Unsuitability of the Keldysh parameter for laser fields
Reiss, H. R.
2010-08-15
The Keldysh parameter {gamma} is the accepted index for assessing field properties in laser-caused ionization. It is shown that {gamma} has significance only for the quasistatic electric (QSE) fields that underlie the tunneling model. The plane-wave (PW) fields produced by lasers are fundamentally different, with that difference becoming more emphatic as intensity increases. The gauge transformation that relates QSE and PW fields is valid only in a limited domain whose boundaries are not evident in a QSE context. The Keldysh {gamma} is shown to have no special meaning for laser-induced processes.
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.
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
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.
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.
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.
Hydrochemical characteristics of the waters in the western part of the Kara Sea
NASA Astrophysics Data System (ADS)
Makkaveev, P. N.; Melnikova, Z. G.; Polukhin, A. A.; Stepanova, S. V.; Khlebopashev, P. V.; Chultsova, A. L.
2015-07-01
Hydrochemical study in the Kara Sea was part of the program of the integrated expedition of the 59th cruise of the RV Akademik Mstislav Keldysh. Primary hydrochemical surveys were performed on the sections in the Yenisei Gulf, along the eastern and western branches of the St. Anna Trough, and across the Novozemel'skii Trough. Moreover, a flow-through system throughout, in which pH values of the surface waters were measured and samples for hydrochemical analyses were collected, was operated during vessel movement. A wide set of hydrochemical analyses was carried out, including tests for key nutrients (silicon and different forms of nitrogen and phosphorus), dissolved oxygen, and values of pH and total alkalinity. The report describes the hydrochemical conditions in the southwestern part of the Kara Sea. The basic results are presented and compared to those of the preceding integrated expeditions (49th cruise of the RV Dmitrii Mendeleev in 1993 and 54th cruise of the RV Akademik Mstislav Keldysh in 2007).
Generalized solutions to Protter problems for 3-D Keldysh type equations
NASA Astrophysics Data System (ADS)
Hristov, T.; Popivanov, N.; Schneider, M.
2014-12-01
Some three-dimensional boundary value problems for equations of Keldysh type are studied. Such type problems, but for equations of Tricomi type are stated by M. H. Protter [25] as 3-D analogues of Darboux or Cauchy-Goursat plane problems. It is well known that in contrast of well-posedness of 2D problems, the Protter problems are strongly ill-posed. In [12] Protter problem for Keldysh type equations is formulated and it is shown that it is not correctly set since the homogeneous adjoint problem has infinitely many nontrivial classical solutions. In the present paper a notion for generalized solution to Protter problem for Keldysh type equations is introduced. Further, results for existence and uniqueness of such solution are obtained.
Keldysh theory of strong field ionization: history, applications, difficulties and perspectives
NASA Astrophysics Data System (ADS)
Popruzhenko, S. V.
2014-10-01
The history and current status of the Keldysh theory of strong field ionization are reviewed. The focus is on the fundamentals of the theory, its most important applications and those aspects which still raise difficulties and remain under discussion. The Keldysh theory is compared with other nonperturbative analytic methods of strong field atomic physics and its important generalizations are discussed. Among the difficulties, the gauge invariance problem, the tunneling time concept, the conditions of applicability and the application of the theory to ionization of systems more complex than atoms, including molecules and dielectrics, are considered. Possible prospects for the future development of the theory are also discussed.
Comment on ``Multiphoton-ionization transition amplitudes and the Keldysh approximation''
NASA Astrophysics Data System (ADS)
Neto, H. S.; Davidovich, L.; Milonni, P. W.
1990-04-01
We show that the approach of Trombetta, Basile, and Ferrante [Phys. Rev. A 40, 2774 (1989)] does not establish the Keldysh ansatz as a well-defined approximation. In particular, it in effect replaces a vanishing contribution to the ionization rate by a nonvanishing one.
Comment on Multiphoton-ionization transition amplitudes and the Keldysh approximation''
Neto, H.S.A. ); Davidovich, L. ); Milonni, P.W. )
1990-04-01
We show that the approach of Trombetta, Basile, and Ferrante (Phys. Rev. A 40, 2774 (1989)) does not establish the Keldysh ansatz as a well-defined approximation. In particular, it in effect replaces a vanishing contribution to the ionization rate by a nonvanishing one.
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.
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.
NASA Astrophysics Data System (ADS)
Li, Yuan; Jalil, M. B. A.; Tan, Seng Ghee
2012-06-01
The conductance through a mesoscopic system of interacting electrons coupled to two adjacent leads is conventionally derived via the Keldysh nonequilibrium Green's function technique, in the limit of noninteracting leads [Y. Meir, N.S. Wingreen, Phys. Rev. Lett. 68 (1992) 2512]. We extend the standard formalism to cater for a quantum dot system with Coulombic interactions between the quantum dot and the leads. The general current expression is obtained by considering the equation of motion of the time-ordered Green's function of the system. The nonequilibrium effects of the interacting leads are then incorporated by determining the contour-ordered Green's function over the Keldysh loop and applying Langreth's theorem. The dot-lead interactions significantly increase the height of the Kondo peaks in density of states of the quantum dot. This translates into two Kondo peaks in the spin differential conductance when the magnitude of the spin bias equals that of the Zeeman splitting. There also exists a plateau in the charge differential conductance due to the combined effect of spin bias and the Zeeman splitting. The low-bias conductance plateau with sharp edges is also a characteristic of the Kondo effect. The conductance plateau disappears for the case of asymmetric dot-lead interaction.
[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
NASA Astrophysics Data System (ADS)
Dmitrenko, O. B.
2012-02-01
The nannofosssil assemblages have been analyzed in five cores taken from the Titanic area of the northwestern Atlantic (˜41°-42° N, ˜47°-50° W, water depths >3500 m) during cruises 41 and 43 of the R/V Akademik Mstislav Keldysh in 1998 and 2000. They correlate the host sediments with the upper Pleistocene-Holocene Emiliania huxleyi zone. The changes in the structure of the nannofossil assemblages and the lithological characteristics such as the content of biogenic CaCO3, the abundance of ice-rafted debris, and the grain-size composition were used for the high-resolution stratigraphy of sections with defining marine isotopic stages 1-3 of the last 24 kyr. A characteristic feature of the nannofossil assemblages from this area is their enrichment with the cold-resistant species Coccolthus pelagicus during the warm climatic stages and the lack of allochthonous coccolitophorid remains.
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.
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.
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.
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.
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.
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.
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)
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.
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)
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
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)
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
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
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
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…
Local bandgap control of germanium by silicon nitride stressor.
Kuroyanagi, R; Nguyen, L M; Tsuchizawa, T; Ishikawa, Y; Yamada, K; Wada, K
2013-07-29
We have proposed a new approach to tune the operation wavelength of Franz-Keldysh Ge electro-absorption modulation in Si photonics by controlling the local strain environment to cover the whole range of C + L bands (1.53 - 1.62 μm). The present paper shows a proof of strain-tuning modulator concept by the shift of the Ge absorption edge using SiN(x) stressor films and Franz-Keldysh effect in strain-controlled Ge.
Marunovic, Anja; Prokopec, Tomislav
2011-05-15
We calculate the one-loop graviton vacuum polarization induced by a massless, nonminimally coupled scalar field on Minkowski background. We make use of the Schwinger-Keldysh formalism, which allows us to study time dependent phenomena. As an application we compute the leading quantum correction to the Newtonian potential of a point particle. The novel aspect of the calculation is the use of the Schwinger-Keldysh formalism, within which we calculate the time transients induced by switching on the graviton-scalar coupling.
Utsumi, Yasuhiro; Golubev, Dmitri S; Schön, Gerd
2006-03-01
We evaluate the current distribution for a single-electron transistor with intermediate strength tunnel conductance. Using the Schwinger-Keldysh approach and the drone (Majorana) fermion representation, we account for the renormalization of system parameters. Nonequilibrium effects induce a lifetime broadening of the charge-state levels, which suppress large current fluctuations.
Dynamically assisted Sauter-Schwinger effect in inhomogeneous electric fields
NASA Astrophysics Data System (ADS)
Schneider, Christian; Schützhold, Ralf
2016-02-01
Via the world-line instanton method, we study electron-positron pair creation by a strong (but sub-critical) electric field of the profile E/ cosh2( kx) superimposed by a weaker pulse E ' / cosh2( ωt). If the temporal Keldysh parameter γ ω = mω/( qE) exceeds a threshold value γ ω crit which depends on the spatial Keldysh parameter γ k = mk/( qE), we find a drastic enhancement of the pair creation probability — reporting on what we believe to be the first analytic non-perturbative result for the interplay between temporal and spatial field dependences E( t, x) in the Sauter-Schwinger effect. Finally, we speculate whether an analogous effect (drastic enhancement of tunneling probability) could occur in other scenarios such as stimulated nuclear decay, for example.
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.
Matveev, O. P.; Shvaika, A. M.; Devereaux, T. P.; Freericks, J. K.
2015-12-08
Nonequilibrium dynamical mean-field theory (DMFT) is developed for the case of the charge-density-wave ordered phase. We consider the spinless Falicov-Kimball model which can be solved exactly. This strongly correlated system is then placed in an uniform external dc electric field. We present a complete derivation for nonequilibrium dynamical mean-field theory Green’s functions defined on the Keldysh-Schwinger time contour. We also discuss numerical issues involved in solving the coupled equations.
Electron energy relaxation in disordered graphene via e-phonon interaction
NASA Astrophysics Data System (ADS)
Chen, Wei; Clerk, Aashish
2012-02-01
Motivated by recent experiments, we study theoretically the energy relaxation of hot electrons in disordered graphene via electron-phonon interactions. In contrast to previous treatments [1], we explicitly treat the effects of electronic disorder. Using the Keldysh diagram technique, and including vertex corrections, we identify various mechanisms through which disorder can significantly change the magnitude and temperature dependence of the electronic energy relaxation rate. [1]Felix Von Oppen, Francisco Guinea, Eros Mariani, Phys. Rev.B 80, 075420 (2009)
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.
Oleĭnikova, G K; Shevchenko, L S; Kuznetsova, T A; Mikhaĭlov, V V
1995-02-01
Strain KMM 457 of Bacillus subtilis was isolated from a frozen sample of the soft coral Sarcophyton sp. The samples were collected in 1989 in the South China Sea near the Vietnam Shore during an expedition on the board of R/V "Akademik Oparin". Metabolites of the isolate were investigated and it was found to produce a number of physiologically active compounds. One of them designated as OGA showed fungicidal activity. By the physicochemical properties it was referred to the group of iturins. The comparison with the described antibiotics of the iturin group suggested that it was a new representative of the iturin group.
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
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.
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.
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
Bevan, Kirk H
2014-10-17
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.
Non-Fraunhofer interference pattern in inhomogeneous ferromagnetic Josephson junctions.
Alidoust, Mohammad; Sewell, Granville; Linder, Jacob
2012-01-20
Generic conditions are established for producing a non-Fraunhofer response of the critical supercurrent subject to an external magnetic field in ferromagnetic Josephson junctions. Employing the quasiclassical Keldysh-Usadel method, we demonstrate theoretically that an inhomogeneity in the magnitude of the energy scales in the system, including Thouless energy, exchange field and temperature gradient normal to the transport direction, influences drastically the standard Fraunhofer pattern. The exotic non-Fraunhofer response, similar to that observed in recent experiments, is described in terms of an intricate interplay between multiple "0-π" states and is related to the appearance of proximity vortices.
Strong-field S -matrix theory with final-state Coulomb interaction in all orders
NASA Astrophysics Data System (ADS)
Faisal, F. H. M.
2016-09-01
During the last several decades the so-called Keldysh-Faisal-Reiss or strong-field approximation (SFA) has been highly useful for the analysis of atomic and molecular processes in intense laser fields. However, it is well known that SFA does not account for the final-state Coulomb interaction which is, however, unavoidable for the ubiquitous ionization process. In this Rapid Communication we solve this long-standing problem and give a complete strong-field S -matrix expansion that accounts for the final-state Coulomb interaction in all orders, explicitly.
Transport theory beyond binary collisions
Carrington, Margaret E.; Mrowczynski, Stanislaw
2005-03-15
Using the Schwinger-Keldysh technique, we derive the transport equations for a system of quantum scalar fields. We first discuss the general structure of the equations and then their collision terms. Taking into account up to three-loop diagrams in {phi}{sup 3} model and up to four-loop diagrams in {phi}{sup 4} model, we obtain transport equations which include the contributions of multiparticle collisions and particle production processes, in addition to mean-field effects and binary interactions.
NASA Astrophysics Data System (ADS)
Kemper, A. F.; Sentef, M. A.; Moritz, B.; Freericks, J. K.; Devereaux, T. P.
2015-12-01
Using the nonequilibrium Keldysh formalism, we solve the equations of motion for electron-phonon superconductivity, including an ultrafast pump field. We present results for time-dependent photoemission spectra out of equilibrium which probe the dynamics of the superconducting gap edge. The partial melting of the order by the pump field leads to oscillations at twice the melted gap frequency, a hallmark of the Higgs or amplitude mode. Thus the Higgs mode can be directly excited through the nonlinear effects of an electromagnetic field and detected without requiring any additional symmetry breaking.
Pseudospin dynamics in multimode polaritonic Josephson junctions
NASA Astrophysics Data System (ADS)
Pavlovic, G.; Malpuech, G.; Shelykh, I. A.
