were made after an intense storm (Va > 25 m/s), the depth of the Ekman layer increased to about 80 m keeping high dissipation (log10eps > -6 W/kg) across the whole layer. The dissipation at the higher depths, in the thermohalo- cline, usually had an intermittent nature with a
NASA Astrophysics Data System (ADS)
Fokina, A.; Akhmanov, G.; Andreassen, K.; Yurchenko, A.
2014-12-01
In 2011-2013 four research cruises in the Barents Sea were organized by UNESCO-MSU Centre for Marine Geology and Geophysics (Russia) and University of Tromso (Norway) and were carried out onboard the RV "Akademik N. Strakhov" and RV "Helmer Hanssen". The cruises were devoted to finding and studying hydrocarbon seeps (e.g. pockmarks, crater-like structures), evaluating neo-tectonic activity and focusing on some problems in the field of modern geological and geochemical processes in the Arctic region. This topic is focused on identification of the gas anomalies related to the possible cold seep structures, study of the molecular and isotopic composition and origin of the hydrocarbon gases from the bottom sediments. During this research the interpretation of geochemical survey data was carried out within the different structures of the Barents region: 1) The area of distribution of craters, 2) Storfjordrenna and Storfiordbanken, 3) Nordkap and Tiddly basins, Fedynskii high, North-Kildinsk field. 1) In the Central Barents Sea in the area of distribution of craters residual discharge of gas from the Triassic sandstones has occurred and manifested through the activity of gas flares and elevated concentrations of methane. Values of gas coefficients indicate the possible existence of thermogenic gas in the sample. The active unloading of gas and formation of craters associated with the disintegration of gas hydrates. 2) Discovered gas flares, pockmarks and abnormal high concentrations of methane are the first statement about the presence of active gas discharge in the NW Barents Sea. HC gases are formed as a result of microbial processing of thermogenic gas. In the area there is an increased microbial activity resulting in authigenic carbonate formation. Unloading of gas is observed in the edges parts of the large glacial moraine along the base of which the lateral migration of gas occurs. Reservoirs can be Lower-Middle and Lower-Middle Triassic sandstones. 3) In the
NASA Astrophysics Data System (ADS)
Gritsenko, Alexander; Tarakanov, Roman
2016-04-01
Fine jet structure of the Antarctic Circumpolar Current (ACC) in the Drake Passage is investigated on the basis of the daily satellite data of the absolute dynamic topography (ADT) provided by the French CLS Agency (DT-Global-MADT-Upd product, http://aviso.oceanobs.com) and sea surface temperature (SST) provided by the GAMSSA Project (Global Australian Multi-Sensor SST Analysis, http://data.nodc.noaa.gov/las/getUI.do?dsid=id-c80878d11f&varid=analysed_sst-id-c80878d11f&auto=true) of the Centre for Australian Weather and Climate Research. The investigation was executed on 01.09.2011-31.12.2011 using the methods of the probability-statistical analysis. Mesoscale eddies were eliminated from the analysis of fine jet structure of the ACC in the Drake Passage. As a result the amplitude of the ADT and SST gradients increased. This allowed us to distinguish more precisely the limits and cores of the jets. The jet limits were chosen as the isopleths of the ADT (isohypses) matching with the local minima of the ADT and SST gradients (averaged in time) along ADT axis in ADT-gradient-ADT and SST-gradient-ADT spaces, while the cores of the jets coincided with the local maxima of the SST and ADT gradients at the corresponding isohypses. The main feature of the studied region is merging of the separated jets into a powerful "superjet" as the ACC passes through the passage. It is possible to separate and identify these separated jets if we have auxiliary (e.g. sub-satellite) information. With this in mind we used the CTD- and SADCP-measurements over the section carried out on 28.10.2011-04.11.2011 onboard R/V "Akademik Ioffe" across the Drake Passage. The analyses of the satellite data revealed 8-9 individual jets characterized by the local horizontal maxima of the ADT and SST gradients. These jets were actually various combinations of the twelve ACC jets, which we found earlier south of Africa. In September-October 2011, we found 6 jets of the Subantarctic Current, 4 jets of the
NASA Astrophysics Data System (ADS)
Lembke-Jene, L.; Biebow, N.; Wolff-Boenisch, B.; Thiede, J.; European Research Icebreaker Consortium
2011-12-01
Research vessels dedicated to work in polar ice-covered waters have only rarely been built. Their history began with Fritjof Nansen's FRAM, which he used for his famous first crossing of the Arctic Ocean 1893-1896. She served as example for the first generation of polar research vessels, at their time being modern instruments planned with foresight. Ice breaker technology has developed substantially since then. However, it took almost 80 years until this technical advance also reached polar research, when the Russian AKADEMIK FEDEROV, the German POLARSTERN, the Swedish ODEN and the USCG Cutter HEALY were built. All of these house modern laboratories, are ice-breakers capable to move into the deep-Arctic during the summer time and represent the second generation of dedicated polar research vessels. Still, the increasing demand in polar marine research capacities by societies that call for action to better understand climate change, especially in the high latitudes is not matched by adequate facilities and resources. Today, no icebreaker platform exists that is permanently available to the international science community for year-round expeditions into the central Arctic Ocean or heavily ice-infested waters of the polar Southern Ocean around Antarctica. The AURORA BOREALIS concept plans for a heavy research icebreaker, which will enable polar scientists around the world to launch international research expeditions into the central Arctic Ocean and the Antarctic continental shelf seas autonomously during all seasons of the year. The European Research Icebreaker Consortium - AURORA BOREALIS (ERICON-AB) was established in 2008 to plan the scientific, governance, financial, and legal frameworks needed for the construction and operation of this first multi-nationally owned and operated research icebreaker and polar scientific drilling platform. By collaborating together and sharing common infrastructures it is envisioned that European nations make a major contribution to
NASA Astrophysics Data System (ADS)
Ivanova, E. V.; Borisov, D.; Murdmaa, I.; Levchenko, O. V.; Dmitrenko, O.; Emelyanov, E.
2014-12-01
The high-resolution seismic profiling during cruise 32 of the RV "Akademik Ioffe" (2010) discovered a large elongated contourite drift on the ridge of the Rio Grande fracture zone (Brazil Basin, western South Atlantic). This sedimentary body with a thickness up to 300 m, named Ioffe drift, is traced at water depth range from 3790 to 3980 m. Five seismic units are distinguished within the upper drift structure recorded to a depth of 60 mbsf. The seismic units are separated by angular discontinuities. The sediment core AI-2436 (25°51.6'S, 34°01.40'W, water depth 3800 m) retrieved near the drift top recovers about 6 m of nanno-foraminiferal ooze intercalated with foraminiferal sand interbeds. According to the planktonic foraminiferal and nannofossil stratigraphy, the sediment record embraces about 3 My of the Ioffe drift history, from the Late Pliocene to present. Absence of several foraminiferal and nannofossil zones in the core section indicates long-term hiatuses. Some zones are thicker here while others are reduced as compared to those on the nearby Rio Grande Rise. This suggests reworking of the biogenic material in the drift. The Ioffe drift was formed as a result of transport and deposition of biogenic calcareous material by the eastern branch of the Antarctic bottom water (AABW) flow. The biogenic calcareous material is mainly derived from the Rio Grande Rise where planktonic foraminiferal and nannofossil assemblages identical to those in core AI-2436 are studied at the DSDP site 516 (Barash et al., 1983). We suggest that the grain-size distribution of the calcareous sediments roughly corresponding to the foraminiferal/nannofossil ratio reflects the bottom currents velocity variations. Very high current velocities result in erosion and stratigraphic hiatuses. Angular unconformities in seismic profiles indicate episodes of intensified AABW flow velocity which led to the drift migration. The study was supported by RFBR, research projects 14-05-31357-mol_a, 14
Recent Russian Geophysical and Geological Investigations on Siberian Continental Margin
NASA Astrophysics Data System (ADS)
P. v., A.; K. v., D.; B. v., V.
2007-12-01
In July-August, 2005 new geophysical and geological data were acquired in the Mendeleev Rise (MR) region during "Arctic-2005" cruise aboard M/V "Akademik Fedorov". The study was concentrated in the southern part of MR in the area of its junction with East Siberian shelf. On-ice deep seismic sounding investigations (with offsets up to 250 km) and helicopter-supported seismic reflection soundings were performed along 600 km-long sub- longitudinal profile. Seismic survey was accompanied by on-ice gravity observations and geological sampling. Air-borne magnetic and air gravity measurements at scale 1:1,000,000 were also performed within a 100 km- wide corridor along the central seismic profile. Processing and analysis of new evidence included the compilation of deep seismic section, 2D seismic-gravity modeling of the Earth crust, 3D modeling of basement and Moho relief, and estimation of sediment and earth crust thickness. The results were integrated with earlier data and used for advanced structural and tectonic interpretations. The following main conclusions were obtained: Thickness of sediment cover along seismic line varies from 12 km in the south (in the North-Chukchi Trough) to 3-4 km in the northern MR. Crust thickness beneath MR is on the order of 30-35 km with a maximum value of 38 km in its southern part. The thinnest crust (28 km) is observed in the North-Chukchi Trough. Potential fields indicate existence of several blocks differing in gravity and magnetic anomalies. In the southern MR these blocks appear separated by grabens and display distinct continental characteristics accentuated by thickness of the crust, its seismic velocities and potential field pattern. At some of the shallowest (possibly eroded?) bathymetric highs the results of bottom sampling seem to point to the possibility of local derivation of coarse bottom debris. The proposed tectonic model implies structural continuity between MR and the adjacent East Siberian shelf. Brief information
Nitrate in situ measurements in the northern Japan Sea
NASA Astrophysics Data System (ADS)
Kaplunenko, Dmitry D.; Lobanov, Vyacheslav B.; Tishchenko, Pavel Ya.; Shvetsova, Maria G.
2013-02-01
The results of nitrate in situ measurements by the In Situ Ultraviolet Spectrophotometer (ISUS MBARI) in the northern part of the Japan Sea are reported. The observations were implemented in three cruises of R/V Akademik M.A. Lavrentyev during 2009-2010 including SoJaBio expedition. The instrument was attached to CTD/water sampling system and thus allowed to measure high resolution vertical profiles of nitrate concentration as well as profiles of water temperature, salinity, dissolved oxygen and chlorophyll-a content down to 1000 m depth. The ISUS data were calibrated using results of chemical analysis of nitrate content in water samples taken at standard depths. Comparison of discrete samples and vertical profiles showed a good correlation of R=0.93 for 240 pairs of data. On a background of general increasing of nitrate concentration with depth the ISUS profiles showed at many stations an existence of local nitrate extremes which form inversions or step-like structure of the profiles. They had a typical vertical scale from a few tens to hundred meters and were observed in various layers below seasonal pycnocline (40-50 m) and down to 1000 m. These anomalies coincide well with the anomalies in dissolved oxygen, temperature and salinity profiles and thus could be explained by mesoscale advections of low nutrient/high oxygen water associated with mixing processes in the shelf/slope area as well as at the frontal zone and mesoscale eddies. High nutrient/low oxygen intrusions were also detected at depth 40-60 m and were associated with high salinity subsurface water transported from the southern part of the sea. However, a process of organic matter remineralization just below pycnocline could be also responsible for increasing nitrate concentration there as well for the formation of local maximum or step-like structure in the subsurface layer (40-150 m) observed at many stations located close to the shelf area. Anomalies of larger vertical extent (up to 200-300 m) were
Arctic satellite thermal infrared CH4 data compared to surface in-situ and total column measurements
NASA Astrophysics Data System (ADS)
Yurganov, L.; Leifer, I.; Xiong, X.
