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.