2013-03-01
Using Keldysh-Green function formalism we theoretically analyzed the dynamics of multimode exciton-polariton Josephson junctions. We took into account the spinor nature of polaritons and considered in detail the role of coupling of the fundamental modes with excited states. We demonstrate that the coupling to the reservoir results in a change of the oscillation pattern. In particular, it can lead to renormalization of the oscillation frequency, appearance of higher order harmonics, and induce transition between the regimes of free Josephson oscillations and macroscopic quantum self-trapping.
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.
Measurement of the absolute cross section for multiphoton ionization of atomic hydrogen at 248 nm
Kyrala, G.A.; Nichols, T.D.
1990-01-01
We present measurements of the absolute rates for multiphoton ionization of the ground state from atomic hydrogen by a linearly polarized, subpicosecond KrF laser pulse at a wavelength of 248 nm. A laser crossed atomic beam technique is used. The irradiance was varied from 3{times}10{sup 12} w/cm{sup 2} to 2{times}10{sup 14} w/cm{sup 2} and three above threshold ionization peaks were observed. The measured rate for total electron production is less than predicted by the numerical and perturbation calculations, but significantly higher than calculated by the Reiss and Keldysh methods. 21 refs., 7 figs.
Temperature-controlled spin filter and spin valve based on Fe-doped monolayer MoS2.
Zou, Fei; Zhu, Lin; Gao, Gaoying; Wu, Menghao; Yao, Kailun
2016-02-17
The thermal transport properties of an iron-doped molybdenum disulfide system were explored theoretically using the density functional theory calculations combined with the Keldysh non-equilibrium Green's function approach. The results indicate that a perfect spin filtering effect and spin Seebeck effect are induced thermally. Excellently, there exists thermal colossal magnetoresistances, which exhibit a transition between positive and negative that can be tuned using temperature. These features were elucidated using the band structures of the electrodes and the transmission function together with current spectra. Our findings may be helpful in the design of highly efficient spin caloritronic devices.
Partition noise and statistics in the fractional quantum hall effect.
Safi, I; Devillard, P; Martin, T
2001-05-14
A microscopic theory of current partition in fractional quantum Hall liquids, described by chiral Luttinger liquids, is developed to compute the noise correlations, using the Keldysh technique. In this Hanbury-Brown and Twiss geometry, at Laughlin filling factors nu = 1/3, the real time noise correlator exhibits oscillations which persist over larger time scales than that of an uncorrelated Hall fluid. The zero frequency noise correlations are negative at filling factor 1/3 as for bare electrons (antibunching), but are strongly reduced in amplitude. These correlations become positive (bunching) for nu < or = 1/5, suggesting a tendency towards bosonic behavior.
Modeling of cavitation-bubble compression in benzene
NASA Astrophysics Data System (ADS)
Dnestrovskii, A. Yu.; Voropaev, S. A.; Zabrodina, E. A.
2016-08-01
In this study a two-dimensional model for calculating cavitation-bubble compression in benzene using a wide range of equations of state for ultrahigh pressures and temperatures is constructed. The calculations are carried out on the supercomputer of the Keldysh IAM. With the help of this model, the possibility of hits in the diamond-formation mode depending on the parameters of the external pressure and the initial bubble radius are analyzed. The dependence of the duration of the presence in the diamond-formation mode on these parameters is investigated.
Green's function of the magnetic topological insulator in a gradient expansion approach
NASA Astrophysics Data System (ADS)
Hama, Yusuke; Nagaosa, Naoto
2016-09-01
We study the Keldysh Green's function of the Weyl fermion surface state of the three-dimensional topological insulator coupled with a space-time dependent magnetization in the gradient expansion. Based on this, we analyze the electric charge and current densities as well as the energy density and current induced by spatially and temporally slowly varying magnetization fields. We show that all the above quantities except the energy current are generated by the emergent electromagnetic fields. The energy current emerges as the circular current reflecting the spatial modulation of an induced gap of the Weyl fermion.
Full Current Statistics in Diffusive Normal-Superconductor Structures
Belzig, W.; Nazarov, Yu. V.
2001-08-06
We study the current statistics in normal diffusive conductors in contact with a superconductor. Using an extension of the Keldysh Green's function method we are able to find the full distribution of charge transfers for all temperatures and voltages. For the non-Gaussian regime, we show that the equilibrium current fluctuations are enhanced by the presence of the superconductor. We predict an enhancement of the nonequilibrium current noise for temperatures below and voltages of the order of the Thouless energy E{sub Th}=D/L{sup 2} . Our calculation fully accounts for the proximity effect in the normal metal and agrees with experimental data.
NASA Astrophysics Data System (ADS)
Dzhioev, Alan A.; Kosov, D. S.
2012-01-01
We consider a single molecule circuit embedded into solvent. The Born dielectric solvation model is combined with Keldysh nonequilibrium Green's functions to describe the electron-transport properties of the system. Depending on the dielectric constant, the solvent induces multiple nonequilibrium steady states with corresponding hysteresis in molecular current-voltage characteristics as well as negative differential resistance. We identify the physical range of solvent and molecular parameters where the effects are present. The position of the negative differential resistance peak can be controlled by the dielectric constant of the solvent.
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.
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 .
Effective actions for anomalous hydrodynamics
NASA Astrophysics Data System (ADS)
Haehl, Felix M.; Loganayagam, R.; Rangamani, Mukund
2014-03-01
We argue that an effective field theory of local fluid elements captures the constraints on hydrodynamic transport stemming from the presence of quantum anomalies in the underlying microscopic theory. Focussing on global current anomalies for an arbitrary flavour group, we derive the anomalous constitutive relations in arbitrary even dimensions. We demonstrate that our results agree with the constraints on anomaly governed transport derived hitherto using a local version of the second law of thermodynamics. The construction crucially uses the anomaly inflow mechanism and involves a novel thermofield double construction. In particular, we show that the anomalous Ward identities necessitate non-trivial interaction between the two parts of the Schwinger-Keldysh contour.
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.
Dynamical Critical Phenomena in Driven-Dissipative Systems
NASA Astrophysics Data System (ADS)
Sieberer, L. M.; Huber, S. D.; Altman, E.; Diehl, S.
2013-05-01
We explore the nature of the Bose condensation transition in driven open quantum systems, such as exciton-polariton condensates. Using a functional renormalization group approach formulated in the Keldysh framework, we characterize the dynamical critical behavior that governs decoherence and an effective thermalization of the low frequency dynamics. We identify a critical exponent special to the driven system, showing that it defines a new dynamical universality class. Hence critical points in driven systems lie beyond the standard classification of equilibrium dynamical phase transitions. We show how the new critical exponent can be probed in experiments with driven cold atomic systems and exciton-polariton condensates.
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.
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.
Quantum theory of electroabsorption in semiconductor nanocrystals.
Tepliakov, Nikita V; Leonov, Mikhail Yu; Baranov, Alexander V; Fedorov, Anatoly V; Rukhlenko, Ivan D
2016-01-25
We develop a simple quantum-mechanical theory of interband absorption by semiconductor nanocrystals exposed to a dc electric field. The theory is based on the model of noninteracting electrons and holes in an infinitely deep quantum well and describes all the major features of electroabsorption, including the Stark effect, the Franz-Keldysh effect, and the field-induced spectral broadening. It is applicable to nanocrystals of different shapes and dimensions (quantum dots, nanorods, and nanoplatelets), and will prove useful in modeling and design of electrooptical devices based on ensembles of semiconductor nanocrystals.
Inherent contradictions in the tunneling-multiphoton dichotomy
Reiss, H. R.
2007-03-15
Strong-field phenomena are currently described as being multiphoton or tunneling, based on whether the Keldysh parameter {gamma} is greater than or less than unity. There are disqualifying features in this categorization. It is specific to the length gauge, dependent on only one intensity parameter, and backward in the sense that ionization with {gamma}>>1 can occur only by tunneling, and ionization with {gamma}<<1 must be over the barrier, and hence is not achieved by tunneling. As {gamma} becomes smaller, ionization becomes increasingly distant from tunneling, and eventually reaches conditions where the dipole approximation fails and there is no meaningful scalar-potential diagram at all.
Electronic transport in fullerene C20 bridge assisted by molecular vibrations.
Yamamoto, Takahiro; Watanabe, Kazuyuki; Watanabe, Satoshi
2005-08-01
The effect of molecular vibrations on electronic transport is investigated with the smallest fullerene C20 bridge, utilizing the Keldysh nonequilibrium Green's function techniques combined with the tight-binding molecular-dynamics method. Large discontinuous steps appear in the differential conductance when the applied bias voltage matches particular vibrational energies. The magnitude of the step is found to vary considerably with the vibrational mode and to depend on the local electronic states besides the strength of electron-vibration coupling. On the basis of this finding, a novel way to control the molecular motion by adjusting the gate voltage is proposed.
Zhang, Hao; Zhang, Guang-Ming; Yu, Lu
2009-04-15
A correct general formula for the spin current through an interacting quantum dot coupled to ferromagnetic leads with magnetization at an arbitrary angle θ is derived within the framework of the Keldysh formalism. Under asymmetric conditions, the spin current component J(z) may change sign for 0<θ<π. It is shown that the spin current and spin tunneling magnetoresistance exhibit different angle dependence in the free and Coulomb blockade regimes. In the latter case, the competition of the spin precession and the spin-valve effect could lead to an anomaly in the angle dependence of the spin current. PMID:21825366
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.
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.
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.
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.
Gas extraction and degradation of the submarine permafrost rocks on the Laptev Sea shelf
NASA Astrophysics Data System (ADS)
Lobkovskiy, L. I.; Nikiforov, S. L.; Dmitrevskiy, N. N.; Libina, N. V.; Semiletov, I. P.; Ananiev, R. A.; Meluzov, A. A.; Roslyakov, A. G.
2015-03-01
In 2011 and 2012, the interdisciplinary oceanic cruises of the R/V Akademik M.A. Lavrent'ev and R/V Viktor Buinitskii were conducted in the framework of the project of targeted basic research of the Russian Foundation for Basic Research. These studies identified strong methane jets because of the degradation of submarine permafrost rocks (SPRs), which is related to paleogeographical and modern factors of formation of the upper sedimentary sequence and also to structural peculiarities of the Arctic region. Large gas and water volumes are formed at the expense of the SPR defrosting; move along the upper sedimentary shelf sequence and along the surface of one or another layer (from coastal warmed areas to cooler deep areas); and form horizontally elongated convective cells, which activates destruction even at negative bottom temperatures. The methane emission will increase and become massive during the continuing SPR degradation.
NASA Astrophysics Data System (ADS)
Menzorova, N. I.; Rasskazov, V. A.
2009-12-01
A study of the state of the Russian coastal marine ecosystems of the Sea of Japan (the Tumen River mouth) and the Sea of Okhotsk (the eastern shelf of Sakhalin Island and the Sakhalin Gulf) and Kraternya Bight (Yankich Island, Kuril Islands) was carried out during the 29th expedition of the R/V Akademik Oparin. A highly sensitive express analysis using the DNase of the Strongylocentrotus intermedius sea urchin was utilized in order to evaluate the quality of the natural marine water of the areas experiencing different degrees of anthropogenic impact. The marine water quality was evaluated according to the degree of the DNase inhibition in the samples. The presence of ecological stress was shown at the aforementioned sites excluding Kraternya Bight. The method allows the fast (1 hour) analysis of the pollution of marine areas and, coupled with data on the hydrological, hydrochemical, and microbiological studies of water samples, provides the possibility to make an ecological forecast.
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.
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.
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.
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).
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.
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.
Out-of-equilibrium catalysis of chemical reactions by electronic tunnel currents.
Dzhioev, Alan A; Kosov, Daniel S; von Oppen, Felix
2013-04-01
We present an escape rate theory for current-induced chemical reactions. We use Keldysh nonequilibrium Green's functions to derive a Langevin equation for the reaction coordinate. Due to the out of equilibrium electronic degrees of freedom, the friction, noise, and effective temperature in the Langevin equation depend locally on the reaction coordinate. As an example, we consider the dissociation of diatomic molecules induced by the electronic current from a scanning tunnelling microscope tip. In the resonant tunnelling regime, the molecular dissociation involves two processes which are intricately interconnected: a modification of the potential energy barrier and heating of the molecule. The decrease of the molecular barrier (i.e., the current induced catalytic reduction of the barrier) accompanied by the appearance of the effective, reaction-coordinate-dependent temperature is an alternative mechanism for current-induced chemical reactions, which is distinctly different from the usual paradigm of pumping vibrational degrees of freedom.
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.
NASA Astrophysics Data System (ADS)
Val'kov, V. V.; Aksenov, S. V.; Ulanov, E. A.
2015-02-01
We present a solution for the problem of quantum electron transport through a magnetic atom adsorbed inside a break junction with paramagnetic metal electrodes. In agreement with experimental data, it was assumed that the conduction electrons experience inelastic scattering by the adsorbate due to s-d(f)-exchange interaction. The Keldysh technique was employed to obtain a general expression describing a current through the multilevel structure at finite temperatures in terms of the nonequilibrium Green's function. The use of the atomic representation allowed to exactly account for the non-equidistant structure of the energy spectrum of a magnetic atom and to simplify substantially the application of the Wick theorem for construction of the nonequilibrium diagrammatic technique for the Hubbard operators. The calculation of the current-voltage characteristics of the magnetic adatom in the tunnel regime at low temperatures revealed the presence of regions with a negative differential conductance in a magnetic field.
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
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).