2013-12-01
The trace gas sensitivity of Thermal InfraRed (TIR) sounders (AIRS, IASI, TANSO) is greatest in the middle and upper troposphere; though, lower troposphere (1-2 km of altitude) sensitivity is less but not negligible. As a result, where methane largely is constrained to the lower troposphere, as is common in the Arctic particularly the marine Arctic, retrievals from these instruments provides important synoptic data on high latitude methane sources. Low Arctic water vapor content favors a better sensitivity to methane as well: H2O is the main absorber in the 7.8 micrometers spectral region. Both AIRS/Aqua v6 (NASA) and IASI/Metop-A (NOAA/NESDIS/CLASS retrievals) methane data averaged over 0-4 km altitude clearly demonstrate increased methane concentrations over the Barents and Norwegian Seas (BNS) with seasonal maximum in December - March. Similar increases are observed over the Kara, Laptev, and Chukchi Seas for September-November, i.e. during the period of minimum ice cover over the Arctic (Figures 1 and 2). Comparison of a long series of AIRS data with in situ methane concentrations at the Zeppelin NILU observatory (Svalbard) show good agreement both in amplitude and phase of seasonal variations. Agreement with Barrow NOAA continuous methane in situ data is much worse, which likely results from lower thermal contrast in winter over the cold and icy surfaces of the Eastern Arctic. Further surface validation is by a comparison of total methane columns with the Sun-Tracking FTIR at Ny-Alesund, Svalbard (TCCON network). These analyses demonstrate that TIR satellites are capable of detecting Arctic methane enhancements from space, particularly over relatively warm year-round water surfaces such as the BNS. Ongoing research is addressing further verification of retrieved methane columns by collecting data with a cavity ring-down spectroscopy analyzer for methane and carbon dioxide on board of the Russian Research Vessel Akademik Fedorov during the expedition NABOS-2013
NASA Astrophysics Data System (ADS)
Skolotnev, S. G.; Bylinskaya, M. E.; Golovina, L. A.; Ipat'eva, I. S.
2011-03-01
Micropaleontological and isotope-geochronological investigations of calcareous sedimentary rocks and volcanites dredged out from the central portion of the submarine Vitoria-Trindade Ridge during the 24th cruise of R/V Akademik Vavilov have been conducted. It has been established based on micropaleontological analysis, which included determination of the species composition of foraminifera and nannoplankton, that the sequence of sedimentary rocks having a pelagic nature formed on the slopes of the volcanic seamounts in the central portion of the Vitoria-Trindade Ridge from the Early to Mid-Miocene to the Holocene; a good correlation between the degree of lithification of these rocks and their age is observed. It has also been established that the carbonate platforms on the abraded tops of the Davis Seamount and the Dogaressa Bank, which are located in the east-central portion of the Vitoria-Trindade Ridge, started forming in the Early Miocene (19-24 Ma). It has been determined using local U-Pb dating of zircon grains with a SHRIMP-II high resolution secondary ion mass spectrometer that the volcanites forming the upper portion of the volcanic rock sequence of the Jaseur Seamount (29.8 ± 6.6 Ma) located in the west-central portion of the Vitoria-Trindade Ridge date to the Oligocene. The investigations conducted have confirmed the opinion that the Vitoria-Trindade Ridge formed in general because of the activity of the hot spot located under the volcanic Trindade and Martin Vaz Islands. However, separate extended lenticular segments of this ridge existed for a long time as single structures, within which the age of the seamounts was not linearly dependent on the distance from the location of the hot spot. Lenses of hot mantle matter that form at the sublithospheric level as a result of impulses of plume activity and move along with the lithospheric plate play a defining role in the development of individual segments forming the Vitoria-Trindade Ridge.
NASA Astrophysics Data System (ADS)
Duliu, O. G.; Alexe, V. E.; Moutte, J.; Szobotca, S. A.
2009-04-01
The concentrations of seven major components (Ti, Fe, Mg, Ca, Na, K and P as oxides) and 15 trace elements (Sc, V, Cr, Ni, Cu, Sr, Y, Zr, Ba, La, Ce, Nd, Eu, Yb and Th) were determined by ICP-AE spectrometry in 27 samples of manganese nodules, micronodules and abyssal clay collected by dredging during the 1984 cruise of the R/V Akademik Alexandr Karpinski in the Clarion-Clipperton Province of the North Pacific (12° N-12° 40' N and 137° 40' W-138° 50' W) at a depth of about 4,500 m. Cluster analysis was used to compare among individual as well as pooled datasets, in addition to different indicators such as La/Th, Ni/Cu and LREE/HREE ratios for the Clarion-Clipperton samples, as well as between these and corresponding values for the upper continental crust (UCC), North America Shale Composite (NASC), and igneous Indian and Pacific Mid-Ocean Ridge Basalts (MORBs). The results evidenced the existence of significant positive correlations between major components in the Clarion-Clipperton samples and Pacific Ocean MORB, whereas trace elements (excepting Ni and Cu) correlate better with the UCC and NASC. There was also evidenced a depletion in LREEs which, together with a Ce negative anomaly for all Clarion-Clipperton samples, pointed towards a hydrothermal origin of the all REE, this fact being sustained by a La/Th ratio between 5 and 7, different from UCC (2.80) and NASC (2.50), but closer to Pacific (8.8) and Indian (11.25) Oceans MORBs. On the other hand, on a Sc-La-Th ternary diagram, all Clarion-Clipperton samples grouped together closer UCC and NASC and far away from both Pacific and Indian Oceans MORBs. At the same time, all investigated samples showed more significant clusters such as phosphorous pentoxide and all REE excepting Ce, or Ni and Cu. Compared to abyssal clay, the nodule as well as micronodules show significant enrichment in Ni and Cu while a constant Ni/Cu ratio indicated that all samples come from the sediment surface. In this way, the
Ecological state of North -Western Black Sea macrobenthos on offshore bottoms deeper than 50 m
NASA Astrophysics Data System (ADS)
Gomoiu, M.-T.; Begun, T.; Teaca, A.
2009-04-01
In the last 10-15 years researches concerning benthos in the north-western Black Sea were focused mainly on inshore bottoms, usually less than 50 m deep, where important ecological changed occurred. The offshore bottoms, deeper than 50 m, and especially the periazoic level at the edge of the continental shelf have been less known, the information being scarce. The present study gathers the results of the researches carried out in the past 12 years on the Modiolus phaseolinus community, including the periazoic level, and allows a comparison to be drawn with the situation of the so-called "ecological stability" period at the beginning of the 1960s, before the ecosystemic disturbances began in the Black Sea. In 1995-2007, a number of 133 quantitative macro-benthos samples were collected at depths of 50 - 213 m by means of the van Veen-type grab and box corer; these samples were taken during several cruises (R/V "Prof.Vodyanitskyi" EROS 1995, 1997, R/V „Akademik" 2003, R/V „Parshin" 2005, R/V „Akademik" 2006 R/V „Mare Nigrum" 2006 and 2007), the researches aiming at the assessment of the benthic ecosystem state. The analyses of the 133 samples helped identify 191 taxa (Vermes - 88, Mollusca - 24, Crustacea - 32 and Varia - 47), approximately 60% of the total number of species recorded in the north-western Black Sea during the period of "ecological prosperity". The mean abundance of the benthic populations was 4,836.2 indvs.m-2 for density and 189.9 g.m-2 for biomass. Most macrobenthic taxa occurred in the samples accidentally; out of the 191 taxa recorded, 60 taxa had a frequency of 1-2%, 37 taxa 2-5%, 28 taxa 5-10%, 32 taxa 10-20%, 26 taxa 20-50% and only eight species had a frequency over 50% (Modiolus phaseolinus, Terebelides stroemi, Capitella capitata, Nephtys hombergi, Amphiura stepanovi, Sphaerosyllis bulbosa, Apseudes ostroumovi and Phyllodoce lineata). Numerical abundances were dominated by worms (2,606.9 indvs.m-2) and molluscs (1,398.7 indvs.m-2
Efficient Sub-Bandgap Light Absorption and Signal Amplification in Silicon Photodetectors
NASA Astrophysics Data System (ADS)
Liu, Yu-Hsin
This thesis focuses on two areas in silicon photodetectors, the first being enhancing the sub-bandgap light absorption of IR wavelenghts in silicon, and the second being intrinsic signal amplification in silicon photodetectors. Both of these are achieved using heavily doped p-n junction devices which create localized states that relax the k-selection rule of indirect bandgap material. The probability of transitions between impurity band and the conduction/valence band would be much more efficient than the one between band-to-band transition. The waveguide-coupled epitaxial p-n photodetector was demonstrated for 1310 nm wavelength detection. Incorporated with the Franz-Keldysh effect and the quasi-confined epitaxial layer design, an absorption coefficient around 10 cm-1 has been measured and internal quantum efficiency nearly 100% at -2.5V. The absorption coefficient is calculated from the wave function of the electron and hole in p-n diode. The heavily doped impurity wave function can be formulated as a delta function, and the quasi-confined conduction band energy states, and the wave function on each level can be obtained from the Silvaco software. The calculated theoretical absorption coefficient increases with the increasing applied bias and the doping concentration, which matches the experimental results. To solve the issues of large excess noise and high operation bias for avalanche photodiodes based on impact ionization, I presented a detector using the Cycling Excitation Process (CEP) for signal amplification. This can be realized in a heavily doped and highly compensated Si p-n junction, showing ultra high gain about 3000 at very low bias (<4 V), and possessing an intrinsic, phonon-mediated regulation process to keep the device stable without any quenching device required in today's Geiger-mode avalanche detectors. The CEP can be formulated with the rate equations in conduction bands and impurity states. The gain expression, which is a function of the
SymGF: A Symbolic Tool for Quantum Transport Theory
NASA Astrophysics Data System (ADS)
Feng, Zi Min
In this thesis, I report the development and application of a symbolic derivation tool named "SymGF'' - standing for Symbolic Green's Function, that can automatically and analytically derive quantum transport expressions and the associated Keldysh nonequilibrium Green's functions (NEGF). Quantum transport happens in open systems consisting of a scattering region coupled to external electrodes. When there are strong electron-electron interactions in the scattering region, analytical derivations of the Green's functions can be very tedious and error prone. Running on a personal computer, SymGF derives the necessary analytical formulas at a level of correlation specified by the user, using the equation of motion (EOM) method. The input to SymGF are the second quantized form the device Hamiltonian, the (anti)commutators of the operators that appear in the Hamiltonian, and a truncation rule for the correlators which determines the accuracy of the final outcome. The output of SymGF are the analytical expressions of transport properties such as electric current and conductance in terms of various Green's functions; as well as the Green's functions themselves in terms of the unperturbed non-interacting Green's functions that can be obtained straightforwardly. For systems where electron-electron interaction can be neglected, the transport problems can be easily solved and SymGF is not necessary - even though SymGF gives the same answer; but for interacting systems SymGF drastically reduces the mathematical burden of analytical derivations. We have tested SymGF for several transport problems involving Kondo resonances where analytical derivations were done by humans: exactly the same results were obtained by SymGF but in a tiny fraction of time. We have applied SymGF to new and very hard problems that resist analytical derivations by hand, including quantum transport in a double quantum dot system; transport through a single quantum dot in parallel to a direct lead
Strong-field and attosecond physics in solids
Ghimire, Shambhu; Ndabashimiye, Georges; DiChiara, Anthony D.; Sistrunk, Emily; Stockman, Mark I.; Agostini, Pierre; DiMauro, Louis F.; Reis, David A.