Collective excitations of supersymmetric plasma
Czajka, Alina; Mrowczynski, Stanislaw
2011-02-15
Collective excitations of N=1 supersymmetric electromagnetic plasma are studied. Since the Keldysh-Schwinger approach is used, not only equilibrium but also nonequilibrium plasma, which is assumed to be ultrarelativistic, is under consideration. The dispersion equations of photon, photino, electron, and selectron modes are written down and the self-energies, which enter the equations, are computed in the hard loop approximation. The self-energies are discussed in the context of effective action which is also given. The photon modes and electron ones appear to be the same as in the usual ultrarelativistic plasma of electrons, positrons, and photons. The photino modes coincide with the electron ones and the selectron modes are as of a free relativistic massive particle.
On electrical phenomena in electroneutral superfluid systems
NASA Astrophysics Data System (ADS)
Shevchenko, S. I.; Rukin, A. S.
2010-02-01
Keldysh's theory of a rarefied superfluid electron-hole gas is extended to the case of possible pair polarization. It is established that the complex order parameter Φ(r1,r2), which is the wave function of a pair, satisfies a nonlinear, nonlocal, integrodifferential equation. The equation obtained is solved for the order parameter varying slowly over a distance of the order of the pair size. The dipole-moment density of the system is found from the known function Φ(r1,r2), and it is shown that the inhomogeneity of the system engenders a dipole moment proportional and oriented parallel to the gradient of the particle density. It is determined that an additional dipole moment associated with pair polarization due to the Lorentz force appears in a magnetic field.
Classical and quantum dissipation of bright solitons in a bosonic superfluid
NASA Astrophysics Data System (ADS)
Efimkin, Dmitry K.; Hofmann, Johannes B.; Galitski, Victor
We consider the quantum dissipation of a bright soliton in a quasi-one-dimensional bosonic superfluid. The dissipation appears due to interaction of the soliton with Bogoliubov excitations, which act as a bath for the soliton. Using a collective coordinate approach and the Keldysh formalism, we derive a Langevin equation for the soliton motion which contains both a friction and a stochastic force. We argue that due to the integrability of the original problem, Ohmic friction is absent, rendering the dynamics non-Markovian. We furthermore show that the resulting friction can be interpreted as the backreaction of Bogoliubov quasiparticles emitted by an accelerating soliton, which represents an analogue of the Abraham-Lorentz force known in electrodynamic.
Ho, Ching-Hwa; Lee, Jheng-Wei
2009-12-01
The band-edge property and built-in electric fields of two different Al(x)Ga(1-x)N/GaN(AlGaN/GaN) heterostructures (HSs) with and without an additional AlGaN inserted layer were studied by thermoreflectance (TR), photoluminescence (PL), and contactless electroreflectance (CER) techniques. The PL spectra characterize the band-edge luminescence property of GaN. Free exciton transitions of AlGaN and GaN were probed experimentally by TR. Prominent Franz-Keldysh oscillations (FKOs) of GaN and the opposite FKO phase of AlGaN were simultaneously detected by the additional AlGaN inserted sample with CER owing to the enhancement effect of built-in electric fields of GaN and AlGaN with the same polarity direction. Optoelectronics properties of the two HSs were characterized by the experimental analyses.
Effective action theory of Andreev level spectroscopy
NASA Astrophysics Data System (ADS)
Galaktionov, Artem V.; Zaikin, Andrei D.
2015-12-01
With the aid of the Keldysh effective action technique we develop a microscopic theory describing Andreev level spectroscopy experiments in nontunnel superconducting contacts. We derive an effective impedance of such contacts which accounts for the presence of Andreev levels in the system. At subgap bias voltages and low temperatures, inelastic Cooper pair tunneling is accompanied by transitions between these levels resulting in a set of sharp current peaks. We evaluate the intensities of such peaks, establish their dependence on the external magnetic flux piercing the structure and estimate the thermal broadening of these peaks. We also specifically address the effect of capacitance renormalization in a nontunnel superconducting contact and its impact on both the positions and heights of the current peaks. At overgap bias voltages, the I -V curve is determined by quasiparticle tunneling and contains current steps related to the presence of discrete Andreev states in our system.
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.
Continuous third harmonic generation in a terahertz driven modulated nanowire
NASA Astrophysics Data System (ADS)
Hamilton, Kathleen E.; Kovalev, Alexey A.; De, Amrit; Pryadko, Leonid P.
2015-06-01
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.
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.
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
Comprehensive analysis of the optical Kerr coefficient of graphene
Soh, Daniel B. S.; Hamerly, Ryan; Mabuchi, Hideo
2016-08-25
We present a comprehensive analysis of the nonlinear optical Kerr effect in graphene. We directly solve the S-matrix element to calculate the absorption rate, utilizing the Volkov-Keldysh-type crystal wave functions. We then convert to the nonlinear refractive index coefficients through the Kramers-Kronig relation. In this formalism, the source of Kerr nonlinearity is the interplay of optical fields that cooperatively drive the transition from valence to conduction band. This formalism makes it possible to identify and compute the rates of distinct nonlinear processes that contribute to the Kerr nonlinear refractive index coefficient. The four identified mechanisms are two-photon absorption, Raman transition,more » self-coupling, and quadratic ac Stark effect. As a result, we present a comparison of our theory with recent experimental and theoretical results.« less
Quantum dynamical field theory for nonequilibrium phase transitions in driven open systems
NASA Astrophysics Data System (ADS)
Marino, Jamir; Diehl, Sebastian
2016-08-01
We develop a quantum dynamical field theory for studying phase transitions in driven open systems coupled to Markovian noise, where nonlinear noise effects and fluctuations beyond semiclassical approximations influence the critical behavior. We systematically compare the diagrammatics, the properties of the renormalization group flow, and the structure of the fixed points of the quantum dynamical field theory and of its semiclassical counterpart, which is employed to characterize dynamical criticality in three-dimensional driven-dissipative condensates. As an application, we perform the Keldysh functional renormalization of a one-dimensional driven open Bose gas, where a tailored diffusion Markov noise realizes an analog of quantum criticality for driven-dissipative condensation. We find that the associated nonequilibrium quantum phase transition does not map into the critical behavior of its three-dimensional classical driven counterpart.
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.
Non-equilibrium Hybridization Expansion Impurity-solver
NASA Astrophysics Data System (ADS)
Dong, Qiaoyuan
2015-03-01
The study of non-equilibrium phenomena in strongly correlated systems has developed into one of the most active and exciting branches of condensed matter physics. Meanwhile, quantum impurity models play a prominent role as mathematical representations of quantum dots, single-molecule devices, and effective models for the dynamical mean field theory. We show results for a generalization of the hybridization expansion diagrammatic Monte Carlo technique for the Anderson impurity model. And we perform non-equilibrium calculations on the full Keldysh contour, where a dynamical sign problem vastly increases the complexity of real-time simulation. By further combining this method with a non-crossing approximation, our ``bold-line'' Monte Carlo can reach substantially longer times out of equilibrium than previously accessible, and provides an accurate description of quench and driven dynamics of correlated systems. Sponsored by the Department of Energy.
Electrostatic Spin Crossover in a Molecular Junction of a Single-Molecule Magnet Fe2
NASA Astrophysics Data System (ADS)
Hao, Hua; Zheng, Xiaohong; Song, Lingling; Wang, Ruining; Zeng, Zhi
2012-01-01
Spin crossover by means of an electric bias is investigated by spin-polarized density-functional theory calculations combined with the Keldysh nonequilibrium Green’s technique in a molecular junction, where an individual single-molecule magnet Fe2(acpybutO)(O2CMe)(NCS)2 is sandwiched between two infinite Au(100) nanoelectrodes. Our study demonstrates that the spin crossover, based on the Stark effect, is achieved in this molecular junction under an electric bias but not in the isolated molecule under external electric fields. The main reason is that the polarizability of the molecular junction has an opposite sign to that of the isolated molecule, and thus from the Stark effect the condition for the spin crossover in the molecular junction is contrary to that in the isolated molecule.
Comprehensive analysis of the optical Kerr coefficient of graphene
NASA Astrophysics Data System (ADS)
Soh, Daniel B. S.; Hamerly, Ryan; Mabuchi, Hideo
2016-08-01
We present a comprehensive analysis of the nonlinear optical Kerr effect in graphene. We directly solve the S -matrix element to calculate the absorption rate, utilizing the Volkov-Keldysh-type crystal wave functions. We then convert to the nonlinear refractive index coefficients through the Kramers-Kronig relation. In this formalism, the source of Kerr nonlinearity is the interplay of optical fields that cooperatively drive the transition from valence to conduction band. This formalism makes it possible to identify and compute the rates of distinct nonlinear processes that contribute to the Kerr nonlinear refractive index coefficient. The four identified mechanisms are two-photon absorption, Raman transition, self-coupling, and quadratic ac Stark effect. We also present a comparison of our theory with recent experimental and theoretical results.
Spin Transport in Multiply Connected Fractal Conductors
NASA Astrophysics Data System (ADS)
Lee, Bo-Ray; Chang, Ching-Ray; Klik, Ivo
2014-12-01
We consider spin and charge transport in a Sierpinski planar carpet; the interest here is its unique geometry. We analyze the fractal conductor as a combination of multiply connected quantum wires, and we observe the evolution of the transmission envelope in different fractal generations. For a fractal conductor dominated by resonant modes the transmission is characterized by strong fluctuations and conduction gaps. We show that charge and spin transport have different responses both to the presence of defects and to applied bias. At a high bias, or in a high-order fractal generation, spin accumulation is separated from charge accumulation because the larger drift velocity needs a longer polarization length, and the sample may turn into an insulator by the action of the defects. Our results are calculated numerically using the Keldysh Green function within the tight-binding framework.
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
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.
Monte Carlo Study of Real Time Dynamics on the Lattice
NASA Astrophysics Data System (ADS)
Alexandru, Andrei; Başar, Gökçe; Bedaque, Paulo F.; Vartak, Sohan; Warrington, Neill C.
2016-08-01
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.
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.
How Long Does it Take for a Non-Equilibrium System to Reach a Quasi-Thermal State?
NASA Astrophysics Data System (ADS)
Fotso, Herbert F.; Mikelsons, Karlis; Freericks, James K.
2013-03-01
We study the relaxation of an interacting system driven out of equilibrium by a constant electric field using Non-Equilibrium Dynamical Mean Field Theory. We use on the one hand a DMFT method which solves the steady state problem directly in frequency space, and on the other hand, a DMFT method that follows the transient time evolution of the system on the Keldysh contour. The system is described by the Falicov Kimball model which we follow across the metal - insulator transition. We find that the retarded Green's function quickly approaches that of the steady state while the lesser Green's function and, as a result the distribution function, slowly approach that of a steady state with an increased temperature due to the additional energy transferred to the system by the electric field. Analyses of this type can help understand the results of some experiments involving ultracold atomic gases.
Evolution of a Driven Quantum System Toward a Quasi-Thermal State
NASA Astrophysics Data System (ADS)
Fotso, Herbert; Mikelsons, Karlis; Freericks, James; Department of Physics, Georgetown Univeristy Team
2013-05-01
We study the relaxation of an interacting system driven out of equilibrium by a constant electric field using Non-Equilibrium Dynamical Mean Field Theory. We use on the one hand a DMFT method which solves the steady state problem directly in frequency space, and on the other hand, a DMFT method that follows the transient time evolution of the system on the Keldysh contour. The system is described by the Falicov Kimball model which we follow across the metal - insulator transition. We find that the retarded Green's function quickly approaches that of the steady state while the lesser Green's function and, as a result the distribution function, slowly approach that of a steady state with an increased temperature due to the additional energy transferred to the system by the electric field. Analyses of this type can help understand the results of some experiments involving ultracold atomic gases.
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.
Wave-packet analysis of strong-field ionization of sodium in the quasistatic regime*
NASA Astrophysics Data System (ADS)
Bunjac, Andrej; Popović, Duška B.; Simonović, Nenad S.
2016-05-01
Strong field ionization of the sodium atom in the tunnelling and over-the-barrier regimes is studied by examining the valence electron wave-packet dynamics in the static electric field. The lowest state energy and the ionization rate determined by this method for different strengths of the applied field agree well with the results obtained using other methods. The initial period of the nonstationary decay after switching the field on is analyzed and discussed. It is demonstrated that, if the Keldysh parameter is significantly lower than one (quasistatic regime), the probability of ionization by a laser pulse can be obtained from the static rates. Contribution to the Topical Issue "Advances in Positron and Electron Scattering", edited by Paulo Limao-Vieira, Gustavo Garcia, E. Krishnakumar, James Sullivan, Hajime Tanuma and Zoran Petrovic.
NASA Astrophysics Data System (ADS)
Greibe, Tine; Stenberg, Markku P. V.; Wilson, C. M.; Bauch, Thilo; Shumeiko, Vitaly S.; Delsing, Per
2011-03-01
In highly resistive superconducting tunnel junctions, excess subgap current is usually observed and is often attributed to microscopic pinholes in the tunnel barrier. We have studied the subgap current in superconductor-insulator-superconductor (SIS) and superconductor-insulator-normal-metal (SIN) junctions. In Al/AlOx/Al junctions, we observed a decrease of 2 orders of magnitude in the current upon the transition from the SIS to the SIN regime, where it then matched theory. In Al/AlOx/Cu junctions, we also observed generic features of coherent diffusive Andreev transport in a junction with a homogenous barrier. We use the quasiclassical Keldysh-Green function theory to quantify single- and two-particle tunneling and find good agreement with experiment over 2 orders of magnitude in transparency. We argue that our observations rule out pinholes as the origin of the excess current.