2014-10-08
We review the status of strong-field and attosecond processes in bulk transparent solids near the Keldysh tunneling limit. For high enough fields and low-frequency excitations, the optical and electronic properties of dielectrics can be transiently and reversibly modified within the applied pulse. In Ghimire et al (2011 Phys. Rev. Lett. 107 167407) non-parabolic band effects were seen in photon-assisted tunneling experiments in ZnO crystals in a strong mid-infrared field. Using the same ZnO crystals, Ghimire et al (2011 Nat. Phys. 7 138–41) reported the first observation of non-pertubative high harmonics, extending well above the bandgap into the vacuum ultraviolet. Recent experiments by Schubert et al (2014 Nat. Photonics 8 119–23) showed a carrier envelope phase dependence in the harmonic spectrum in strong-field 30 THz driven GaSe crystals which is the most direct evidence yet of the role of sub-cycle electron dynamics in solid-state harmonic generation. The harmonic generation mechanism is different from the gas phase owing to the high density and periodicity of the crystal. For example, this results in a linear dependence of the high-energy cutoff with the applied field in contrast to the quadratic dependence in the gas phase. Sub-100 attosecond pulses could become possible if the harmonic spectrum can be extended into the extreme ultraviolet (XUV). Here we report harmonics generated in bulk MgO crystals, extending tomore » $$\\sim 26$$ eV when driven by ~35 fs, 800 nm pulses focused to a ~1 VÅ$$^{-1}$$ peak field. The fundamental strong-field and attosecond response also leads to Wannier–Stark localization and reversible semimetallization as seen in the sub-optical cycle behavior of XUV absorption and photocurrent experiments on fused silica by Schiffrin et al (2013 Nature 493 70–4) and Schultze et al (2013 Nature 493 75–8). These studies are advancing our understanding of fundamental strong-field and attosecond physics in solids with potential
Control of noisy quantum systems: Field-theory approach to error mitigation
NASA Astrophysics Data System (ADS)
Hipolito, Rafael; Goldbart, Paul M.
2016-04-01
We consider the basic quantum-control task of obtaining a target unitary operation (i.e., a quantum gate) via control fields that couple to the quantum system and are chosen to best mitigate errors resulting from time-dependent noise, which frustrate this task. We allow for two sources of noise: fluctuations in the control fields and fluctuations arising from the environment. We address the issue of control-error mitigation by means of a formulation rooted in the Martin-Siggia-Rose (MSR) approach to noisy, classical statistical-mechanical systems. To do this, we express the noisy control problem in terms of a path integral, and integrate out the noise to arrive at an effective, noise-free description. We characterize the degree of success in error mitigation via a fidelity metric, which characterizes the proximity of the sought-after evolution to ones that are achievable in the presence of noise. Error mitigation is then best accomplished by applying the optimal control fields, i.e., those that maximize the fidelity subject to any constraints obeyed by the control fields. To make connection with MSR, we reformulate the fidelity in terms of a Schwinger-Keldysh (SK) path integral, with the added twist that the "forward" and "backward" branches of the time contour are inequivalent with respect to the noise. The present approach naturally and readily allows the incorporation of constraints on the control fields—a useful feature in practice, given that constraints feature in all real experiments. In addition to addressing the noise average of the fidelity, we consider its full probability distribution. The information content present in this distribution allows one to address more complex questions regarding error mitigation, including, in principle, questions of extreme value statistics, i.e., the likelihood and impact of rare instances of the fidelity and how to harness or cope with their influence. We illustrate this MSR-SK reformulation by considering a model
Recent progress of probing correlated electron states by point contact spectroscopy.
Lee, Wei-Cheng; Greene, Laura H
2016-09-01
We review recent progress in point contact spectroscopy (PCS) to extract spectroscopic information out of correlated electron materials, with the emphasis on non-superconducting states. PCS has been used to detect bosonic excitations in normal metals, where signatures (e.g. phonons) are usually less than 1% of the measured conductance. In the superconducting state, point contact Andreev reflection (PCAR) has been widely used to study properties of the superconducting gap in various superconductors. It has been well-recognized that the corresponding conductance can be accurately fitted by the Blonder-Tinkham-Klapwijk (BTK) theory in which the AR occurring near the point contact junction is modeled by three parameters; the superconducting gap, the quasiparticle scattering rate, and a dimensionless parameter, Z, describing the strength of the potential barrier at the junction. AR can be as large as 100% of the background conductance, and only arises in the case of superconductors. In the last decade, there have been more and more experimental results suggesting that the point contact conductance could reveal new features associated with the unusual single electron dynamics in non-superconducting states, shedding a new light on exploring the nature of the competing phases in correlated materials. To correctly interpret these new features, it is crucial to re-examine the modeling of the point contact junctions, the formalism used to describe the single electron dynamics particularly in point contact spectroscopy, and the physical quantity that should be computed to understand the conductance. We will summarize the theories for point contact spectroscopy developed from different approaches and highlight these conceptual differences distinguishing point contact spectroscopy from tunneling-based probes. Moreover, we will show how the Schwinger-Kadanoff-Baym-Keldysh (SKBK) formalism together with the appropriate modeling of the nano-scale point contacts randomly distributed
NASA Astrophysics Data System (ADS)
Nagaosa, Naoto; Sinova, Jairo; Onoda, Shigeki; MacDonald, A. H.; Ong, N. P.
2010-04-01
The anomalous Hall effect (AHE) occurs in solids with broken time-reversal symmetry, typically in a ferromagnetic phase, as a consequence of spin-orbit coupling. Experimental and theoretical studies of the AHE are reviewed, focusing on recent developments that have provided a more complete framework for understanding this subtle phenomenon and have, in many instances, replaced controversy by clarity. Synergy between experimental and theoretical works, both playing a crucial role, has been at the heart of these advances. On the theoretical front, the adoption of the Berry-phase concepts has established a link between the AHE and the topological nature of the Hall currents. On the experimental front, new experimental studies of the AHE in transition metals, transition-metal oxides, spinels, pyrochlores, and metallic dilute magnetic semiconductors have established systematic trends. These two developments, in concert with first-principles electronic structure calculations, strongly favor the dominance of an intrinsic Berry-phase-related AHE mechanism in metallic ferromagnets with moderate conductivity. The intrinsic AHE can be expressed in terms of the Berry-phase curvatures and it is therefore an intrinsic quantum-mechanical property of a perfect crystal. An extrinsic mechanism, skew scattering from disorder, tends to dominate the AHE in highly conductive ferromagnets. The full modern semiclassical treatment of the AHE is reviewed which incorporates an anomalous contribution to wave-packet group velocity due to momentum-space Berry curvatures and correctly combines the roles of intrinsic and extrinsic (skew-scattering and side-jump) scattering-related mechanisms. In addition, more rigorous quantum-mechanical treatments based on the Kubo and Keldysh formalisms are reviewed, taking into account multiband effects, and demonstrate the equivalence of all three linear response theories in the metallic regime. Building on results from recent experiment and theory, a
GEO Population Estimates using Optical Survey Data
NASA Technical Reports Server (NTRS)
Barker, Edwin S.; Matney, Mark J.
2007-01-01
/CTIO, Astronomical Institute University of Bern, Boeing LTS / AMOS, Keldysh Institute of Applied Mathematics) at different longitudes. Complete observational coverage over periods of days to months will provide a better understanding of the properties, such as solar radiation pressure effects on orbital elements, size, shape, attitude, color variations, and spectral characteristics. Results from recent observational programs will be summarized, and includes a description of the orbit elements prediction processes, a summary of the metric tracking performance, and some photometric characteristics of this class of debris.
Strong-field and attosecond physics in solids
Ghimire, Shambhu; Ndabashimiye, Georges; DiChiara, Anthony D.; Sistrunk, Emily; Stockman, Mark I.; Agostini, Pierre; DiMauro, Louis F.; Reis, David A.
2014-10-08
We review the status of strong-field and attosecond processes in bulk transparent solids near the Keldysh tunneling limit. For high enough fields and low-frequency excitations, the optical and electronic properties of dielectrics can be transiently and reversibly modified within the applied pulse. In Ghimire et al (2011 Phys. Rev. Lett. 107 167407) non-parabolic band effects were seen in photon-assisted tunneling experiments in ZnO crystals in a strong mid-infrared field. Using the same ZnO crystals, Ghimire et al (2011 Nat. Phys. 7 138–41) reported the first observation of non-pertubative high harmonics, extending well above the bandgap into the vacuum ultraviolet. Recent experiments by Schubert et al (2014 Nat. Photonics 8 119–23) showed a carrier envelope phase dependence in the harmonic spectrum in strong-field 30 THz driven GaSe crystals which is the most direct evidence yet of the role of sub-cycle electron dynamics in solid-state harmonic generation. The harmonic generation mechanism is different from the gas phase owing to the high density and periodicity of the crystal. For example, this results in a linear dependence of the high-energy cutoff with the applied field in contrast to the quadratic dependence in the gas phase. Sub-100 attosecond pulses could become possible if the harmonic spectrum can be extended into the extreme ultraviolet (XUV). Here we report harmonics generated in bulk MgO crystals, extending to $\\sim 26$ eV when driven by ~35 fs, 800 nm pulses focused to a ~1 VÅ$^{-1}$ peak field. The fundamental strong-field and attosecond response also leads to Wannier–Stark localization and reversible semimetallization as seen in the sub-optical cycle behavior of XUV absorption and photocurrent experiments on fused silica by Schiffrin et al (2013 Nature 493 70–4) and Schultze et al (2013 Nature 493 75–8). These studies are advancing our understanding of fundamental strong-field and attosecond physics in solids with potential applications
NASA Astrophysics Data System (ADS)
Rylyuk, V. M.
2016-05-01
Within the framework of the quasistationary quasienergy state (QQES) formalism, the tunneling and multiphoton ionization of atoms and ions subjected to a perturbation by a high intense laser radiation field of an arbitrary polarization and a constant magnetic field are considered. On the basis of the exact solution of the Schrödinger equation and the Green's function for the electron moving in an arbitrary laser field and crossed constant electric and magnetic fields, the integral equation for the complex quasienergy and the energy spectrum of the ejected electron are derived. Using the "imaginary-time" method, the extremal subbarrier trajectory of the photoelectron moving in a nonstationary laser field and a constant magnetic field are considered. Within the framework of the QQES formalism and the quasiclassical perturbation theory, ionization rates when the Coulomb interaction of the photoelectron with the parent ion is taken into account at arbitrary values of the Keldysh parameter are derived. The high accuracy of rates is confirmed by comparison with the results of numerical calculations. Simple analytical expressions for the ionization rate with the Coulomb correction in the tunneling and multiphoton regimes in the case of an elliptically polarized laser beam propagating at an arbitrary angle to the constant magnetic field are derived and discussed. The limits of small and large magnetic fields and low and high frequency of a laser field are considered in details. It is shown that in the presence of a nonstationary laser field perturbation, the constant magnetic field may either decrease or increase the ionization rate. The analytical consideration and numerical calculations also showed that the difference between the ionization rates for an s electron in the case of right- and left-elliptically polarized laser fields is especially significant in the multiphoton regime for not-too-high magnetic fields and decreases as the magnetic field increases. The paper
Russian Internet: Graduated from the Moscow State University
NASA Astrophysics Data System (ADS)
Gaina, Alex B.