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.
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.
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.
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.
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
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.
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.
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
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.
Quantum-classical correspondence principles for locally nonequilibrium driven systems.
Smith, Eric
2008-02-01
Many of the core concepts and (especially field-theoretic) tools of statistical mechanics have developed within the context of thermodynamic equilibrium, where state variables are all taken to be charges, meaning that their values are inherently preserved under reversal of the direction of time. A principle concern of nonequilibrium statistical mechanics is to understand the emergence and stability of currents, quantities whose values change sign under time reversal. Whereas the correspondence between classical charge-valued state variables and their underlying statistical or quantum ensembles is quite well understood, the study of currents away from equilibrium has been more fragmentary, with classical descriptions relying on the asymmetric auxiliary-field formalism of Martin, Siggia, and Rose (and often restricted to the Markovian assumption of Doi and Peliti), while quantum descriptions employ a symmetric two-field formalism introduced by Schwinger and further clarified by Keldysh. In this paper we demonstrate that for quantum ensembles in which superposition is not violated by very strong conditions of decoherence, there is a large natural generalization of the principles and tools of equilibrium, which not only admits but requires the introduction of current-valued state variables. For these systems, not only do Martin-Siggia-Rose (MSR) and Schwinger-Keldysh (SK) field methods both exist, in some cases they provide inequivalent classical and quantum descriptions of identical ensembles. With these systems for examples, we can both study the correspondence between classical and quantum descriptions of currents, and also clarify the nature of the mapping between the structurally homologous but interpretationally different MSR and SK formalisms.
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.
Effective equilibrium theory of nonequilibrium quantum transport
Dutt, Prasenjit; Koch, Jens; Han, Jong; Le Hur, Karyn
2011-12-15
The theoretical description of strongly correlated quantum systems out of equilibrium presents several challenges and a number of open questions persist. Here, we focus on nonlinear electronic transport through an interacting quantum dot maintained at finite bias using a concept introduced by Hershfield [S. Hershfield, Phys. Rev. Lett. 70 2134 (1993)] whereby one can express such nonequilibrium quantum impurity models in terms of the system's Lippmann-Schwinger operators. These scattering operators allow one to reformulate the nonequilibrium problem as an effective equilibrium problem associated with a modified Hamiltonian. In this paper, we provide a pedagogical analysis of the core concepts of the effective equilibrium theory. First, we demonstrate the equivalence between observables computed using the Schwinger-Keldysh framework and the effective equilibrium approach, and relate Green's functions in the two theoretical frameworks. Second, we expound some applications of this method in the context of interacting quantum impurity models. We introduce a novel framework to treat effects of interactions perturbatively while capturing the entire dependence on the bias voltage. For the sake of concreteness, we employ the Anderson model as a prototype for this scheme. Working at the particle-hole symmetric point, we investigate the fate of the Abrikosov-Suhl resonance as a function of bias voltage and magnetic field. - Highlights: > Reformulation of steady-state nonequilibrium quantum transport, following Hershfield. > Derivation of effective equilibrium density operator using the 'open-system' approach. > Equivalence with the Keldysh description and formulas relating the two approaches. > Novel framework to treat interactions perturbatively. > Application to nonequilibrium Anderson model and fate of Abrikosov-Suhl resonance.
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.
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
Paleomagnetic data on the sedimentation rate near the Mendeleev Rise (Arctic Ocean)
NASA Astrophysics Data System (ADS)
Piskarev, A. L.; Andreeva, I. A.; Gus'kova, E. G.
2013-09-01
Seven cores of bottom sediments were collected during the cruise of R/V Akademik Fedorov in 2000 along the latitudinal profile crossing the Mendeleev Rise near 82° N, and then studied. The length of cores varies from 240 to 334 cm. In all cores, the boundary of the changing remanent magnetization vector corresponding to the Brunhes-Matuyama boundary was established reliably. In five cores, this boundary is at a depth of 86-102 cm; in two cores, collected to the west of the Mendeleev Rise, at depth levels of 188 and 208 cm. The correlation of paleomagnetic and lithological data demonstrates that the upper boundary of a bench of speckled pelites, overlapped by a bench of variegated pelites, is confined to the Olduvai episode or horizons lying slightly below. The average sedimentation rate of sediments from the Mendeleev Rise during the last 2-2.5 Ma have not exceeded 1-1.3 mm/ka, increasing towards the shelf seas of northeast Russia.
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.
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.
Multipoint observations of Ionospheric Alfvén Resonance
NASA Astrophysics Data System (ADS)
Baru, N. A.; Koloskov, A. V.; Yampolsky, Y. M.; Rakhmatulin, R. A.
2016-09-01
Among the processes that form properties of the geospace in the circumterrestrial plasma the electromagnetic resonances of the Earth, such as Schummann Resonance (SR) and Ionospheric Alfvén Resonance (IAR) are of great importance. IAR is more localized in space than SR and its properties largely depend on the characteristics of the propagation medium. In contrast to the SR, which has global nature and which is continuously observable at any time of the day, IAR signals are registered mostly during the nighttime and demonstrate more variability of the parameters than SR signals. At the Earth surface IAR is registered as Spectral Resonance Structure of the natural electromagnetic noise at frequency range 0.1-40 Hz. In this work we studied an influence of the environment characteristics on IAR parameters by the means of multipoint observations. Annual data series recorded at Ukrainian Antarctic Station "Akademik Vernadsky", Low Frequency Observatory of the Institute of Radio Astronomy near Kharkov (Ukraine) and magnetic station of Sayan Solar Observatory Mondy near Irkutsk (Russia) were used for the analysis. We investigated the behaviour of IAR parameters, such as probability of resonance lines registration and frequency spacing Δ F, for annual and diurnal intervals. These parameters were compared with characteristics of the ionosphere above all of the observation points and geomagnetic activity.
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.
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.
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.
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.
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.
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
Intense field electron excitation in transparent materials
NASA Astrophysics Data System (ADS)
Modoran, Georgia C.
The propagation of an intense laser through transparent materials can only be understood by considering a wide range of nonlinear effects and their simultaneous interaction. Electron plasma formation plays a crucial role and is the focus of this work. The mechanisms of the nonlinear ionization are not well understood. There are two proposed interactions that contribute to electron plasma formation: photoionization and avalanche ionization, but the individual contribution of each of these ionization processes is controversial. Keldysh theory has been proposed as a description of photoionization. Two models for avalanche ionization are used in the literature, but with different intensity dependence. We address and resolve these issues. In this thesis we present a spectrally resolved pump-probe experiment that directly measures the nonlinear ionization rates and plasma evolution in solid state media. Both pump and probe are derived from an 800 nm, 120 fs laser. The maximum ionization rates were obtained in sapphire (˜1.9x10 18 fs-1 ·cm-3), while in water (˜7.2x1017 fs-1 ·cm -3), fused silica (˜8.6x1017 fs -1 ·cm-3) and methanol (˜6.6x10 17 fs-1 ·cm-3) the ionization rates were slightly different. Our measured ionization rates are consistently larger that the theoretical rate given by Keldysh theory, suggesting that this theory does not correctly describe the photoionization process. We also present measurements that separate the two excitation processes and identify the role played by each in the ionization of media. The idea underneath these experiments is a very simple one: since the two ionization processes have different intensity dependence, the absorption of light in the medium should differ similarly. Therefore it should be possible to distinguish the two mechanisms by looking at the energy dependence of the absorption. From our result we find that avalanche and multiphoton ionization have varying relative contributions, depending on the band gap. For
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, and a more exact, numerical method of Y. Wang and K. F. Brennan. 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 formula, 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 (he 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 (he overlap integrals of the Bloch state which can only be
Quasi-Fermi level splitting and sub-bandgap absorptivity from semiconductor photoluminescence
NASA Astrophysics Data System (ADS)
Katahara, John K.; Hillhouse, Hugh W.
2014-11-01
A unified model for the direct gap absorption coefficient (band-edge and sub-bandgap) is developed that encompasses the functional forms of the Urbach, Thomas-Fermi, screened Thomas-Fermi, and Franz-Keldysh models of sub-bandgap absorption as specific cases. We combine this model of absorption with an occupation-corrected non-equilibrium Planck law for the spontaneous emission of photons to yield a model of photoluminescence (PL) with broad applicability to band-band photoluminescence from intrinsic, heavily doped, and strongly compensated semiconductors. The utility of the model is that it is amenable to full-spectrum fitting of absolute intensity PL data and yields: (1) the quasi-Fermi level splitting, (2) the local lattice temperature, (3) the direct bandgap, (4) the functional form of the sub-bandgap absorption, and (5) the energy broadening parameter (Urbach energy, magnitude of potential fluctuations, etc.). The accuracy of the model is demonstrated by fitting the room temperature PL spectrum of GaAs. It is then applied to Cu(In,Ga)(S,Se)2 (CIGSSe) and Cu2ZnSn(S,Se)4 (CZTSSe) to reveal the nature of their tail states. For GaAs, the model fit is excellent, and fitted parameters match literature values for the bandgap (1.42 eV), functional form of the sub-bandgap states (purely Urbach in nature), and energy broadening parameter (Urbach energy of 9.4 meV). For CIGSSe and CZTSSe, the model fits yield quasi-Fermi leveling splittings that match well with the open circuit voltages measured on devices made from the same materials and bandgaps that match well with those extracted from EQE measurements on the devices. The power of the exponential decay of the absorption coefficient into the bandgap is found to be in the range of 1.2 to 1.6, suggesting that tunneling in the presence of local electrostatic potential fluctuations is a dominant factor contributing to the sub-bandgap absorption by either purely electrostatic (screened Thomas-Fermi) or a photon
NASA Astrophysics Data System (ADS)
de Melo, Pedro Miguel M. C.; Marini, Andrea
2016-04-01
We present a full ab initio description of the coupled out-of-equilibrium dynamics of photons, phonons, and electrons. In the present approach, the quantized nature of the electromagnetic field as well as of the nuclear oscillations is fully taken into account. The result is a set of integrodifferential equations, written on the Keldysh contour, for the Green's functions of electrons, phonons, and photons where the different kinds of interactions are merged together. We then concentrate on the electronic dynamics in order to reduce the problem to a computationally feasible approach. By using the generalized Baym-Kadanoff ansatz and the completed collision approximation, we introduce a series of efficient but controllable approximations. In this way, we reduce all equations to a set of decoupled equations for the density matrix that describe all kinds of static and dynamical correlations. The final result is a coherent, general, and inclusive scheme to calculate several physical quantities: carrier dynamics, transient photoabsorption, and light emission, all of which include, at the same time, electron-electron, electron-phonon, and electron-photon interactions. We further discuss how all these observables can be easily calculated within the present scheme using a fully atomistic ab initio approach.
Unusually large spin polarization and magnetoresistance in a FeMg8-FeMg8 superatomic dimer.
Zhu, Lin; Qian, Meichun; Khanna, Shiv N
2013-08-14
Electronic transport across a FeMg8 magnetic superatom and its dimer has been investigated using a density functional theory combined with Keldysh nonequilibrium Green's-function formalism. For a single cluster, our studies for the cluster supported in various orientations on a Au(100) surface show that the transport is sensitive to the contact geometry. Investigations covering the cases where the axes of Mg square antiprism are 45°, perpendicular, and parallel to the transport direction, show that the equilibrium conductance, transferred charge, and current polarizations can all change significantly with orientation. Our studies on the transport across a magnetic superatom dimer FeMg8-FeMg8 focus on the effect of electrode contact distance and the support. The calculated I-V curves show negative differential resistance behavior at larger electrode-cluster contact distances. Further, the equilibrium conductance in ferromagnetic state shows an unusually high spin polarization that is about 81.48% for specific contact distance, and a large magnetoresistance ratio exceeding 500% is also found. The results show that the superatom assemblies can provide unusual transport characteristics, and that the spin polarization and magnetoresistance can be controlled via the contact geometry.
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).
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.
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.
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
Rottke, H.; Ludwig, J.; Sandner, W.
1996-09-01
We report multiphoton ionization experiments on H{sub 2} and D{sub 2} molecules at 1053- and 526.5-nm excitation wavelengths in the intensity range 5{times}10{sup 13}{endash}5{times}10{sup 14} W/cm{sup 2}. The intensity dependence of the total ion yield, the dissociation fraction, and the photoelectron spectrum is investigated. At 1053 nm we find a strong isotope effect in the dissociation fraction, whereas at 526.5 nm no such effect is observed. Up to 1{times}10{sup 14} W/cm{sup 2} the photoelectron spectrum at 526.5 nm is dominated by resonant ionization processes via Rydberg states of the molecules. They are shifted into resonance at intensities above {approximately}10{sup 13} W/cm{sup 2}. The spectra show that the potential energy curves of the resonant states must have a shape very similar to the corresponding ionic ones. They are therefore mainly determined by the dipole coupling between the ion core orbitals 1{ital s}{sigma}{sub {ital g}} and 2{ital p}{sigma}{sub {ital u}}. At 1053 nm two photoionization regimes are observed: the multiphoton regime with Keldysh parameter {gamma}{gt}1 showing resonance ionization structures, and the tunnel regime ({gamma}{lt}1) at high intensity. The isotope effect in the dissociation fraction at 1053 nm has no influence on the shape of the corresponding photoelectron spectra at this wavelength. {copyright} {ital 1996 The American Physical Society.}
NASA Astrophysics Data System (ADS)
Vinkler-Aviv, Yuval; Schiller, Avraham; Anders, Frithjof B.
2014-10-01
We develop a low-order conserving approximation for the interacting resonant-level model (IRLM), and apply it to (i) thermal equilibrium, (ii) nonequilibrium steady state, and (iii) nonequilibrium quench dynamics. Thermal equilibrium is first used to carefully gauge the quality of the approximation by comparing the results with other well-studied methods, and finding good agreement for small values of the interaction. We analytically show that the power-law exponent of the renormalized level width usually derived using renormalization group approaches can also be correctly obtained in our approach in the weak interaction limit. A closed expression for the nonequilibrium steady-state current is derived and analytically and numerically evaluated. We find a negative differential conductance at large voltages, and the exponent of the power-law suppression of the steady-state current is calculated analytically at zero temperature. The response of the system to quenches is investigated for a single lead as well as for two-lead setup at finite voltage bias at particle-hole symmetry using a self-consistent two-times Keldysh Green function approach, and results are presented for the time-dependent current for different bias and contact interaction strength.
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)).
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.
NASA Astrophysics Data System (ADS)
Tsuruta, Shuichi; Takeuchi, Hideo; Yamada, Hisashi; Hata, Masahiko; Nakayama, Masaaki
2013-04-01
We have investigated the characteristics of monochromatic terahertz electromagnetic waves emitted from coherent longitudinal optical (LO) phonons in undoped GaAs/n-type GaAs epitaxial structures with various thicknesses, which range from 200 nm to 1200 nm, of the undoped GaAs layer. The terahertz waves were measured at room temperature using an optical gating method with a photoconductive dipole antenna. It was found that the intensity of the terahertz waves markedly depends on the thickness of the undoped GaAs layer. The analysis of Franz-Keldysh oscillations observed with photoreflectance spectroscopy demonstrates that the built-in electric field strength in the undoped GaAs layer, which results from the Fermi-level pinning at the surface, increases from 6.1 kV/cm to 28.4 kV/cm with a decrease in the thickness. It was revealed that the amplitude of the terahertz wave is proportional to the electric field strength in the undoped GaAs layer. This fact indicates that the efficiency of the terahertz radiation is dominated by the initial polarization of the LO phonons induced by the built-in electric field, which provides us a simple strategy for the enhancement of the terahertz radiation from the coherent LO phonons.
Large electroabsorption susceptibility mediated by internal photoconductive gain in Ge nanowires.
Lee, Hyun-Seung; Kim, Cheol-Joo; Lee, Donghun; Lee, Ru Ri; Kang, Kibum; Hwang, Inchan; Jo, Moon-Ho
2012-11-14
Large spectral modulation in the photon-to-electron conversion near the absorption band-edge of a semiconductor by an applied electrical field can be a basis for efficient electro-optical modulators. This electro-absorption effect in Group IV semiconductors is, however, inherently weak, and this poses the technological challenges for their electro-photonic integration. Here we report unprecedentedly large electro-absorption susceptibility at the direct band-edge of intrinsic Ge nanowire (NW) photodetectors, which is strongly diameter-dependent. We provide evidence that the large spectral shift at the 1.55 μm wavelength, enhanced up to 20 times larger than Ge bulk crystals, is attributed to the internal Franz-Keldysh effect across the NW surface field of ~10(5) V/cm, mediated by the strong photoconductive gain. This classical size-effect operating at the nanometer scale is universal, regardless of the choice of materials, and thus suggests general implications for the monolithic integration of Group IV photonic circuits.
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.
Transport theory of massless fields
Mrowczynski, S. |
1997-08-01
Using the Schwinger-Keldysh technique we discuss how to derive the transport equations for the system of massless quantum fields. We analyze the scalar field models with quartic and cubic interaction terms. In the {phi}{sup 4} model the massive quasiparticles appear due to the self-interaction of massless bare fields. Therefore, the derivation of the transport equations strongly resembles one of the massive fields, but the subset of diagrams which provides the quasiparticle mass has to be resummed. The kinetic equation for the finite width quasiparticles is found, where, except for the mean-field and collision terms, there are terms which are absent in the standard Boltzmann equation. The structure of these terms is discussed. In the massless {phi}{sup 3} model the massive quasiparticles do not emerge and presumably there is no transport theory corresponding to this model. It is not surprising since the {phi}{sup 3} model is, in any case, ill defined. {copyright} {ital 1997} {ital The American Physical Society}
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)
Photon-assisted tunneling through a topological superconductor with Majorana bound states
Tang, Han-Zhao; Zhang, Ying-Tao; Liu, Jian-Jun
2015-12-15
Employing the Keldysh Nonequilibrium Green’s function method, we investigate time-dependent transport through a topological superconductor with Majorana bound states in the presence of a high frequency microwave field. It is found that Majorana bound states driven by photon-assisted tunneling can absorb(emit) photons and the resulting photon-assisted tunneling side band peaks can split the Majorana bound state that then appears at non-zero bias. This splitting breaks from the current opinion that Majorana bound states appear only at zero bias and thus provides a new experimental method for detecting Majorana bound states in the Non-zero-energy mode. We not only demonstrate that the photon-assisted tunneling side band peaks are due to Non-zero-energy Majorana bound states, but also that the height of the photon-assisted tunneling side band peaks is related to the intensity of the microwave field. It is further shown that the time-varying conductance induced by the Majorana bound states shows negative values for a certain period of time, which corresponds to a manifestation of the phase coherent time-varying behavior in mesoscopic systems.
Non-Markovian Quantum Friction of Bright Solitons in Superfluids
NASA Astrophysics Data System (ADS)
Efimkin, Dmitry K.; Hofmann, Johannes; Galitski, Victor
2016-06-01
We explore the quantum dynamics of a bright matter-wave soliton in a quasi-one-dimensional bosonic superfluid with attractive interactions. Specifically, we focus on the dissipative forces experienced by the soliton due to its interaction with Bogoliubov excitations. Using the collective coordinate approach and the Keldysh formalism, a Langevin equation of motion for the soliton is derived from first principles. The equation contains a stochastic Langevin force (associated with quantum noise) and a nonlocal in time dissipative force, which appears due to inelastic scattering of Bogoliubov quasiparticles off of the moving soliton. It is shown that Ohmic friction (i.e., a term proportional to the soliton's velocity) is absent in the integrable setup. However, the Markovian approximation gives rise to the Abraham-Lorentz force (i.e., a term proportional to the derivative of the soliton's acceleration), which is known from classical electrodynamics of a charged particle interacting with its own radiation. These Abraham-Lorentz equations famously contain a fundamental causality paradox, where the soliton (particle) interacts with excitations (radiation) originating from future events. We show, however, that the causality paradox is an artifact of the Markovian approximation, and our exact non-Markovian dissipative equations give rise to physical trajectories. We argue that the quantum friction discussed here should be observable in current quantum gas experiments.
Theoretical characterisation of point defects on a MoS2 monolayer by scanning tunnelling microscopy
NASA Astrophysics Data System (ADS)
González, C.; Biel, B.; Dappe, Y. J.
2016-03-01
Different S and Mo vacancies as well as their corresponding antisite defects in a free-standing MoS2 monolayer are analysed by means of scanning tunnelling microscopy (STM) simulations. Our theoretical methodology, based on the Keldysh nonequilibrium Green function formalism within the density functional theory (DFT) approach, is applied to simulate STM images for different voltages and tip heights. Combining the geometrical and electronic effects, all features of the different STM images can be explained, providing a valuable guide for future experiments. Our results confirm previous reports on S atom imaging, but also reveal a strong dependence on the applied bias for vacancies and antisite defects that include extra S atoms. By contrast, when additional Mo atoms cover the S vacancies, the MoS2 gap vanishes and a bias-independent bright protrusion is obtained in the STM image. Finally, we show that the inclusion of these point defects promotes the emergence of reactive dangling bonds that may act as efficient adsorption sites for external adsorbates.
NASA Astrophysics Data System (ADS)
Misawa, Tetsuro; Yokoyama, Takehito; Murakami, Shuichi
2012-02-01
Recent photoelectron spectroscopy experiments have revealed the presence of the Dirac cone on the surface of the topological insulator and its spin-splitting due to the spin-orbit interaction. In general, on spin-orbit coupled systems, electric fields induce spin polarizations as linear and nonlinear responses. Here we investigate the inverse Faraday effect on the surface of the topological insulator. The inverse Faraday effect is a non-linear optical effect where a circularly polarized light induces a dc spin polarization. We employ the Keldysh Green's function method to calculate the induced spin polarization and discuss its frequency dependence. In particular, in the low frequency limit, our analytical result gives the spin polarization proportional to the frequency and the square of the lifetime. As for the finite frequency regime, we employ numerical methods to discuss the resonance due to interband transitions. We also discuss the photogalvanic effect, where an illumination of a circular polarized light generates the dc charge current. Lastly, we evaluate those quantities with realistic parameters.[4pt] [1] T. Misawa, T. Yokoyama, S. Murakami, Phys. Rev. B84, 165407 (2011).
NASA Astrophysics Data System (ADS)
Janicki, Łukasz; Ramírez-López, Manolo; Misiewicz, Jan; Cywiński, Grzegorz; Boćkowski, Michał; Muzioł, Grzegorz; Chèze, Caroline; Sawicka, Marta; Skierbiszewski, Czesław; Kudrawiec, Robert
2016-05-01
Ga-polar, N-polar, and nonpolar m-plane GaN UN+ structures have been examined in air and vacuum ambient by contactless electroreflectance (CER). This technique is very sensitive to the surface electric field that varies with the Fermi level position at the surface. For UN+ GaN structures [i.e., GaN (undoped)/GaN (n-type)/substrate], a homogeneous built-in electric field is expected in the undoped GaN layer that is manifested by Franz-Keldysh oscillation (FKO) in CER spectra. A clear change in FKO has been observed in CER spectra for N-polar and nonpolar m-plane structures when changing from air to vacuum ambient. This means that those surfaces are very sensitive to ambient atmosphere. In contrast to that, only a small change in FKO can be seen in the Ga-polar structure. This clearly shows that the ambient sensitivity of the Fermi level position at the GaN surface varies with the crystallographic orientation and is very high for N-polar and nonpolar m-plane surfaces. This feature of the N-polar and nonpolar m-plane surfaces can be very important for GaN-based devices grown on these crystallographic orientations and can be utilized in some of the devices, e.g., sensors.
Magnetoelectrics in disordered topological insulator Josephson junctions
NASA Astrophysics Data System (ADS)
Bobkova, I. V.; Bobkov, A. M.; Zyuzin, Alexander A.; Alidoust, Mohammad
2016-10-01
We study theoretically the coupling of electric charge and spin polarization in an equilibrium and nonequilibrium electric transport across a two-dimensional Josephson configuration comprised of disordered surface channels of a three-dimensional topological insulator. In the equilibrium state of the system, we predict the Edelstein effect, which is much more pronounced than its counterpart in conventional spin-orbit coupled materials. Employing a quasiclassical Keldysh technique, we demonstrate that the ground state of the system can be shifted experimentally into arbitrary macroscopic superconducting phase differences other than the standard "0" or "π ," constituting a ϕ0 junction, solely by modulating a quasiparticle flow injection into the junction. We propose a feasible experiment in which the quasiparticles are injected into the topological insulator surface by means of a normal electrode and voltage gradient so that oppositely oriented stationary spin densities can be developed along the interfaces and allow for direct use of the spin-momentum locking nature of Dirac fermions in the surface channels. The ϕ0 state is proportional to the voltage difference applied between the injector electrode and superconducting terminals that calibrates the injection rate of particles and, therefore, the ϕ0 shift.
Kinetic theory for interacting Luttinger liquids
NASA Astrophysics Data System (ADS)
Buchhold, Michael; Diehl, Sebastian
2015-10-01
We derive a closed set of equations for the kinetics and non-equilibrium dynamics of interacting Luttinger Liquids with cubic resonant interactions. In the presence of these interactions, the Luttinger phonons become dressed but still well defined quasi-particles, characterized by a life-time much larger then the inverse energy. This enables the separation of forward time dynamics and relative time dynamics into slow and fast dynamics and justifies the so-called Wigner approximation, which can be seen as a "local-time approximation" for the relative dynamics. Applying field theoretical methods in the Keldysh framework, i.e. kinetic and Dyson-Schwinger equations, we derive a closed set of dynamic equations, describing the kinetics of normal and anomalous phonon densities, the phonon self-energy and vertex corrections for a Gaussian non-equilibrium initial state. In the limit of low phonon densities, the results from self-consistent Born approximation are recaptured, including Andreev's scaling solution for the quasi-particle life-time in a thermal state. As an application, we compute the relaxation of an excited state to its thermal equilibrium. While the intermediate time dynamics displays exponentially fast relaxation, the last stages of thermalization are governed by algebraic laws. This can be traced back to the importance of energy and momentum conservation at the longest times, which gives rise to dynamical slow modes.
Impact ionization in semiconductors and hot-carrier injection in Si-MOSFETs
Chen, Yuzhang.
1989-01-01
By incorporating non-parabolicity of energy band structure and energy-dependent impact ionization scattering rate into Keldysh's kinetic theory, an impact ionization model for electrons and holes in semiconductors is proposed. Numerically calculated impact ionization coefficients for Si, Ge, and GaAs in a wide range of electric fields and at different temperatures agree well with experimental data. The carrier energy distribution function numerically obtained from the model shows a distinct non-Maxwellian feature. The impact ionization model has been incorporated into a simulation model for substrate and gate currents in short n-channel Si-MOSFETs. Along with improvements in modeling of hot-carrier injection at the Si/SiO{sub 2} interface, the model successfully simulates and explains the experimentally observed second peak in the gate current versus gate voltage curve for very thin oxide devices and also the unusual behavior of the substrate and gate currents for lightly-doped-drain (LDD) devices which have not been simulated before. Based on the simulation results for LDD and related device structures, two new EPROM structures are proposed.