2005-09-01
The purpose of the internet proceeding is 1) To give a complete list of publications of the Astronomer V.A.Albitzky (V.A.Albitzkij, b. 1892, Kishinev- d. 1952, Simeiz), graduated from the Moscow State University in 1916. Two photo of the astronomer are placed: http://upmsu.phys.msu.ru/1977/gaina/Albitzky.jpg and http://upmsu.phys.msu.ru/1977/gaina/Albitzky1.jpg 2) to make a review of the problem of Bound States in Black Holes evaporation. 3) A report on the works of the school "Quantum Particles in intensive fields" (Chisinau (Kishinev), 5-9 May, 1985), with photographs (see: http://upmsu.phys.msu.ru/1977/gaina/Out2.jpg) is added. In 1987 at the Shtiintsa eds. (Kishinev) a book: "Quantum processes in intensive fields" (Russian title: "Kvantovyie processy v intensivnyh polyah"), Kishinev Izdatel Shtiintsa, 1987 was published with lectures of the school held by the followuing scientists: Keldysh, L.V., Vaitkus, Yu.Yu., Khadzhi, P.I. et al., Mazets, T.F. et al., Bogolyubov, N.N. Jr. et al., Laptinskaya T.V. et al., Aktsipetrov, O.A., et al., Bobrysheva, A.I. et al., Buzdin, A.I., Golant K.M. et al., Bagrov, V.G. et al., Oleinik, V.P., Borisov, A.V. et al., Rodionov, V.N. et al., Teryeaev, O.V., Gal'tsov, D.V., Buchbinder, I.L. et al., Odintsov, S.D., Zhuk, A.I. The abstracts of the Lectures book can be found at ADS NASA 4) A report on a glory, observed by author in 1988 in the airship, around the umbra of the airship on clouds, flying above Crimea from Yerevan to Chisinau on October 1988, after the finish of the All Union Gravitational Conference held in this city is given. A Photo of the City of Yerevan during the Conference is placed: http://upmsu.phys.msu.ru/1977/gaina/Yerevan_88.jpg
NASA Astrophysics Data System (ADS)
Onuma, Takeyoshi; Chichibu, Shigefusa F.; Aoyama, Toyomi; Nakajima, Kiyomi; Ahmet, Parhat; Azuhata, Takashi; Chikyow, Toyohiro; Sota, Takayuki; Nagahama, Shin-ichi; Mukai, Takashi
2003-12-01
Optical and structural properties of an InGaN double-quantum-well (DQW) laser diode (LD) wafer that lased at 450 nm were investigated to discuss an enormous impact of a polarization-induced electric field on the recombination dynamics in InGaN quantum structures. The quantum-well (QW) structure was shown to have the well thickness as thin as approximately 1 nm and InN molar fraction x of approximately 14%. The gross effective electric field in the QW (FQW) was estimated to be 490 kV/cm from the Franz-Keldysh oscillation (FKO) period in the electroreflectance (ER) spectrum, implying that an internal piezoelectric field (Fpiz) of approximately 1.4 MV/cm was cancelled by the pn junction built-in field (Fbi) and Coulomb screening due to carriers in the DQW. The magnitude of FQW can be further weakened by applying reverse bias (VR) on the junction; the decrease in the photoluminescence (PL) lifetime at low temperature measured under VR was explained to be due to a recovery of electron-hole wavefunction overlap for small VR (|VR|<4 V), and due mainly to the tunneling escape of carriers through the barriers for larger VR. By applying an appropriate VR smaller than 4 V, electron-hole wavefunction overlap, which had been separated vertically along the c-axis due to quantum-confined Stark effect, could be partially recovered, and then the time-resolved PL signals exhibited a less-pronounced stretched exponential decay, giving a scaling parameter (β) of 0.85 and effective in-plane localization depth (E0) of 40-50 meV for the spontaneous emission. These values were closer to those of much homogeneous QWs compared to those reported previously for InGaN QWs having similar InN molar fractions. The use of very thin QWs is considered to bring easier Coulomb screening of FQW and population inversion under high excitation conditions.
Optical Absorption in Liquid Semiconductors
NASA Astrophysics Data System (ADS)
Bell, Florian Gene
An infrared absorption cell has been developed which is suitable for high temperature liquids which have absorptions in the range .1-10('3) cm('-1). The cell is constructed by clamping a gasket between two flat optical windows. This unique design allows the use of any optical windows chemically compatible with the liquid. The long -wavelength limit of the measurements is therefore limited only by the choice of the optical windows. The thickness of the cell can easily be set during assembly, and can be varied from 50 (mu)m to .5 cm. Measurements of the optical absorption edge were performed on the liquid alloy Se(,1-x)Tl(,x) for x = 0, .001, .002, .003, .005, .007, and .009, from the melting point up to 475(DEGREES)C. The absorption was found to be exponential in the photon energy over the experimental range from 0.3 eV to 1.2 eV. The absorption increased linearly with concentration according to the empirical relation (alpha)(,T)(h(nu)) = (alpha)(,1) + (alpha)(,2)x, and the absorption (alpha)(,1) was interpreted as the absorption in the absence of T1. (alpha)(,1) also agreed with the measured absorption in 100% Se at corresponding temperatures and energies. The excess absorption defined by (DELTA)(alpha) = (alpha)(,T)(h(nu))-(alpha)(,1) was interpreted as the absorption associated with Tl and was found to be thermally activated with an activation energy E(,t) = 0.5 eV. The exponential edge is explained as absorption on atoms immersed in strong electric fields surrounding ions. The strong fields give rise to an absorption tail similar to the Franz-Keldysh effect. A simple calculation is performed which is based on the Dow-Redfield theory of absorption in an electric field with excitonic effects included. The excess absorption at low photon energies is proportional to the square of the concentration of ions, which are proposed to exist in the liquid according to the relation C(,i) (PROPORTIONAL) x(' 1/2)(.)e('-E)t('/kT), which is the origin of the thermal activation
Mongolian-Russian cooperation at the Khureltogoot observatory in the ISON project framework
NASA Astrophysics Data System (ADS)
Tungalag, Namkhai; Rentsenmyagmar, Buyankhishig; Turmunkh, Bayarbat; Tsogt-Ochir, Shijirbayar; Molotov, Igor; Voropaev, Viktor; Kouprianov, Vladimir; Krugly, Yury; Schmalz, Sergey; Pozanenko, Aleksey
2014-09-01
Since autumn 2012, the Research Center of Astronomy and Geophysics, Academy of Sciences of Mongolia, in collaboration with the International Scientific Optical Network (ISON) coordinated by the Keldysh Institute for Applied Mathematics (KIAM), Russian Academy of Sciences, have conducted a large number of astronomical observations of space debris, asteroids, and the optical afterglows of gamma-ray bursts (GRBs) at the new facility of the Khureltogoot observatory near Ulaanbaatar. To the date, ISON joins 35 observation facilities with 80 telescopes of apertures from 12.5 cm to 2.6 m in 15 countries and carries out research on space debris, asteroids, and GRBs. 8.4 million measurements in 1.21 million tracklets of about 4000 Earth-orbiting objects were collected by the ISON network in 2013. It is planned that a part of the orbital data will be accessible via a UN-hosted web page in 2014. A new pavilion was built at Khureltogoot during 2012 to initiate collaboration with ISON. Since November 2012, observations began with the VT-78a 19.2 cm telescopes, with a field of view of 7×7 degrees on a robotic WS-180 mount. The telescope is controlled by the CHAOS TCS software; CCD image processing is done using the APEX II software platform developed within the ISON project. This telescope provides extended surveys of a visible part of the geostationary ring from 0 to 20 degrees inclination, with up to 15 thousand measurements of 500 to 700 objects per night. The limiting magnitude is 14 mag for 10 s exposure time, while the time span of individual tracklets is up to several hours. These surveys help KIAM to increase the accuracy of geostationary Earth-orbit (GEO) object orbits for conjunction analysis, to detect maneuvers of active satellites, and to assist in maintaining the orbits of GEO objects in clusters. Moreover, many HEO objects are detected as a by-product. Since November 2013, a new 40 cm telescope, ORI-40 with the field of view of 2.3×2.3 degrees on a robotic WS
Introduction to Nonequilibrium Statistical Mechanics with Quantum Field Theory
NASA Astrophysics Data System (ADS)
Kita, T.
2010-04-01
In this article, we present a concise and self-contained introduction to nonequilibrium statistical mechanics with quantum field theory by considering an ensemble of interacting identical bosons or fermions as an example. Readers are assumed to be familiar with the Matsubara formalism of equilibrium statistical mechanics such as Feynman diagrams, the proper self-energy, and Dyson's equation. The aims are threefold: (i) to explain the fundamentals of nonequilibrium quantum field theory as simple as possible on the basis of the knowledge of the equilibrium counterpart; (ii) to elucidate the hierarchy in describing nonequilibrium systems from Dyson's equation on the Keldysh contour to the Navier-Stokes equation in fluid mechanics via quantum transport equations and the Boltzmann equation; (iii) to derive an expression of nonequilibrium entropy that evolves with time. In stage (i), we introduce nonequilibrium Green's function and the self-energy uniquely on the round-trip Keld ysh contour, thereby avoiding possible confusions that may arise from defining multiple Green's functions at the very beginning. We try to present the Feynman rules for the perturbation expansion as simple as possible. In particular, we focus on the self-consistent perturbation expansion with the Luttinger-Ward thermodynamic functional, i.e., Baym's Phi-derivable approximation, which has a crucial property for nonequilibrium systems of obeying various conservation laws automatically. We also show how the two-particle correlations can be calculated within the Phi-derivable approximation, i.e., an issue of how to handle the ``Bogoliubov-Born-Green-Kirkwood-Yvons (BBGKY) hierarchy''. Aim (ii) is performed through successive reductions of relevant variables with the Wigner transformation, the gradient expansion based on the Groenewold-Moyal product, and Enskog's expansion from local equilibrium. This part may be helpful for convincing readers that nonequilibrium systems ca n be handled
Strong-field and attosecond physics in solids
NASA Astrophysics Data System (ADS)
Ghimire, Shambhu; Ndabashimiye, Georges; DiChiara, Anthony D.; Sistrunk, Emily; Stockman, Mark I.; Agostini, Pierre; DiMauro, Louis F.; Reis, David A.
2014-10-01
We review the status of strong-field and attosecond processes in bulk transparent solids near the Keldysh tunneling limit. For high enough fields and low-frequency excitations, the optical and electronic properties of dielectrics can be transiently and reversibly modified within the applied pulse. In Ghimire et al (2011 Phys. Rev. Lett. 107 167407) non-parabolic band effects were seen in photon-assisted tunneling experiments in ZnO crystals in a strong mid-infrared field. Using the same ZnO crystals, Ghimire et al (2011 Nat. Phys. 7 138-41) reported the first observation of non-pertubative high harmonics, extending well above the bandgap into the vacuum ultraviolet. Recent experiments by Schubert et al (2014 Nat. Photonics 8 119-23) showed a carrier envelope phase dependence in the harmonic spectrum in strong-field 30 THz driven GaSe crystals which is the most direct evidence yet of the role of sub-cycle electron dynamics in solid-state harmonic generation. The harmonic generation mechanism is different from the gas phase owing to the high density and periodicity of the crystal. For example, this results in a linear dependence of the high-energy cutoff with the applied field in contrast to the quadratic dependence in the gas phase. Sub-100 attosecond pulses could become possible if the harmonic spectrum can be extended into the extreme ultraviolet (XUV). Here we report harmonics generated in bulk MgO crystals, extending to ˜ 26 eV when driven by ˜35 fs, 800 nm pulses focused to a ˜1 VÅ-1 peak field. The fundamental strong-field and attosecond response also leads to Wannier-Stark localization and reversible semimetallization as seen in the sub-optical cycle behavior of XUV absorption and photocurrent experiments on fused silica by Schiffrin et al (2013 Nature 493 70-4) and Schultze et al (2013 Nature 493 75-8). These studies are advancing our understanding of fundamental strong-field and attosecond physics in solids with potential applications for compact
Bulk Laser Material Modification: Towards a Kerfless Laser Wafering Process
NASA Astrophysics Data System (ADS)
LeBeau, James
Due to the ever increasing relevance of finer machining control as well as necessary reduction in material waste by large area semiconductor device manufacturers, a novel bulk laser machining method was investigated. Because the cost of silicon and sapphire substrates are limiting to the reduction in cost of devices in both the light emitting diode (LED) and solar industries, and the present substrate wafering process results in >50% waste, the need for an improved ingot wafering technique exists. The focus of this work is the design and understanding of a novel semiconductor wafering technique that utilizes the nonlinear absorption properties of band-gapped materials to achieve bulk (subsurface) morphological changes in matter using highly focused laser light. A method and tool was designed and developed to form controlled damage regions in the bulk of a crystalline sapphire wafer leaving the surfaces unaltered. The controllability of the subsurface damage geometry was investigated, and the effect of numerical aperture of the focusing optic, energy per pulse, wavelength, and number of pulses was characterized for a nanosecond pulse length variable wavelength Nd:YAG OPO laser. A novel model was developed to describe the geometry of laser induced morphological changes in the bulk of semiconducting materials for nanosecond pulse lengths. The beam propagation aspect of the model was based on ray-optics, and the full Keldysh multiphoton photoionization theory in conjuncture with Thornber's and Drude's models for impact ionization were used to describe high fluence laser light absorption and carrier generation ultimately resulting in permanent material modification though strong electron-plasma absorption and plasma melting. Although the electron-plasma description of laser damage formation is usually reserved for extremely short laser pulses (<20 ps), this work shows that it can be adapted for longer pulses of up to tens of nanoseconds. In addition to a model
Strong correlations in gravity and biophysics
NASA Astrophysics Data System (ADS)
Krotov, Dmitry
The unifying theme of this dissertation is the use of correlations. In the first part (chapter 2), we investigate correlations in quantum field theories in de Sitter space. In the second part (chapters 3,4,5), we use correlations to investigate a theoretical proposal that real (observed in nature) transcriptional networks of biological organisms are operating at a critical point in their phase diagram. In chapter 2 we study the infrared dependence of correlators in various external backgrounds. Using the Schwinger-Keldysh formalism we calculate loop corrections to the correlators in the case of the Poincare patch and the complete de Sitter space. In the case of the Poincare patch, the loop correction modifies the behavior of the correlator at large distances. In the case of the complete de Sitter space, the loop correction has a strong dependence on the infrared cutoff in the past. It grows linearly with time, suggesting that at some point the correlations become strong and break the symmetry of the classical background. In chapter 3 we derive the signatures of critical behavior in a model organism, the embryo of Drosophila melanogaster. They are: strong correlations in the fluctuations of different genes, a slowing of dynamics, long range correlations in space, and departures from a Gaussian distribution of these fluctuations. We argue that these signatures are observed experimentally. In chapter 4 we construct an effective theory for the zero mode in this system. This theory is different from the standard Landau-Ginsburg description. It contains gauge fields (the result of the broken translational symmetry inside the cell), which produce observable contributions to the two-point function of the order parameter. We show that the behavior of the two-point function for the network of N genes is described by the action of a relativistic particle moving on the surface of the N - 1 dimensional sphere. We derive a theoretical bound on the decay of the correlations and
Increase in the energy density of the pinch plasma in 3D implosion of quasi-spherical wire arrays
Aleksandrov, V. V.; Gasilov, V. A.; Grabovski, E. V.; Gritsuk, A. N. Laukhin, Ya. N.; Mitrofanov, K. N.; Oleinik, G. M.; Ol’khovskaya, O. G.; Sasorov, P. V.; Smirnov, V. P.; Frolov, I. N.; Shevel’ko, A. P.
2014-12-15
Keldysh Institute of Applied Mathematics, Russian Academy of Sciences.
Non-equilibrium STLS approach to transport properties of single impurity Anderson model
Rezai, Raheleh Ebrahimi, Farshad
2014-04-15
In this work, using the non-equilibrium Keldysh formalism, we study the effects of the electron–electron interaction and the electron-spin correlation on the non-equilibrium Kondo effect and the transport properties of the symmetric single impurity Anderson model (SIAM) at zero temperature by generalizing the self-consistent method of Singwi, Tosi, Land, and Sjolander (STLS) for a single-band tight-binding model with Hubbard type interaction to out of equilibrium steady-states. We at first determine in a self-consistent manner the non-equilibrium spin correlation function, the effective Hubbard interaction, and the double-occupancy at the impurity site. Then, using the non-equilibrium STLS spin polarization function in the non-equilibrium formalism of the iterative perturbation theory (IPT) of Yosida and Yamada, and Horvatic and Zlatic, we compute the spectral density, the current–voltage characteristics and the differential conductance as functions of the applied bias and the strength of on-site Hubbard interaction. We compare our spectral densities at zero bias with the results of numerical renormalization group (NRG) and depict the effects of the electron–electron interaction and electron-spin correlation at the impurity site on the aforementioned properties by comparing our numerical result with the order U{sup 2} IPT. Finally, we show that the obtained numerical results on the differential conductance have a quadratic universal scaling behavior and the resulting Kondo temperature shows an exponential behavior. -- Highlights: •We introduce for the first time the non-equilibrium method of STLS for Hubbard type models. •We determine the transport properties of SIAM using the non-equilibrium STLS method. •We compare our results with order-U2 IPT and NRG. •We show that non-equilibrium STLS, contrary to the GW and self-consistent RPA, produces the two Hubbard peaks in DOS. •We show that the method keeps the universal scaling behavior and correct
Ultrafast and nonlinear optics in carbon nanomaterials.
Kono, Junichiro
2013-02-01
Carbon-based nanomaterials—single-wall carbon nanotubes (SWCNTs) and graphene, in particular—have emerged in the last decade as novel low-dimensional systems with extraordinary properties. Because they are direct-bandgap systems, SWCNTs are one of the leading candidates to unify electronic and optical functions in nanoscale circuitry; their diameter-dependent bandgaps can be utilized for multi-wavelength devices. Graphene's ultrahigh carrier mobilities are promising for high-frequency electronic devices, while, at the same time, it is predicted to have ideal properties for terahertz generation and detection due to its unique zero-gap, zero-mass band structure. There have been a large number of basic optical studies on these materials, but most of them were performed in the weak-excitation, quasi-equilibrium regime. In order to probe and assess their performance characteristics as optoelectronic materials under device-operating conditions, it is crucial to strongly drive them and examine their optical properties in highly non-equilibrium situations and with ultrashot time resolution. In this section, the reader will find the latest results in this rapidly growing field of research. We have assembled contributions from some of the leading experts in ultrafast and nonlinear optical spectroscopy of carbon-based nanomaterials. Specific topics featured include: thermalization, cooling, and recombination dynamics of photo-generated carriers; stimulated emission, gain, and amplification; ultrafast photoluminescence; coherent phonon dynamics; exciton–phonon and exciton–plasmon interactions; exciton–exciton annihilation and Auger processes; spontaneous and stimulated emission of terahertz radiation; four-wave mixing and harmonic generation; ultrafast photocurrents; the AC Stark and Franz–Keldysh effects; and non-perturbative light–mater coupling. We would like to express our sincere thanks to those who contributed their latest results to this special section
Recent progress of probing correlated electron states by point contact spectroscopy
NASA Astrophysics Data System (ADS)
Lee, Wei-Cheng; Greene, Laura H.
2016-09-01
We review recent progress in point contact spectroscopy (PCS) to extract spectroscopic information out of correlated electron materials, with the emphasis on non-superconducting states. PCS has been used to detect bosonic excitations in normal metals, where signatures (e.g. phonons) are usually less than 1% of the measured conductance. In the superconducting state, point contact Andreev reflection (PCAR) has been widely used to study properties of the superconducting gap in various superconductors. It has been well-recognized that the corresponding conductance can be accurately fitted by the Blonder–Tinkham–Klapwijk (BTK) theory in which the AR occurring near the point contact junction is modeled by three parameters; the superconducting gap, the quasiparticle scattering rate, and a dimensionless parameter, Z, describing the strength of the potential barrier at the junction. AR can be as large as 100% of the background conductance, and only arises in the case of superconductors. In the last decade, there have been more and more experimental results suggesting that the point contact conductance could reveal new features associated with the unusual single electron dynamics in non-superconducting states, shedding a new light on exploring the nature of the competing phases in correlated materials. To correctly interpret these new features, it is crucial to re-examine the modeling of the point contact junctions, the formalism used to describe the single electron dynamics particularly in point contact spectroscopy, and the physical quantity that should be computed to understand the conductance. We will summarize the theories for point contact spectroscopy developed from different approaches and highlight these conceptual differences distinguishing point contact spectroscopy from tunneling-based probes. Moreover, we will show how the Schwinger–Kadanoff–Baym–Keldysh (SKBK) formalism together with the appropriate modeling of the nano-scale point contacts randomly
NASA Astrophysics Data System (ADS)
Roque, C.; Simões, M.; Lourenço, N.; Pinto de Abreu, M.
2009-04-01
The West Madeira Abyssal Plain is located in the eastern North Atlantic off Madeira Islands, forming part of the Canary Basin and reaching a mean water depth of 5300 m. This region is also located within Africa plate at about 500 km southwards from the Açores-Gibraltar plate boundary, and for that reason lacks seismic activity. Although this region being located in an intraplate setting, the presence of faulted sediments was reported in several works published during the eighties of last century following a study conducted in late 1970s to evaluate the feasibility of disposal of high-level radioactive wastes in the ocean. According these works, the Madeira Abyssal Plain sediments are cut by many normal growth faults and this deformation is a result of compaction and dewatering of the sediments. Evidences of tectonic deformation of oceanic sediments in intraplate settings are uncommon, but folded sediments and reverse faults extending into the basement, were recognized in the equatorial Indian Ocean and in the West African continental margin. Recently, during 2006 multi-channel seismic reflection and multibeam swath bathymetry surveys were carried out in the West Madeira Abyssal Plain by EMEPC in order to prepare the Portuguese proposal for the extension of the continental shelf. The seismic lines were acquired onboard R/V Akademik Shatskiy using a source of 5720 cu in bolt gun array, cable length of 7950 m and shot interval of 50.00 m. The multibeam swath bathymetry was acquired onboard NRP Gago Coutinho, and allowed a high resolution mapping of the main geomorphological features. The multichannel seismic lines, oriented WNW-ESE, image the Madeira island lower slope located at about 4000 m water depth and the almost flat abyssal plain at about 5300 m water depth. These seismic lines show a thick sedimentary succession that reaches a maximum thickness of about 1.5 sec twt in the deepest parts of the West Madeira Abyssal Plain, overlying an irregular diffractive
Giant mudwaves in the Northern Argentine Basin: born and buried by bottom currents
NASA Astrophysics Data System (ADS)
Borisov, Dmitrii; Murdmaa, Ivar; Ivanova, Elena; Levchenko, Oleg
2014-05-01
New sedimentary records and very high resolution seismic profiles collected during four cruises of the RV "Akademik Ioffe" (2011-2013) were correlated with seismic, multibeam and coring data obtained during cruises of the RV "Robert Conrad", "Knorr", "Meteor". A complex analysis of the geological-geophysical data revealed an extensive field of giant mudwaves (48 000 km2) in the northwestern Argentine Basin, South Atlantic. The symmetric waves up to 60 m in height and 4000 m in wavelength are oriented roughly parallel to contours. They partly cover the Santa Catarina Plateau and extend through the Santos Basin to the Sao Paulo Plateau. The mudwaves field is traced at the depth range from 3400 to 4000 m and divided into buried (northern) and non-buried (southern) parts. The non-buried sediment waves cover the surface of the huge drift in the Santa Catarina Plateau. The wave height increases from the drift summit to its flanks and decreases at the foot. Two cores retrieved from the drift top and its northern flank recovered muddy contourites with a greater amount of silt-size material in the core from the drift flank. The age of the recovered sediments is at least 130 ka. In the northern Santos basin, the sediment waves are buried under a large lens-like sediment body (drift?) inclined at the margins. Cores obtained from the buried part of the mudwaves field recovered an intercalation of hemipelagic clay and silty-clay contourite. The age of recovered sediments does not exceed 150 ka (Bleil et al., 1993). Contourites deposition in the study area is related to the activity of the Antarctic bottom water (AABW) contour current. The AABW flow is considered to be divided into two branches by the Santa Catarina Plateau. We suggest that this topographic obstacle causes a flow velocity increase. Wave height and grain-size variations indicate higher bottom current velocities at the plateau flanks and relative tranquil conditions at the flat summit of the plateau. The symmetric
Geochemistry of rare and minor elements in sediments from Brazil Basin of Atlantic Ocean
NASA Astrophysics Data System (ADS)
Vvedenskaya, Irina; Dubinin, Alexander
2010-05-01
This paper reviews the features of the rare and minor elements in the sediment samples recovered from the Brazil Basin at the location of the Station No. 1537 in the Atlantic Ocean during the 18th cruise of the Research Vessel "Akademik Sergey Vavilov". The depth of the sediment column is 470 cm. The sediments are represented by the oxidized miopelagic clay (0-305 cm) which are underlain by the thin bedded Ethmodiscus diatom oozes (305-470 cm). The brown miopelagic clay (0.09-1.25% СаСО3, 0.05-0.28% Сorganic) predominately consist of the clay minerals (91-97%). The top section sediments also include some terrigenous clastic sandy-silt minerals (1-5%), diatoms (up to 2%), manganese micronodules (approx. 1%), occasional spicules, radiolarian, coccoliths and marine fossil fragments. The transition to the lower diatom oozes is associated with the lens-shape structures and increase in the content of diatoms in clay. The age of sediments at the station No. 1537 is Late Pleistocene. Presence of thin bedded Ethmodiscus oozes is an indirect evidence of re-deposition of the sediments in the central part of the Brazil Basin The chemical composition has been analyzed on 37 core samples recovered from the column. These core samples have been used to define the content of the chemical composition as well as the rare and minor elements. The manganese content in the top section of the miopelagic clay varies insignificantly and value is close 0.46%. The rare and minor elements content in the miopelagic clay is quite stable. The sharp increase in manganese content (to 1.16%) as well as in that of the minor elements such as Co, Cu, Ni, Mo and Tl are observed at the 305-308 cm horizon which corresponds to the bottom of the miopelagic clay. Than, the manganese content decreases to reach its minimum value (0.20%) immediately below this horizon. With further depth increase, the content of manganese starts rising again reaces its maximum value of 2.31% at the 405-407 cm horizon. The
NASA Astrophysics Data System (ADS)
Mahfouzi, Farzad
ferromagnet (FM). I show that this could be due to the existence of Rashba spin-orbit coupling (SOC) at the interface of the FM and insulator. Assuming that the measured signals are quantum mechanical effect where a solution to the time dependent Schrodinger equation is required, I use Keldysh Green function formalism to introduce a "multi-photon" approach which takes into account the effects of time-dependent term exactly up to scatterings from a finite number of photons. We then proceed to find the corresponding Green function numerically using a recursive method which allows us to increase the size of the system significantly. We also implement other approximations such as adiabatic and rotating frame approaches and compared them with our approach. In Chapter 4, I investigate the spin and charge pumping from a precessing magnetization attached to the edge of a 2-dimensional topological insulator (2DTI). We show that, in this system a huge spin current (or voltage signal if the FM covers only one edge) can be pumped for very small cone angles of the precessing FM (proportional to the intensity of the applied microwave). In Chapter 5 I present the third project in this field of research, where, I investigated the pumping from FM attached to a 3-dimensional TI. Spin-transfer torque: Presented in Chapter 6, in this work I investigate the torque induced by a flow of spin-polarized current into a FM and check the condition in which it can cause the magnetization to flip. Motivated by recent experimental developments in the field, here I consider systems with strong SOC such as TIs within a magnetic tunnel junction (MTJ) heterostructure. In the theoretical part I show the correct way (as opposed to the conventional approach used in some theoretical works which suffers from violation of the gauge invariance) to calculate linear-response torque to the external applied voltage and for the numerical calculation I adopted a parallelized adaptive integration algorithm in order to take
NASA Astrophysics Data System (ADS)
Calzetta, E. A.; Hu, B. L.; Mazzitelli, Francisco D.