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.
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.
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.
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.
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
Li, Xin; Rong, Wenlong; Jiang, Lan; Zhang, Kaihu; Li, Cong; Cao, Qiang; Zhang, Guangming; Lu, Yongfeng
2014-12-01
We experimentally showed that the π/2-period oscillation of an ablation area with laser polarization direction can be observed in GaAs, ZnSe, MgO and LiF with cubic crystal by a femtosecond laser (800 nm, 100 fs) and that the modulation in the ablation area can be controlled by the laser fluence. While the polarization dependence is sustained in a wide range of laser fluences for a narrow band-gap crystal, it is strongly suppressed with a slight augmentation of laser fluence in a wide band-gap material. The polarization-dependent ablation is explained by the crystal's orientation-dependent reduced-electron mass and the resultant contrasting nonlinear absorptions with slightly different reduced electron mass. The interplay between photoionization and avalanche ionization is discussed to interpret the influence of laser fluence on polarization-dependent ablation. Based on Keldysh's theory, polarization-dependent ablation occurs in a mixed regime between tunneling and multiphoton ionization.
Non-Markovian Quantum Friction of Bright Solitons in Superfluids.
Efimkin, Dmitry K; Hofmann, Johannes; Galitski, Victor
2016-06-01
We explore the quantum dynamics of a bright matter-wave soliton in a quasi-one-dimensional bosonic superfluid with attractive interactions. Specifically, we focus on the dissipative forces experienced by the soliton due to its interaction with Bogoliubov excitations. Using the collective coordinate approach and the Keldysh formalism, a Langevin equation of motion for the soliton is derived from first principles. The equation contains a stochastic Langevin force (associated with quantum noise) and a nonlocal in time dissipative force, which appears due to inelastic scattering of Bogoliubov quasiparticles off of the moving soliton. It is shown that Ohmic friction (i.e., a term proportional to the soliton's velocity) is absent in the integrable setup. However, the Markovian approximation gives rise to the Abraham-Lorentz force (i.e., a term proportional to the derivative of the soliton's acceleration), which is known from classical electrodynamics of a charged particle interacting with its own radiation. These Abraham-Lorentz equations famously contain a fundamental causality paradox, where the soliton (particle) interacts with excitations (radiation) originating from future events. We show, however, that the causality paradox is an artifact of the Markovian approximation, and our exact non-Markovian dissipative equations give rise to physical trajectories. We argue that the quantum friction discussed here should be observable in current quantum gas experiments. PMID:27314722
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).
Pairing fluctuation ac conductivity of disordered thin films
NASA Astrophysics Data System (ADS)
Petković, Aleksandra; Vinokur, Valerii M.
2013-09-01
We study temperature T and frequency ω dependence of the in-plane fluctuation conductivity of a disordered superconducting film above the critical temperature. Our calculation is based on the nonlinear sigma model within the Keldysh technique. The fluctuation contributions of different physical origin are found and analyzed in a wide frequency range. In the low-frequency range, ω ≪ T, we reproduce the known leading terms and find additional subleading ones in the Aslamazov-Larkin and the Maki-Thompson contributions to the ac conductivity. We also calculate the density of states ac correction. In the dc case these contributions logarithmically depend on the Ginzburg-Landau rate and are considerably smaller that the leading ones. However, in the ac case an external finite-frequency electromagnetic field strongly suppresses the known Aslamazov-Larkin and Maki-Thompson ac contributions, while the corresponding new terms and the density of states contribution are weakly suppressed and therefore become relevant at finite frequencies.
NASA Astrophysics Data System (ADS)
Sato, S. A.; Yabana, K.; Shinohara, Y.; Otobe, T.; Lee, K.-M.; Bertsch, G. F.
2015-11-01
We calculate the energy deposition by very short laser pulses in SiO2 (α -quartz) with a view to establishing systematics for predicting damage and nanoparticle production. The theoretical framework is time-dependent density functional theory, implemented by the real-time method in a multiscale representation. For the most realistic simulations we employ a meta-GGA Kohn-Sham potential similar to that of Becke and Johnson. We find that the deposited energy in the medium can be accurately modeled as a function of the local electromagnetic pulse fluence. The energy-deposition function can in turn be quite well fitted to the strong-field Keldysh formula for a range of intensities from below the melting threshold to well beyond the ablation threshold. We find reasonable agreement between the damage threshold and the energy required to melt the substrate. Also, the depth of the ablated crater at higher energies is fairly well reproduced assuming that the material ablated with the energy exceeds that required to convert it to an atomic fluid. However, the calculated ablation threshold is higher than experiment, suggesting a nonthermal mechanism for the surface ablation.
Non-Markovian Quantum Friction of Bright Solitons in Superfluids.
Efimkin, Dmitry K; Hofmann, Johannes; Galitski, Victor
2016-06-01
We explore the quantum dynamics of a bright matter-wave soliton in a quasi-one-dimensional bosonic superfluid with attractive interactions. Specifically, we focus on the dissipative forces experienced by the soliton due to its interaction with Bogoliubov excitations. Using the collective coordinate approach and the Keldysh formalism, a Langevin equation of motion for the soliton is derived from first principles. The equation contains a stochastic Langevin force (associated with quantum noise) and a nonlocal in time dissipative force, which appears due to inelastic scattering of Bogoliubov quasiparticles off of the moving soliton. It is shown that Ohmic friction (i.e., a term proportional to the soliton's velocity) is absent in the integrable setup. However, the Markovian approximation gives rise to the Abraham-Lorentz force (i.e., a term proportional to the derivative of the soliton's acceleration), which is known from classical electrodynamics of a charged particle interacting with its own radiation. These Abraham-Lorentz equations famously contain a fundamental causality paradox, where the soliton (particle) interacts with excitations (radiation) originating from future events. We show, however, that the causality paradox is an artifact of the Markovian approximation, and our exact non-Markovian dissipative equations give rise to physical trajectories. We argue that the quantum friction discussed here should be observable in current quantum gas experiments.
Full counting statistics for the number of electrons in a quantum dot
NASA Astrophysics Data System (ADS)
Utsumi, Yasuhiro
2007-01-01
Motivated by recent real-time electron counting experiments, we evaluate the full counting statistics for the probability distribution of the electron number inside a quantum dot which is weakly coupled to source and drain leads. A non-Gaussian exponential distribution appears when there is no dot state close to the lead chemical potentials. We propose the measurement of the joint probability distribution of current and electron number, which reveals correlations between the two observables. We also show that for increasing strength of tunneling, the quantum fluctuations qualitatively change the probability distribution of the electron number. In this paper, we derive the cumulant generating functions (CGFs) of the joint probability distribution for several cases. The Keldysh generating functional approach is adopted to obtain the CGFs for the resonant-level model and for the single-electron transistor in the intermediate conductance regime. The general form for the CGF of the joint probability distribution is provided within the Markov approximation in an extension of the master equation approach [D. A. Bagrets and Yu. V. Nazarov, Phys. Rev. B 67, 085316 (2003)].
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.
Physics at the Moscow State University in 70-th. Photographs
NASA Astrophysics Data System (ADS)
Gaina, Alex B.
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.
Low-energy theory of transport in Majorana wire junctions
NASA Astrophysics Data System (ADS)
Zazunov, A.; Egger, R.; Levy Yeyati, A.
2016-07-01
We formulate and apply a low-energy transport theory for hybrid quantum devices containing junctions of topological superconductor (TS) wires and conventional normal (N) or superconducting (S) leads. We model TS wires as spinless p -wave superconductors and derive their boundary Keldysh Green's function, capturing both the Majorana end state and continuum quasiparticle excitations in a unified manner. We also specify this Green's function for a finite-length TS wire. Junctions connecting different parts of the device are described by the standard tunneling Hamiltonian. Using this Hamiltonian approach, one also has the option to include many-body interactions in a systematic manner. For N-TS junctions, we provide the current-voltage (I -V ) characteristics at arbitrary junction transparency and give exact results for the shot-noise power and the excess current. For TS-TS junctions, analytical results for the thermal noise spectrum and for the I -V curve in the high-transparency low-bias regime are presented. For S-TS junctions, we compute the entire I -V curve and clarify the conditions for having a finite Josephson current.
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.
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
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.
Nonequilibrium functional renormalization for driven-dissipative Bose-Einstein condensation
NASA Astrophysics Data System (ADS)
Sieberer, L. Â. M.; Huber, S. Â. D.; Altman, E.; Diehl, S.
2014-04-01
We present a comprehensive analysis of critical behavior in the driven-dissipative Bose condensation transition in three spatial dimensions. The starting point is a microscopic description of the system in terms of a many-body quantum master equation, where coherent and driven-dissipative dynamics occur on an equal footing. An equivalent Keldysh real-time functional integral reformulation opens up the problem to a practical evaluation using the tools of quantum field theory. In particular, we develop a functional renormalization group approach to quantitatively explore the universality class of this stationary nonequilibrium system. Key results comprise the emergence of an asymptotic thermalization of the distribution function, while manifest nonequilibrium properties are witnessed in the response properties in terms of a new, independent critical exponent. Thus, the driven-dissipative microscopic nature is seen to bear observable consequences on the largest length scales. The absence of two symmetries present in closed equilibrium systems—underlying particle number conservation and detailed balance, respectively—is identified as the root of this new nonequilibrium critical behavior. Our results are relevant for broad ranges of open quantum systems on the interface of quantum optics and many-body physics, from exciton-polariton condensates to cold atomic gases.
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.
Spin-controlled coexistence of 0 and π states in SFSFS Josephson junctions
NASA Astrophysics Data System (ADS)
Alidoust, Mohammad; Halterman, Klaus
2014-05-01
Using the Keldysh-Usadel formalism, we theoretically study the 0-π transition profiles and current-phase relations of magnetic SFSFS and SFSFFS Josephson nanojunctions in the diffusive regime. By allowing the magnetizations of the ferromagnetic layers to take arbitrary orientations, the strength and direction of the charge supercurrent flowing through the ferromagnetic regions can be controlled via the magnetization rotation in one of the ferromagnetic layers. Depending on the junction parameters, we find opposite current flow in the ferromagnetic layers, revealing that, remarkably, such configurations possess well-controlled 0 and π states simultaneously, creating a three-terminal 0-π spin switch. We demonstrate that the spin-controlled 0-π profiles trace back to the proximity induced odd-frequency superconducting correlations generated by the ferromagnetic layers. It is also shown that the spin-switching effect can be more pronounced in SFSFFS structures. The current-phase relations reveal the important role of the middle S electrode, where the spin-controlled supercurrent depends crucially on its thickness and phase differences with the outer S terminals.
NASA Astrophysics Data System (ADS)
Stenberg, Markku; Greibe, Tine; Wilson, Christopher; Bauch, Thilo; Shumeiko, Vitaly; Delsing, Per
2011-03-01
In highly resistive superconductor---insulator---superconductor (SIS) and superconductor---insulator---normal-metal (SIN) junctions, ``excess'' subgap current is usually observed. We have studied subgap conductance in Al/ Al Ox /Al and Al/ Al Ox /Cu tunnel junctions. In the former, we observed a huge (two orders of magnitude) decrease in subgap conductance upon the transition from the SIS to the SIN regime. In the latter, we observed several signatures of coherent diffusive two-particle transport. We use the quasiclassical Keldysh-Green function theory to quantify the contributions of the single- and two-particle processes on subgap conductance. Our observations indicate insignificance of highly transparent microscopic defects (``pinholes'') in the tunneling barrier, and we therefore argue that the common ``pinhole'' scenario is not the explanation for the observed excess subgap current in SIS tunnel junctions. This research was partly funded by the Office of the Director of National Intelligence (ODNI), Intelligence Advanced Research Projects Activity (IARPA), through the Army Research Office.
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.
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.
Large Tunable Thermophase in Superconductor – Quantum Dot – Superconductor Josephson Junctions
Kleeorin, Yaakov; Meir, Yigal; Giazotto, Francesco; Dubi, Yonatan
2016-01-01
In spite of extended efforts, detecting thermoelectric effects in superconductors has proven to be a challenging task, due to the inherent superconducting particle-hole symmetry. Here we present a theoretical study of an experimentally attainable Superconductor – Quantum Dot – Superconductor (SC-QD-SC) Josephson Junction. Using Keldysh Green’s functions we derive the exact thermo-phase and thermal response of the junction, and demonstrate that such a junction has highly tunable thermoelectric properties and a significant thermal response. The origin of these effects is the QD energy level placed between the SCs, which breaks particle-hole symmetry in a gradual manner, allowing, in the presence of a temperature gradient, for gate controlled appearance of a superconducting thermo-phase. This thermo-phase increases up to a maximal value of ±π/2 after which thermovoltage is expected to develop. Our calculations are performed in realistic parameter regimes, and we suggest an experimental setup which could be used to verify our predictions. PMID:27734919
Geometric-phase theory of coherent transport in insulators
NASA Astrophysics Data System (ADS)
Souza, Ivo; Íñiguez, Jorge; Vanderbilt, David
2003-03-01
We consider the macroscopic polarization current J=dP/dt induced, in the absence of scattering, by a homogeneous electric field l E(t) or some other time-varying parameter in the Hamiltonian of an insulating solid. We find that, even under nonadiabatic conditions, the integrated current Δ P=int_0^T J(t) dt is still given by the King-Smith-Vanderbilt geometric-phase formula,(R. D. King-Smith and D. Vanderbilt, Phys. Rev. B 47), 1651 (1993). originally derived assuming adiabaticity. This leads to a computationally convenient form for the time-dependent Schrödinger equation in an electric field. The recently proposed minimization of an energy functional for an insulator in a static field(I. Souza, J. Íñiguez, and D. Vanderbilt, Phys. Rev. Lett. 89), 117602 (2002). is recovered as a stationary solution. The formalism is used to compute the Franz-Keldysh effect in the context of a tight-binding model.