2001-10-01
In this report we introduce the basic techniques (of the closed-time-path (CTP) coarse-grained effective action (CGEA)) and ideas (scaling, coarse-graining and backreaction) behind the treatment of quantum processes in dynamical background spacetimes and fields. We show how they are useful for the construction of renormalization group (RG) theories for studying these nonequilibrium processes and discuss the underlying issues. Examples are drawn from quantum field processes in an inflationary universe, semiclassical cosmology and stochastic gravity. In Part I (Sections /2, /3) we begin by establishing a relation between scaling and inflation, and show how eternal inflation (where the scale factor of the universe grows exponentially) can be treated as static critical phenomena, while a `slow-roll' or power-law inflation can be treated as dynamical critical phenomena. In Part II (Sections /4, /5) we introduce the key concepts in open systems and discuss the relation of coarse-graining and backreaction. We recount how the (in-out, or Schwinger-DeWitt) CGEA devised by Hu and Zhang can be used to treat some aspects of the effects of the environment on the system. This is illustrated by the stochastic inflation model where quantum fluctuations appearing as noise backreact on the inflaton field. We show how RG techniques can be usefully applied to obtain the running of coupling constants in the inflaton field, followed by a discussion of the cosmological and theoretical implications. In Part III (Sections /6-/8) we present the CTP (in-in, or Schwinger-Keldysh) CGEA introduced by Hu and Sinha. We show how to calculate perturbatively the CTP CGEA for the λΦ4 model. We mention how it is useful for calculating the backreaction of environmental fields on the system field (e.g. light on heavy, fast on slow) or one sector of a field on another (e.g. high momentum modes on low, inhomogeneous modes on homogeneous), and problems in other areas of physics where this method can be
Alidoust, Mohammad; Halterman, Klaus
2015-03-28
Using a spin-parameterized quasiclassical Keldysh-Usadel technique, we theoretically study supercurrent transport in several types of diffusive ferromagnetic (F)/superconducting (S) configurations with differing magnetization textures. We separate out the even- and odd-frequency components of the supercurrent within the low proximity limit and identify the relative contributions from the singlet and triplet channels. We first consider inhomogeneous one-dimensional Josephson structures consisting of a uniform bilayer magnetic S/F/F/S structure and a trilayer S/F/F/F/S configuration, in which case the outer F layers can have either a uniform or conical texture relative to the central uniform F layer. Our results demonstrate that for supercurrents flowing perpendicular to the F/F interfaces, incorporating a conical texture yields the most effective way to observe the signatures of long-ranged spin-triplet supercurrents. We also consider three different types of finite-sized two-dimensional magnetic structures subjected to an applied magnetic field normal to the junction plane: a S/F/S junction with uniform magnetization texture and two S/F/F/S configurations with differing F/F bilayer arrangements. In one case, the F/F interface is parallel with the S/F junction interfaces while in the other case, the F/F junction is oriented perpendicular to the S/F interfaces. We then discuss the proximity vortices and corresponding spatial maps of currents inside the junctions. For the uniform S/F/S junction, we analytically calculate the magnetic field induced supercurrent and pair potential in both the narrow and wide junction regimes, thus providing insight into the variations in the Fraunhofer diffraction patterns and proximity vortices when transitioning from a wide junction to a narrow one. Our extensive computations demonstrate that the induced long-range spin-triplet supercurrents can deeply penetrate uniform F/F bilayers when spin-singlet supercurrents flow parallel to the
Catalogue of space objects and events as a powerful tool for scientific researches on space debris
NASA Astrophysics Data System (ADS)
Agapov, V.; Stepanyants, V.; Tuchin, A.; Khutorovsky, Z.
Wide work on developing and maintenance of the Catalogue of scientific information on space objects and events is continuing at the Keldysh Institute of Applied Mathematics. The work is making in cooperation with Russian company "Space information analytical systems" (KIA Systems). Powerful software tool is developed by now including:- informational core (relational database in RDBMS Oracle 8i environment)with special tools for automatic initial processing and systematization ofdata- software complex for orbital modeling and space objects and eventsdynamical catalogue maintenance- special information - analytical software Informational core covers wide spectrum of data needed for following purposes:- full-scale and high quality modeling of object's motion in near-Earth space(orbital and measurement data, solar flux and geomagnetic indices, Earthrotation parameters etc.)- determination of various events parameters (launches, manoeuvres,fragmentations etc.)- analysis of space debris sources- studying long-term orbital evolution (over several years or tens of years)- other The database is storing huge volume of data including:- optical measurements- TLEs- information about all space launches took place since 1957- information about space missions and programs- manoeuvres- fragmentations- launch sequences for typical orbital insertions- various characteristics for orbital objects (payloads, stages, fragments)- officially released UN and ITU registration data- other By now there are records storing in informational core for more than 28000 orbital objects (both catalogued and not), about all orbital launch attempts since 04.10.1957 (including failed ones), more than 30millions records of orbital information (TLEs, state vectors, polynomial data), more than 200000 optical measurements (normal places) for GEO region objects, calculated data on more than 14 millions of close approaches had taken place during last five years and other data. Software complex for orbital
NASA Astrophysics Data System (ADS)
2014-02-01
On 5 - 6 June 2013, an extended session of the all-institute seminar was held at the Russian Federation State Scientific Center 'Alikhanov Institute for Theoretical and Experimental Physics' (ITEP). It was devoted to the 100th anniversary of the birth of Academician Isaak Yakovlevich Pomeranchuk, the founder of the Theory Department of ITEP. The announced agenda of the session on the ITEP website http://www.itep.ru/rus/Pomeranchuk100.html contained the following reports: (1) Gershtein S S (SRC 'Institute for High Energy Physics', Protvino, Moscow region) "I Ya Pomeranchuk and the large accelerator";(2) Keldysh L V (Lebedev Physical Institute, RAS (FIAN), Moscow) "Dynamic tunneling";(3) Vaks V G (National Research Centre 'Kurchatov Institute' (NRC KI), Moscow) "Brief reminiscences";(4) Smilga A V (Laboratoire Physique Subatomique et des technologies associées, Université de Nantes, France) "Vacuum structure in 3D supersymmetric gauge theories";(5) Khriplovich I B (Budker Institute of Nuclear Physics, SB RAS, Novosibirsk) "Gravitational four-fermion interaction and early Universe dynamics";(6) Dremin I M (FIAN, Moscow) "Elastic scattering of hadrons";(7) Belavin A A (Landau Institute of Theoretical Physics, RAS, Moscow) "Correlators in minimal string models";(8) Voloshin M B (Theoretical Physics Institute, University of Minnesota, USA) "Exotic quarkonium";(9) Nekrasov N A (Institut des hautes études scientifiques (IHES), France) "BPS/CFT correspondence";(10) Zarembo K (Uppsala Universitet, Sweden) "Exact results in supersymmetric theories and AdS/CFT correspondence";(11) Gorsky A S (ITEP, Moscow) "Baryon as a dyon instanton";(12) Blinnikov S I (ITEP, Moscow) "Mirror substance and other models for dark matter";(13) Rubakov V A (Institute for Nuclear Research, RAS, Moscow) "Test-tube Universe";(14) Kancheli O V (ITEP, Moscow) "50 years of reggistics";(15) Shevchenko V I (NRC KI) "In search of the chiral magnetic effect";(16) Kirilin V P (ITEP, Moscow) "Anomalies and
Scaled Strong Field Interactions at Long Wavelengths
NASA Astrophysics Data System (ADS)
Sistrunk, Emily Frances
The strong field regime describes interactions between light and matter where the electric field of the laser is a significant fraction of the binding field of the atom. Short pulsed lasers are capable of producing local fields on the order of the atomic unit of electric field. Under the influence of such strong fields, the ionization regime and electron dynamics are highly dependent on the wavelength used to drive the interaction. Few studies have been performed in the mid-infrared (MIR) spectral range. Using MIR wavelengths, the ponderomotive energy, Up, imposed on the electrons can be a factor of 20 greater than in the visible and near-infrared. Experiments on above threshold ionization (ATI) of cesium, nonsequential ionization (NSI) of noble gases, and high harmonic generation (HHG) in condensed phase media highlight the benefits of performing strong field investigations in the MIR. The photoelectron energy spectrum from above threshold ionization (ATI) of atoms provides details about the strong field interaction. Cesium atoms driven by a 3.6 mum laser indicate that excited states can play a large role in ionization from the ground state. Previous experiments on argon in the near-infrared can be compared to cesium at 3.6 im due to their similar Keldysh-scaling. Unlike argon, the measured ionization yield in cesium saturates at a higher intensity than predicted due to the Stark shift of the ground state. Such shifts have not been detected in argon. The low-lying 6P excited states of cesium produce a strong effect on the photoelectron energy spectrum, resulting in a splitting of each ATI peak. Enhancements in the photoelectron energy spectrum similar to those found in argon are observed in cesium. These enhancements are relatively insensitive to ellipticity of the drive laser. To take advantage of the large ponderomotive energy associated with Mid-IR lasers, ionization of argon, krypton and xenon is studied at 3.6 im. The factor of 20 increase in Up between the
The behaviour of cloud and clear sky brightness in the vicinity of the cloud edge
NASA Astrophysics Data System (ADS)
Bass, L.; Nikolaeva, O.; Kuznetsov, V.; Kokhanovsky, A.
2007-12-01
L.P. Bass1, O.V. Nikolaeva1, V.S.Kuznetsov2, A. A. Kokhanovsky3,4 1Keldysh Institute of Applied Mathematics, Russian Academy of Science Miusskaya Sq. 4,125047 Moscow, Russia 2Research Scientific Center "Kurchatov Institute", Kurchatov Sq. 1, 123182 Moscow, Russia 3Institute of Remote Sensing, Bremen University, Otto Hahn Allee 1 28334 Bremen, Germany 4Institute of Physics, National Academy of Sciences of Belarus, Nezaleznasti Pr. 70 220072 Minsk, Belarus In the solution of remote sensing problems in the framework of the Independent Pixel Approximation (IPA) the horizontal transport of radiation is not taken into account. Therefore, the large errors in the retrieved optical parameters of a medium under study can occur in retrievals for regions, where 3-D radiative transfer effects are of importance (Wen et al, 2007, Titov, 1998). In the present work we analyze the brightness at the edge of a cubic cloud. The energy balance equations within the clear sky-cloud boundary layer are studied. The boundary layer is the domain that includes the vertical boundary of the adjacent pixels with different optical properties. Balance equation connects the radiation fluxes entering into the boundary layer and outgoing from it, and also the amount of energy absorbed in the layer. It is demonstrated that horizontal transport of radiation generates several observable phenomena such as "shadowing" and "brightening" (depending on the Sun position with respect to the cloud and also the area studied). All calculations are performed with the code Raduga-5.1 (Nikolaeva et al., 2005) developed for the computer with the parallel architecture for 1-D, 2-D, 3-D radiative transfer. The code is based on the numerical solution of the integro - differential radiative transfer equation (RTE) with correspondent boundary conditions and prescribed properties of a light scattering medium. Grids with respect to spatial and angular variables are introduced and RTE reduced to the system of the grid
Strongly correlated quantum transport out-of-equilibrium
NASA Astrophysics Data System (ADS)
Dutt, Prasenjit
The revolutionary advances in nanotechnology and nanofabrication have facilitated the precise control and manipulation of mesoscopic systems where quantum effects are pronounced. Quantum devices with tunable gates have made it possible to access regimes far beyond the purview of linear response theory. In particular, the influence of strong voltage and thermal biases has led to the observation of novel phenomena where the non-equilibrium characteristics of the system are of paramount importance. We study transport through quantum-impurity systems in the regime of strong correlations and determine the effects of large temperature and potential gradients on its many-body physics. In Part I of this thesis we focus on the steady-state dynamics of the system, a commonly encountered experimental scenario. For a system consisting of several leads composed of non-interacting electrons, each individually coupled to a quantum impurity with interactions and maintained at different chemical potentials, we reformulate the system in terms of an effective-equilibrium density matrix. This density matrix has a simple Boltzmann-like form in terms of the system's Lippmann-Schwinger (scattering) operators. We elaborate the conditions for this description to be valid based on the microscopic Hamiltonian of the system. We then prove the equivalence of physical observables computed using this formulation with corresponding expressions in the Schwinger-Keldysh approach and provide a dictionary between Green's functions in either scheme. An imaginary-time functional integral framework to compute finite temperature Green's functions is proposed and used to develop a novel perturbative expansion in the interaction strength which is exact in all other system parameters. We use these tools to study the fate of the Abrikosov-Suhl regime on the Kondo-correlated quantum dot due to the effects of bias and external magnetic fields. Next, we expand the domain of this formalism to additionally
PREFACE: Ultrafast and nonlinear optics in carbon nanomaterials
NASA Astrophysics Data System (ADS)
Kono, Junichiro
2013-02-01
Carbon-based nanomaterials—single-wall carbon nanotubes (SWCNTs) and graphene, in particular—have emerged in the last decade as novel low-dimensional systems with extraordinary properties. Because they are direct-bandgap systems, SWCNTs are one of the leading candidates to unify electronic and optical functions in nanoscale circuitry; their diameter-dependent bandgaps can be utilized for multi-wavelength devices. Graphene's ultrahigh carrier mobilities are promising for high-frequency electronic devices, while, at the same time, it is predicted to have ideal properties for terahertz generation and detection due to its unique zero-gap, zero-mass band structure. There have been a large number of basic optical studies on these materials, but most of them were performed in the weak-excitation, quasi-equilibrium regime. In order to probe and assess their performance characteristics as optoelectronic materials under device-operating conditions, it is crucial to strongly drive them and examine their optical properties in highly non-equilibrium situations and with ultrashot time resolution. In this section, the reader will find the latest results in this rapidly growing field of research. We have assembled contributions from some of the leading experts in ultrafast and nonlinear optical spectroscopy of carbon-based nanomaterials. Specific topics featured include: thermalization, cooling, and recombination dynamics of photo-generated carriers; stimulated emission, gain, and amplification; ultrafast photoluminescence; coherent phonon dynamics; exciton-phonon and exciton-plasmon interactions; exciton-exciton annihilation and Auger processes; spontaneous and stimulated emission of terahertz radiation; four-wave mixing and harmonic generation; ultrafast photocurrents; the AC Stark and Franz-Keldysh effects; and non-perturbative light-mater coupling. We would like to express our sincere thanks to those who contributed their latest results to this special section, and the
Essential Spaceflight Dynamics and Magnetospherics
NASA Astrophysics Data System (ADS)
Rauschenbakh, B. V.; Ovchinnikov, M. Yu.; McKenna-Lawlor, S.
2002-12-01
references since if refers to ongoing work in space physics rather than to classical material. Rauschenbakh, Boris Victorovich (1915-2001). Doctor of Technical Science, Member of the Russian Academy of Sciences and the International Academy of Astronautics. One of the founders of practical cosmonautics in Russia. Worked in the `Energia' Enterprise with Sergey Koroljev and later occupied the Chair of Theoretical Mechanics at the Moscow Institute of Physics and Technology. Ovchinnikov, Michael Yurjevich, Doctor of Science in Physics and Mathematics at the Keldysh Institute of Applied Mathematics of the Russian Academy of Sciences and also a Professor at the Moscow Institute of Physics and Technology. Expert in mechanics, spaceflight dynamics and attitude control for small satellites. McKenna-Lawlor, Susan, Emeritus Professor at the National University of Ireland, Maynooth. Guest Professor of the Chinese Academy of Sciences. Doctorate in Space Physics. Director of Space Technology Ireland, Ltd. Pioneering experiments flown on European, American, Russian and Chinese Space Agency Missions. Member of the International Academy of Astronautics. Recipient of the Tsiolkovsky Medal for Cosmonautics. Link: http://www.wkap.nl/prod/b/1-4020-1063-X
First Principles Quantitative Modeling of Molecular Devices
NASA Astrophysics Data System (ADS)
Ning, Zhanyu
In this thesis, we report theoretical investigations of nonlinear and nonequilibrium quantum electronic transport properties of molecular transport junctions from atomistic first principles. The aim is to seek not only qualitative but also quantitative understanding of the corresponding experimental data. At present, the challenges to quantitative theoretical work in molecular electronics include two most important questions: (i) what is the proper atomic model for the experimental devices? (ii) how to accurately determine quantum transport properties without any phenomenological parameters? Our research is centered on these questions. We have systematically calculated atomic structures of the molecular transport junctions by performing total energy structural relaxation using density functional theory (DFT). Our quantum transport calculations were carried out by implementing DFT within the framework of Keldysh non-equilibrium Green's functions (NEGF). The calculated data are directly compared with the corresponding experimental measurements. Our general conclusion is that quantitative comparison with experimental data can be made if the device contacts are correctly determined. We calculated properties of nonequilibrium spin injection from Ni contacts to octane-thiolate films which form a molecular spintronic system. The first principles results allow us to establish a clear physical picture of how spins are injected from the Ni contacts through the Ni-molecule linkage to the molecule, why tunnel magnetoresistance is rapidly reduced by the applied bias in an asymmetric manner, and to what extent ab initio transport theory can make quantitative comparisons to the corresponding experimental data. We found that extremely careful sampling of the two-dimensional Brillouin zone of the Ni surface is crucial for accurate results in such a spintronic system. We investigated the role of contact formation and its resulting structures to quantum transport in several molecular
Complex Airy analysis of photoreflectance spectra for III-V semiconductors
NASA Astrophysics Data System (ADS)
Estrera, J. P.; Duncan, W. M.; Glosser, R.
1994-03-01
ranging from 3 to 4 meV below the band gap, which is similar to excitonic binding energies in this material system. A below-critical-point feature was evident in one GaAs sample at 11 meV below the E0+Δ0 transition. Also, in GaAs we determined the ratio of light and heavy interband effective masses, μLH/μHH, to be 0.6865, which is in good agreement with values determined in previous studies. For bulk InP the band-gap energy was determined to be 1.340+/-0.003 eV, which agreed, within experimental error, with the band-gap energy determined from PL. Below-critical-point features were also found for InP with energies of 4.0 and 3.5 meV below the E0 and E0+Δ0 transitions, respectively. For both GaAs and InP, the surface electric fields determined from the E0 and E0+Δ0 critical points were in agreement within experimental error. For InxGa1-xAs on InP films near lattice-matched conditions, the complex Airy line shape was applied to both intermediate electric field (Franz-Keldysh oscillations) and low-field-like PR spectra illustrating the utility of the complex Airy functional analysis in fitting both simple and complicated PR responses. We found that the band-gap energy from the PR spectral fits to those determined from photoluminescence measurements agreed within experimental error for these InxGa1-xAs films.
NASA Astrophysics Data System (ADS)
Sharkov, E.; Bortnikov, N.; Zinger, T.; Lepekhina3, E.; Sergeev, S.
2009-04-01
Unusually ancient (ranging from ~100 to 300 and even 2230 Ma [5, 6, etc.) and young (~1.2-2 Ma [1] zircons were discovered in the axial Mid-Atlantic Ridge (MAR) zone using U-Pb dating. At first glance, finds of ancient zircons are inconsistent with the general accepted plate tectonics model which suggests the formation of new oceanic crust in the spreading zone of the World Ocean. However, they can be explained by features of the oceanic mantle structure. We have dated 150 grains of zircon by U-Pb SIMS SHRIMP technique, which identified both ancient and young zircons in the same samples of MAR gabbroids from Sierra Leone testing area, Markov Deep, 6oN, dredged during Cruise 10 of R/V "Akademik Ioffe" (2001-2002) and Cruise 22 of R/V "Professor Logachev" (2003) [2]. Zircons were separated from gabbroids in the Markov Deep from depths 3600-3240 and 3900-3600 m. All complexes of the oceanic lithosphere occur on it's slopes: mantle residual ultramafites (harzburgites, lherzolites, and dunites), diverse gabbroids, granodiorites, plagiogranites, dolerites and basalts, including fresh pillow lavas (with chilled glassy margins), and deformed and hydrothermally altered rocks with sulfide mineralization. Studied samples are represented by cataclased and altered leucogabbronorites and one sample of fresh non-cataclased troctolite. Based on SHRIMP U-Pb dating, zircons can be subdivided into two groups: "young" zircon (less than ~2.3 Ma) and "old" zircon (older than ~87 Ma). The young zircon often form subhedral crystals with thin oscillatory zoning and a sectorial structure. It has low U and Th contents (up to 100 μg/g) and extremely low radiogenic lead. Its 238U/206Pb age varied from 0.76 ± 0.04 Ma to 2.28 ± 0.18 Ma. Zircons from nearby plagiogranites define an intermediate age of ~1.2-1.4 Ma [1]. The magmatic nature of young zircon suggests that its age defines the crystallization age of the host magmatic rocks. Ancient zircons define U/Pb ages between the Paleozoic and
Fluidodynamic Processes in Different Regimes of Dilotansy and Compaction
NASA Astrophysics Data System (ADS)
Dmitrievsky, A. N.; Balanyuk, I. E.; Karakin, A. V.; Poveschenko, Yu. A.; Dongaryan, L. Sh.