Ferromagnetic STM tip operating as a Spin-diode
NASA Astrophysics Data System (ADS)
Penteado, Poliana H.; Souza, Fabricio M.; Seridonio, Antônio C.; Coutinho, Renato M.; Vernek, Edson; Egues, J. Carlos
2011-03-01
We study spin-dependent transport in a system composed of a ferromagnetic STM tip coupled to an adsorbed atom (adatom) and to a host metallic (non-magnetic) surface. Electrons can tunnel directly from the tip to the surface or through the adatom. Our calculation is based on the nonequilibrium Green functions technique (Keldysh formalism). We self-consistently calculate the adatom spin occupation and its magnetization as a function of the tip position. We find that the adatom becomes magnetized when the tip approaches it; this magnetization switches sign as the voltage changes from forward to reverse bias. We also calculate the spin-resolved currents. If the tip is near the adatom, we obtain the spin-diode effect [PRB 75, 165303 (2007)] - i. e., unpolarized current for positive bias and polarized current for reverse bias - when the adatom is singly occupied. We also observe Friedel oscillations in the current as the tip-adatom distance increases [F. M. Souza, P. H. Penteado, et al. - to be submitted]. This work was supported by the funding agencies CNPq, CAPES, FAPEMIG and FAPESP.
Non-equilibrium STLS approach to transport properties of single impurity Anderson model
NASA Astrophysics Data System (ADS)
Rezai, Raheleh; Ebrahimi, Farshad
2014-04-01
In this work, using the non-equilibrium Keldysh formalism, we study the effects of the electron-electron interaction and the electron-spin correlation on the non-equilibrium Kondo effect and the transport properties of the symmetric single impurity Anderson model (SIAM) at zero temperature by generalizing the self-consistent method of Singwi, Tosi, Land, and Sjolander (STLS) for a single-band tight-binding model with Hubbard type interaction to out of equilibrium steady-states. We at first determine in a self-consistent manner the non-equilibrium spin correlation function, the effective Hubbard interaction, and the double-occupancy at the impurity site. Then, using the non-equilibrium STLS spin polarization function in the non-equilibrium formalism of the iterative perturbation theory (IPT) of Yosida and Yamada, and Horvatic and Zlatic, we compute the spectral density, the current-voltage characteristics and the differential conductance as functions of the applied bias and the strength of on-site Hubbard interaction. We compare our spectral densities at zero bias with the results of numerical renormalization group (NRG) and depict the effects of the electron-electron interaction and electron-spin correlation at the impurity site on the aforementioned properties by comparing our numerical result with the order U2 IPT. Finally, we show that the obtained numerical results on the differential conductance have a quadratic universal scaling behavior and the resulting Kondo temperature shows an exponential behavior.
High Response in a Tellurium-Supersaturated Silicon Photodiode
NASA Astrophysics Data System (ADS)
Wang, Xi-Yuan; Huang, Yong-Guang; Liu, De-Wei; Zhu, Xiao-Ning; Zhu, Hong-Liang
2013-03-01
Single crystalline silicon supersaturated with tellurium are formed by ion implantation followed by excimer nanosecond pulsed laser melting (PLM). The lattice damaged by ion implantation is restored during the PLM process, and dopants are effectively activated. The hyperdoped layer exhibits high and broad optical absorption from 400 to 2500nm. The n+ p photodiodes fabricated from these materials show high response (6.9A/W at 1000nm) with reverse bias 12 V at room temperature. The corresponding cut-off wavelength is 1258nm. The amount of gain and extended cut-off wavelength both increase with increasing reverse bias voltage; above 100% external quantum efficiency is observed even at a reverse bias of 1 V. The cut-off wavelength with 0 V bias is shorter than the commercial silicon detector. This implies that the Burstein-Moss shift is due to hyperdoping. The amount of the extended cut-off wavelength increases with increasing reverse bias voltage, suggesting existence of the Franz—Keldysh effect.
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.
Large Tunable Thermophase in Superconductor – Quantum Dot – Superconductor Josephson Junctions
NASA Astrophysics Data System (ADS)
Kleeorin, Yaakov; Meir, Yigal; Giazotto, Francesco; Dubi, Yonatan
2016-10-01
In spite of extended efforts, detecting thermoelectric effects in superconductors has proven to be a challenging task, due to the inherent superconducting particle-hole symmetry. Here we present a theoretical study of an experimentally attainable Superconductor – Quantum Dot – Superconductor (SC-QD-SC) Josephson Junction. Using Keldysh Green’s functions we derive the exact thermo-phase and thermal response of the junction, and demonstrate that such a junction has highly tunable thermoelectric properties and a significant thermal response. The origin of these effects is the QD energy level placed between the SCs, which breaks particle-hole symmetry in a gradual manner, allowing, in the presence of a temperature gradient, for gate controlled appearance of a superconducting thermo-phase. This thermo-phase increases up to a maximal value of ±π/2 after which thermovoltage is expected to develop. Our calculations are performed in realistic parameter regimes, and we suggest an experimental setup which could be used to verify our predictions.
Quantum optimal control theory in the linear response formalism
Castro, Alberto; Tokatly, I. V.
2011-09-15
Quantum optimal control theory (QOCT) aims at finding an external field that drives a quantum system in such a way that optimally achieves some predefined target. In practice, this normally means optimizing the value of some observable, a so-called merit function. In consequence, a key part of the theory is a set of equations, which provides the gradient of the merit function with respect to parameters that control the shape of the driving field. We show that these equations can be straightforwardly derived using the standard linear response theory, only requiring a minor generalization: the unperturbed Hamiltonian is allowed to be time dependent. As a result, the aforementioned gradients are identified with certain response functions. This identification leads to a natural reformulation of QOCT in terms of the Keldysh contour formalism of the quantum many-body theory. In particular, the gradients of the merit function can be calculated using the diagrammatic technique for nonequilibrium Green's functions, which should be helpful in the application of QOCT to computationally difficult many-electron problems.
Diagrammatic description of a system coupled strongly to a bosonic bath
NASA Astrophysics Data System (ADS)
Marthaler, Michael; Leppäkangas, Juha
2016-10-01
We study a system-bath description in the strong-coupling regime where it is not possible to derive a master equation for the reduced density matrix by a direct expansion in the system-bath coupling. A particular example is a bath with significant spectral weight at low frequencies. Through a unitary transformation, it can be possible to find a more suitable small expansion parameter. Within such an approach, we construct a formally exact expansion of the master equation on the Keldysh contour. We consider a system diagonally coupled to a bosonic bath and expansion in terms of a nondiagonal hopping term. The lowest-order expansion is equivalent to the so-called P (E ) theory or noninteracting blip approximation. The analysis of the higher-order contributions shows that there are two different classes of higher-order diagrams. We study how the convergence of this expansion depends on the form of the spectral function with significant weight at zero frequency.
NASA Astrophysics Data System (ADS)
Lu, Chien-Rong
The optical properties of the semimagnetic semiconducting alloy, Hg_{rm 1-x-y}Mn _{x}Cd _{y}Te, were studied by electrolyte electroreflectance (EER). The analysis of the experimental spectra was based on the theoretical lineshapes for the electroreflectance spectra in the low-field limit. The observed structures in the spectra include the E _0 and E_0 + Delta_0 transitions at the Gamma point and the E_1 and E_1 + Delta_1 transitions on the Lambda axis. The compositional variations of these transitions were compared with the predictions of the virtual crystal approximation. The physical mechanism of another type of electro -modulated spectroscopy, photoreflectance, was also investigated. The materials used in this investigation were GaAs thin films grown by molecular-beam-epitaxy (MBE). The nonuniformity of the internal modulation field in the space charge region was taken into account, for the first time, by a multilayer model. The lineshape calculated from the multilayer model provides a good fit to the experimental spectrum, and more importantly, it permits a measure of the correct transition energy from the spectrum. The temperature dependence of the periods of the Franz-Keldysh oscillations in the photoreflectance spectra indicates that the band bending near the surface decreases with decreasing 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.
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.
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.
Laser-assisted spin-polarized transport in graphene tunnel junctions.
Ding, Kai-He; Zhu, Zhen-Gang; Berakdar, Jamal
2012-07-01
The Keldysh nonequilibrium Green's function method is utilized to theoretically study spin-polarized transport through a graphene spin valve irradiated by a monochromatic laser field. It is found that the bias dependence of the differential conductance exhibits successive peaks corresponding to the resonant tunneling through the photon-assisted sidebands. The multi-photon processes originate from the combined effects of the radiation field and the graphene tunneling properties, and are shown to be substantially suppressed in a graphene spin valve which results in a decrease of the differential conductance for a high bias voltage. We also discuss the appearance of a dynamical gap around zero bias due to the radiation field. The gap width can be tuned by changing the radiation electric field strength and the frequency. This leads to a shift of the resonant peaks in the differential conductance. We also demonstrate numerically the dependences of the radiation and spin valve effects on the parameters of the external fields and those of the electrodes. We find that the combined effects of the radiation field, the graphene and the spin valve properties bring about an oscillatory behavior in the tunnel magnetoresistance, and this oscillatory amplitude can be changed by scanning the radiation field strength and/or the frequency. PMID:22677935
Effect of oxidation on interlayer exchange coupling in Fe|MgO|Fe tunnel junctions
NASA Astrophysics Data System (ADS)
Yang, H.-X.; Chshiev, M.; Kalitsov, A.; Schuhl, A.; Butler, W. H.
2010-03-01
The interlayer exchange coupling (IEC) in MgO-based magnetic tunnel junctions (MTJ) is a subject of major interest for spintronics community [1,2]. Recent experiments demonstrated that oxydation conditions strongly affect the character of the IEC in Fe/MgO/Fe(001) MTJs [3]. In order to elucidate the effect of over- and under-oxidation on the nature of the IEC in Fe|MgO|Fe MTJs, we performed systematic studies of the influence of O impurities and vacancies on the IEC using ab-initio and tight-binding approaches. We found that the O vacancies cause strong AF IEC in agreement with previous studies [2-4]. Furthermore, an additional O atom at the Fe|MgO interface makes the IEC ferromagnetic in for 3ML and above MgO thicknesses in agreement with experiment [3]. We demonstrate also that the full structural relaxation of ideal Fe|MgO|Fe MTJs may lead to the antiferromagnetic IEC. Tight-binding calculations of the IEC in the framework of the Keldysh formalism were also performed. The results obtained support our first principles calculations. [1] J. Faure-Vincent et al, Phys. Rev. Lett. 89, 107206 (2002); [2] T. Katayama et al., Appl. Phys. Lett. 89, 112503 (2006); [3] Y.F. Chiang et al, Phys. Rev. B 79, 184410 (2009); [4] M.Y. Zhuravlev et al, Phys. Rev. Lett. 94, 026806 (2005).
NASA Astrophysics Data System (ADS)
Kacimov, Anvar; Obnosov, Yurii; Al-Maktoumi, Ali; Al-Balushi, Mohammed
2011-11-01
Steady, Darcian, one-phase, phreatic surface flow of groundwater into a horizontal well with a pancake lens of light nonaqueous phase liquid (LNAPL) accumulated in the water table trough is studied by the method of complex analysis. A sharp interface model assumes groundwater capped by two isobaric limbs (groundwater-vadose zone interfaces) of a free surface with an in-between cambered segment of an immiscible LNAPL-water interface, along which pressure is hydrostatically increasing with the depth of the LNAPL "channel." The complex potential polygon is mapped onto an auxiliary half plane where the complex physical coordinate of the flow domain is represented in terms of singular integrals as a solution of the Keldysh-Sedov problem. The shapes of semi-infinite "wings" of the water table contacting the vadose zone gas and of a finite length LNAPL-groundwater interface are found from parametric equations that involve the sink strength and location with respect to the pancake surface, the ordinate of the lowest trough point, and the volume of LNAPL accreted in the lens. Critical conditions, corresponding to the lens contour cusping toward the sink, are found. The Riesenkampf solution contains a free parameter, which is fixed by specifying either a point on the free surface or the volume of the trough-intercepted LNAPL.
Theory of quantum transport in disordered systems driven by voltage pulse
NASA Astrophysics Data System (ADS)
Zhou, Chenyi; Chen, Xiaobin; Guo, Hong
2016-08-01
Predicting time-dependent quantum transport in the transient regime is important for understanding the intrinsic dynamic response of a nanodevice and for predicting the limit of how such a device can switch on or off a current. Theoretically, this problem becomes quite difficult to solve when the nanodevice contains disorder because the calculated transient current must be averaged over many disorder configurations. In this work, we present a theoretical formalism to calculate the configuration averaged time-dependent current flowing through a phase coherent device containing disorder sites where the transient current is driven by sharply turning on and off the external bias voltage. Our theory is based on the Keldysh nonequilibrium Green's function (NEGF) formalism and is applicable in the far from equilibrium nonlinear response quantum transport regime. The effects of disorder scattering are dealt with by the coherent potential approximation (CPA) extended in the time domain. We show that after approximations such as CPA and vertex corrections for calculating the multiple impurity scattering in the transient regime, the derived NEGFs perfectly satisfy a Ward identity. The theory is quantitatively verified by comparing its predictions to the exact solution for a tight-binding model of a disordered two-probe transport junction.