2003-04-01
FLUIDODYNAMIC PROCESS IN DIFFERENT REGIMES OF DILOTANSY AND COMPACTION A. N. Dmitrievsky(1), I. E. Balanyuk(2), A. V.Karakin, (3), Yu. A. Poveschenko(4), L.Sh. Dongaryan(2) (1) Institute of Oil and Gas Problems, (2) P.P. Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia, balanyuk@sio.rssi.ru, (3)VNIIGeosystem, Moscow, Russia, (4) Keldysh Institute of Applied Mathematics Russian Academy of Sciences, Moscow. The proposed crust waveguide model features versatility and enables to clarify the weakest elements in presently accepted visions of migration mechanisms and hydrocarbon fluid accumulations. The model of the crust waveguide is based on the following considerations. Horizontal tectonic stress is always present in the crust, causing shifts of layers relative to each other. When shear strains develop in a fractured layer, dilatant expansion occurs and is accompanied by increases in pore volume in the layer. This leads to pore pressure drops and suction of fluids into the expanding volume. In particular, those fluids are sucked which are present in the surface layers. They move through faulted and fractured zones downward, and reach the middle crust depths. This effect is basically known and is identified in geophysical literature as "tectonic pumping". At a certain moment, dilatant expansion is replaced by compression, and this process can be described by socalled compaction equations. Cyclic alteration of these regimes in the crust waveguide will finally ensure its dynamic equilibrium. The unbalanced processes in the middle crust leads to important geophysical implications. The crust waveguide located at 10 - 15 km depths acts as a pump. Water flows, which rush downward, are "washing up" the upper crust layers, dissolving and entraining mineral and organic materials. During the squeezing of fluids from the crust waveguide, these dissolved materials are concentrating and forming corresponding ore and hydrocarbon deposits in the upper
NASA Astrophysics Data System (ADS)
2014-02-01
On 5 - 6 June 2013, an extended session of the all-institute seminar was held at the Russian Federation State Scientific Center 'Alikhanov Institute for Theoretical and Experimental Physics' (ITEP). It was devoted to the 100th anniversary of the birth of Academician Isaak Yakovlevich Pomeranchuk, the founder of the Theory Department of ITEP. The announced agenda of the session on the ITEP website http://www.itep.ru/rus/Pomeranchuk100.html contained the following reports: (1) Gershtein S S (SRC 'Institute for High Energy Physics', Protvino, Moscow region) "I Ya Pomeranchuk and the large accelerator";(2) Keldysh L V (Lebedev Physical Institute, RAS (FIAN), Moscow) "Dynamic tunneling";(3) Vaks V G (National Research Centre 'Kurchatov Institute' (NRC KI), Moscow) "Brief reminiscences";(4) Smilga A V (Laboratoire Physique Subatomique et des technologies associées, Université de Nantes, France) "Vacuum structure in 3D supersymmetric gauge theories";(5) Khriplovich I B (Budker Institute of Nuclear Physics, SB RAS, Novosibirsk) "Gravitational four-fermion interaction and early Universe dynamics";(6) Dremin I M (FIAN, Moscow) "Elastic scattering of hadrons";(7) Belavin A A (Landau Institute of Theoretical Physics, RAS, Moscow) "Correlators in minimal string models";(8) Voloshin M B (Theoretical Physics Institute, University of Minnesota, USA) "Exotic quarkonium";(9) Nekrasov N A (Institut des hautes études scientifiques (IHES), France) "BPS/CFT correspondence";(10) Zarembo K (Uppsala Universitet, Sweden) "Exact results in supersymmetric theories and AdS/CFT correspondence";(11) Gorsky A S (ITEP, Moscow) "Baryon as a dyon instanton";(12) Blinnikov S I (ITEP, Moscow) "Mirror substance and other models for dark matter";(13) Rubakov V A (Institute for Nuclear Research, RAS, Moscow) "Test-tube Universe";(14) Kancheli O V (ITEP, Moscow) "50 years of reggistics";(15) Shevchenko V I (NRC KI) "In search of the chiral magnetic effect";(16) Kirilin V P (ITEP, Moscow) "Anomalies and
NASA Astrophysics Data System (ADS)
Mahfouzi, Farzad
ferromagnet (FM). I show that this could be due to the existence of Rashba spin-orbit coupling (SOC) at the interface of the FM and insulator. Assuming that the measured signals are quantum mechanical effect where a solution to the time dependent Schrodinger equation is required, I use Keldysh Green function formalism to introduce a "multi-photon" approach which takes into account the effects of time-dependent term exactly up to scatterings from a finite number of photons. We then proceed to find the corresponding Green function numerically using a recursive method which allows us to increase the size of the system significantly. We also implement other approximations such as adiabatic and rotating frame approaches and compared them with our approach. In Chapter 4, I investigate the spin and charge pumping from a precessing magnetization attached to the edge of a 2-dimensional topological insulator (2DTI). We show that, in this system a huge spin current (or voltage signal if the FM covers only one edge) can be pumped for very small cone angles of the precessing FM (proportional to the intensity of the applied microwave). In Chapter 5 I present the third project in this field of research, where, I investigated the pumping from FM attached to a 3-dimensional TI. Spin-transfer torque: Presented in Chapter 6, in this work I investigate the torque induced by a flow of spin-polarized current into a FM and check the condition in which it can cause the magnetization to flip. Motivated by recent experimental developments in the field, here I consider systems with strong SOC such as TIs within a magnetic tunnel junction (MTJ) heterostructure. In the theoretical part I show the correct way (as opposed to the conventional approach used in some theoretical works which suffers from violation of the gauge invariance) to calculate linear-response torque to the external applied voltage and for the numerical calculation I adopted a parallelized adaptive integration algorithm in order to take
Some Unknown Pages of the Living Organisms' First Orbital Flight
NASA Astrophysics Data System (ADS)
Malashenkov, D. C.
2002-01-01
The successful creation of ballistic rockets in USSR has allowed at the end of 1953 to make a real task of delivery of a payload into the Earth's orbit. In March 1954 during the meeting in the Academy of Sciences of USSR, the basic research problems conducted by means of artificial satellites of the Earth were determined. In May, 1954 S. Korolev has sent to Government of the USSR the report with the offer of creation the space satellites on the basis of intercontinental ballistic rocket -7 developed by him. It was the first time when the idea about possibility of interplanetary flights was stated in the official document. In August 1954 Council of Ministers of the USSR had ratified the submitted offers and have entrusted to work over scientific and theoretical problems of space flight. In the beginning of 1956 the Korolev's United Design Bureau was officially entrusted the creation and launch of undirected research satellite named "Object D" weighing 1.000-1.400 kg in 1957-1958. The main scientific management and development of scientific equipment was assigned to a commission of the Academy of Sciences of the USSR under the direction of . Keldysh. The measurement of parameters of the atmosphere, corpuscular radiation of the Sun, magnetic fields, space radiation etc. was planned during the "Object D" flight. The successful performance in the middle of 1956 of the second series of launches of geophysical rockets has allowed to gain a large volume of the information about parameters of physiological functions and behavior of animals in conditions of flight. For enlargement of these works the laboratory of V. Yazdovsky in the Institute of aviation medicine was extended to a department, the large group of the new employees, including V. Antipov, . Baevsky, I. Balakhovsky, B. Buylov, . Genin, O. Gazenko, A. Gurdjian, I. Kasyan, A. Kotovskaya, E..Yuganov, . Shepelev and others came to the department. But, owing to the delay of development of the scientific equipment for
Some Unknown Pages of the Living Organisms' First Orbital Flight
NASA Astrophysics Data System (ADS)
Malashenkov, D. C.
2002-01-01
The successful creation of ballistic rockets in USSR has allowed at the end of 1953 to make a real task of delivery of a payload into the Earth's orbit. In March 1954 during the meeting in the Academy of Sciences of USSR, the basic research problems conducted by means of artificial satellites of the Earth were determined. In May, 1954 S. Korolev has sent to Government of the USSR the report with the offer of creation the space satellites on the basis of intercontinental ballistic rocket -7 developed by him. It was the first time when the idea about possibility of interplanetary flights was stated in the official document. In August 1954 Council of Ministers of the USSR had ratified the submitted offers and have entrusted to work over scientific and theoretical problems of space flight. In the beginning of 1956 the Korolev's United Design Bureau was officially entrusted the creation and launch of undirected research satellite named "Object D" weighing 1.000-1.400 kg in 1957-1958. The main scientific management and development of scientific equipment was assigned to a commission of the Academy of Sciences of the USSR under the direction of . Keldysh. The measurement of parameters of the atmosphere, corpuscular radiation of the Sun, magnetic fields, space radiation etc. was planned during the "Object D" flight. The successful performance in the middle of 1956 of the second series of launches of geophysical rockets has allowed to gain a large volume of the information about parameters of physiological functions and behavior of animals in conditions of flight. For enlargement of these works the laboratory of V. Yazdovsky in the Institute of aviation medicine was extended to a department, the large group of the new employees, including V. Antipov, . Baevsky, I. Balakhovsky, B. Buylov, . Genin, O. Gazenko, A. Gurdjian, I. Kasyan, A. Kotovskaya, E..Yuganov, . Shepelev and others came to the department. But, owing to the delay of development of the scientific equipment for
INTRODUCTION: Surface Dynamics, Phonons, Adsorbate Vibrations and Diffusion
NASA Astrophysics Data System (ADS)
Bruch, L. W.
2004-07-01
components within the dilute nitrides. Electro-absorption and electro-refractive effects—Franz-Keldysh (FK) and quantum-confined Stark effect (QCSE) need to be studied theoretically in view of their importance for optical modulators. The aim of this special issue is to review the recent progress in theory, growth, characterization and device applications of dilute nitrides, and to collate what is known and what is not known in the field and address important fundamental physical properties and key material and device issues. The issue brings together a wide selection of papers from over 27 prominent research groups that have made key contributions to the field in the areas of research including growth, characterization and physical properties, devices and device integration, and theory and modelling. The editor is very grateful to all the invited authors for their contribution to this issue of Journal of Physics: Condensed Matter. I am grateful to Professors M J Adams, X Marie and Dr H Riechert for their help and contributions to the preparation of the editorial.
HISTORICAL MEMOIR: The play of light in crystals
NASA Astrophysics Data System (ADS)
Zakharchenya, Boris Petrovitch
2008-11-01
and experimentalists were taking part in the development of the concept of so-called polaritons in semiconductors, i.e. mixed states, when the 'mechanical' particle exciton mixes with the light wave. Pekar and Rashba of Kiev, Ginzburg and Agranovich of Moscow, Kaplyansky, Razbirin and Uraltsev of Leningrad, and also the above-mentioned American researchers, made the greatest contribution to the development of this sophisticated problem. Recalling the exciton physics of crystals of the 1950s and 1960s, I should call that time, after Schiller and Goethe, a period of Sturm und Drang. But even later on, the stormy waves of exciton spectroscopy did not calm down. There appeared lasers, which permitted Yaroslav Pokrovsky of the Institute of Electronics in Moscow to observe the hyperfine structure of exciton impurity complexes. The intense sources of light were also used for observation of the electron--hole condensate in semiconductors. But the initial idea of these investigations was stimulated by the existence of excitons: Bose particles and the attempt to observe their condensation. Veniamin Keldysh, Alexander Rogachev and a number of other Russian and foreign physicists contributed greatly to the solution of that problem. My friend, Carson Jeffries of Berkeley, a physicist and a painter, observed a gigantic (about a millimeter in size) electron--hole droplet in a crystal of germanium, and the results of his experiments were even mentioned in the New York Times. The 'exciton wave' rolled around the world, but its birthplace was Gross' small laboratory at the Physico-Technical Institute. It is most vexatious to read in a great many foreign textbooks on solid state physics that the Strasbourg professor S Nikitin was first to observe the exciton in cuprous oxide. That is not true at all! Nikitin bears no relation whatever to the discovery of the exciton. Gross first discovered a hydrogen-like series in a semiconductor in 1951 and published his findings in the Russian