NASA Astrophysics Data System (ADS)
Komatsu, Kensuke; Tachibana, Yoshihiro; Alexeev, Vladimir
2016-04-01
In summer 2013, we conducted 6 hourly radiosonde observation between off-ice and on-ice by Russian icebreaker "Akademik Fedorov" passing through the marginal ice-zone in Laptev Sea during NABOS project (Nansen and Amundsen Basins Obsevational System). During observation period, the warmer and humid air mass was advected by southeasterly wind from Siberia to Laptev sea because the low-pressure system was passing The temperature profiles bellow 600 m was maintaining the cold pool associated with a sea ice and the inversion layer formed above it. The humidity profiles were, however, not trapped until the height of inversion layer, they reached at higher levels (< 5000 m). These observational evidences implied that the humid air from Siberia was lifted on the cold pool maintained by sea ice and this process could transport the moisture to upper level in the arctic region. To verify these processes and examine the impact of the existence of sea ice, we conducted the numerical experiment by WRF. Three boundary conditions were adopted to simulation; present sea ice, removed all sea ice, and increased sea ice area. As primary results, the trajectories of air parcel from Siberia was rising to upper level with released the latent heat due to the condensation of humid air. The case of present sea ice transported much moisture vertically in the arctic region than other two cases. More detail results will be reported on the day. The process of the vertical moisture lifting due to the cold pool could contribute to the heat transport from the mid-latitude surface to the upper level in the arctic.
The Australasian Antarctic Expedition 2013-2014: Practicing 'Citizen-Science' in a Changing World
NASA Astrophysics Data System (ADS)
Fogwill, C. J.; Turney, C. S.
2014-12-01
Government funding is the cornerstone of modern science. But with declining investment in science across most of the Western World, a major challenge for society is where best to place what little resource we have. Which research questions should have the greatest priority? Nowhere are these issues more pressing than in the Antarctic, where bases have and continue to play host to 'big-science', multi-year programmes of research, locking up logistical support and costs. But in a warming world, the areas with the greatest effects of climate change aren't always near government research stations. With this in mind, in 2012 a plan was formed to visit Commonwealth Bay, a remote area off the East Antarctic Ice Sheet, where in 2010, an iceberg the size of Rhode Island, known as B09B, dramatically knocked a 60-mile long tongue of ice off the Mertz Glacier into the Southern Ocean, setting off a cascade of change. Inspired by the expeditions of the past, we advertised berths for sale to take citizen scientists south with us, harnessing their interest, experience and investment. People responded far and wide. We were oversubscribed, and the Australasian Antarctic Expedition 2013-2014 was born. With the Russian-owned MV Akademik Shokalskiy as the expedition vessel, we set out south from the New Zealand port of Bluff in late November 2013. During our journey south and on the ice we undertook a number of scientific firsts for the region actively engaging the volunteer scientists on board in projects ranging from oceanography, biology, ecology, geology and glaciaology. The expedition demostrated how private funding could support targeted programmes of research and communicate it to the wider world. Small-science research can capture the public's imagination and also reap real scientific outputs. Although it is a funding model developed in the Antarctic a hundred years ago, the beauty is it can applied anywhere in the world.
Seamounts Identified By High-Resolution Imagery Offshore Kenya
NASA Astrophysics Data System (ADS)
Henderson, J. F.; Kagasi, J.; Gikuhi, M.; Njuguna, S.
2008-12-01
Multibeam bathymetry and 2-D seismic reflection surveys were carried out between 2007 and 2008 by the Government of Kenya for the purpose of delineating Kenya's extended continental shelf beyond the 200 nautical mile boundary, as allowed under Article 76 of the United Nations Convention on the Law of the Sea (UNCLOS). The unique dataset acquired includes areas surveyed for the first time and provides new information on the geological processes of the continental shelf, slope and abyssal plain along the Kenyan passive margin. High-resolution multibeam bathymetry of almost the entire Kenyan continental slope was acquired using two multibeam systems (Kongsberg Simrad EM120 and EM710) aboard the M/V L'Espoir in November/December 2007. A multi-channel seismic survey followed in April/May 2008 (R/V Akademik Alexander Karpinsky) and provided high-resolution seismic reflection profiles. During these surveys, three features interpreted to be seamounts were discovered along Kenya's continental slope at water depths between 2750 and 3500 m. The size of the features varies from 2.5 to 10 km in diameter and 570 to 1740 m in height. The Davie Fracture Zone, a north-south trending transform fault was also identified in the seismic reflection profiles. The ridge, possibly extending from 26°S off south Madagascar to as far north as 2°S, is thought to have been created by the separation and direction of motion of Madagascar from Africa that began in the middle Jurassic. The discovery of these features and the integration of both multibeam bathymetry and seismic reflection profiles provides new information in the study of seamount distribution and their relationship to nearby transform faults.
NASA Astrophysics Data System (ADS)
Zadorozhny, A. M.; Kikhtenko, V. N.; Kokin, G. A.; Tuchkov, G. A.; Tyutin, A. A.; Chizhov, A. F.; Shtirkov, O. V.
1994-10-01
The results of rocket measurements of ozone and nitric oxide concentrations, vertical component of the electric field strength, positive ion density, and temperature of the middle atmosphere during the extremely strong solar proton events (SPE) of October 1989 are presented. The measurements were taken in the southern hemisphere in the Indian Ocean (40 deg - 60 deg S and 45 deg - 75 deg E) on board the research vessel Akademik Shirshov. A great increase in ion densities above approximately 30 km and nitric oxide concentrations above approximately 40 km with maximum (NO) approximately 2 x 10(exp 9)/cu cm at approximately 45- to 55-km heights were observed during the SPE. A decrease in ozone concentrations above approximately 35 km with the maximum decrease of about 20-25% at approximately 50-km height and cooling of the atmosphere at approximately 40- to 60-km heights with the maximum temperature decrease of about 14 deg near 50 km were also observed. An unexpectedly large value of the vertical electric field strength of 12 V/m was detected in the lower mesosphere at about 58 km at 58 deg 30 min S during the SPE. The obtained results on ozone, nitric oxide, ion concentration, and temperature qualitatively agree with the existing photochemical concepts on the impact of solar proton events on the middle atmosphere, while the measured cooling of the stratopause is greater than that predicted by theoretical models. The increase of the vertical electric field strength observed during the SPE points out a very high electrical activity of the mesosphere and unknown generation mechanisms of electrical phenomena in the middle atmosphere.
NASA Astrophysics Data System (ADS)
Brandt, A.; Elsner, N.; Brenke, N.; Golovan, O.; Malyutina, M. V.; Riehl, T.; Schwabe, E.; Würzberg, L.
2013-02-01
Faunistic data from a newly designed camera-epibenthic sledge (C-EBS) are presented. These were collected during the joint Russian-German expedition SoJaBio (Sea of Japan Biodiversity Studies) on board the R.V. Akademik Lavrentyev from four transects (A-D) between 460 and 3660 m depth. In total, 244,531 macro- and megafaunal individuals were sampled with the classes Malacostraca (80,851 individuals), Polychaeta (36,253 ind.) and Ophiuroidea (34,004 ind.) being most abundant. Within the Malacostraca, Peracarida (75,716 ind.) were most abundant and within these, the Isopoda were the dominant taxon (27,931 ind.), followed by Amphipoda (21,403 ind.), Cumacea (13,971 ind.) and Tanaidacea (10,830 ind.). Mysidacea (1581 ind.) were least frequent. Bivalvia, Amphipoda, Cumacea and Mysidacea as well as inbenthic meiofaunal Nematoda occurred in higher numbers at the shallower stations and their numbers decreased with increasing depth. Polychaeta, Isopoda, and Tanaidacea, on the contrary, increased in abundance with increasing depth. Only one isopod species was sampled at abyssal depths in the Sea of Japan but at very high abundance: Eurycope spinifrons Gurjanova, 1933 (Asellota: Munnopsidae). Echinoderms occurred frequently at the shallower slope stations. Ophiuroids were dominating, followed by holothurians, and echinoids and asteroids which occurred in lower numbers and primarily at the shallower stations of transects A and B. Only 2163 individual anthozoans were recorded and these were mostly confined to the lower slope. The technical design of a new C-EBS is described. Next to temperature-insulated epi- and suprabenthic samplers, it is equipped with still and video cameras, which deliver information on seabed topography and megafaunal occurrence. Furthermore, Aanderaa CTD and SEAGUARD RCM allow for collection of physical parameters, such as near bottom oxygen composition, temperature and conductivity.
NASA Astrophysics Data System (ADS)
Lizunov, G.; Yampolski, Yu.; Korepanov, V.; Lytvynenko, L.; Zalizovsky, A.
The impact of meteorological processes upon the ionosphere cannot be ignored in conceptual space weather models. The giant energy stored in motion of tropospheric air masses (weather fronts, cyclones, stream jets, penetrating convection, etc) serves as a powerful source of upward energy fluxes propagating from the lower to upper atmosphere. The prospective energy carrier might be associated with the middle-scale atmospheric gravity waves (AGW) traveling upwards to the ionospheric heights and producing the effects known as traveling ionospheric disturbances (TID's). We present the results of detailed experimental and theoretical study of these phenomena. The original data had been provided by experiments in the region of high meteorological activity, namely Antarctic coast of the Drake Passage, where the Ukrainian Antarctic station " Akademik Vernadsky" is located (UK's "Michael Faraday" till 1996). The permanent data sets were collected over the seven years from 1996 till 2002. The passing atmospheric fronts were in most cases accompanied by excitation of middle-scale AGW's and quasiperiodic variations of magnetic field components, showing the same time periods as the atmospheric pressure. As follows from the cross-correlation analysis of the magnetic field and pressure variations, the magnetic field normally lagged behind the pressure by few tens minutes. On this base we elaborate a quantitative model describing the AGW excitation by weather fronts, AGW propagation to the upper atmosphere and generation of geomagnetic pulsation in the ionospheric dynamo-region. We expect to carry out further experiments onboard Ukrainian remote sensing satellite "Sich-1M" (launch in 2004), which payload contains optical and radar equipment allowing to detect weather systems as well as a set of electromagnetic sensors ("Variant" experiment" for registration of the fine structure of fields and currents in the ionosphere. We are going to compare a ground based meteorological and
Quasi-Fermi level splitting and sub-bandgap absorptivity from semiconductor photoluminescence
Katahara, John K.; Hillhouse, Hugh W.
2014-11-07
A unified model for the direct gap absorption coefficient (band-edge and sub-bandgap) is developed that encompasses the functional forms of the Urbach, Thomas-Fermi, screened Thomas-Fermi, and Franz-Keldysh models of sub-bandgap absorption as specific cases. We combine this model of absorption with an occupation-corrected non-equilibrium Planck law for the spontaneous emission of photons to yield a model of photoluminescence (PL) with broad applicability to band-band photoluminescence from intrinsic, heavily doped, and strongly compensated semiconductors. The utility of the model is that it is amenable to full-spectrum fitting of absolute intensity PL data and yields: (1) the quasi-Fermi level splitting, (2) the local lattice temperature, (3) the direct bandgap, (4) the functional form of the sub-bandgap absorption, and (5) the energy broadening parameter (Urbach energy, magnitude of potential fluctuations, etc.). The accuracy of the model is demonstrated by fitting the room temperature PL spectrum of GaAs. It is then applied to Cu(In,Ga)(S,Se){sub 2} (CIGSSe) and Cu{sub 2}ZnSn(S,Se){sub 4} (CZTSSe) to reveal the nature of their tail states. For GaAs, the model fit is excellent, and fitted parameters match literature values for the bandgap (1.42 eV), functional form of the sub-bandgap states (purely Urbach in nature), and energy broadening parameter (Urbach energy of 9.4 meV). For CIGSSe and CZTSSe, the model fits yield quasi-Fermi leveling splittings that match well with the open circuit voltages measured on devices made from the same materials and bandgaps that match well with those extracted from EQE measurements on the devices. The power of the exponential decay of the absorption coefficient into the bandgap is found to be in the range of 1.2 to 1.6, suggesting that tunneling in the presence of local electrostatic potential fluctuations is a dominant factor contributing to the sub-bandgap absorption by either purely electrostatic (screened Thomas-Fermi) or
NASA Astrophysics Data System (ADS)
Lange, C.; Schubert, O.; Hohenleutner, M.; Langer, F.; Baierl, S.; Maag, T.; Urbanek, B.; Edwards, E. R. J.; Woltersdorf, G.; Bougeard, D.; Huttner, U.; Golde, D.; Meier, T.; Kira, M.; Koch, S. W.; Huber, R.
2015-02-01
Ultrafast transport of electrons in semiconductors lies at the heart of high-speed electronics, electro-optics and fundamental solid-state physics. Intense phase-locked terahertz (THz) pulses at photon energies far below electronic interband resonances may serve as a precisely adjustable alternating bias, strongly exceeding d.c. breakdown voltages. Here, we exploit the near-field enhancement in gold metamaterial structures on undoped bulk GaAs, driven by few-cycle THz transients centered at 1 THz, to bias the semiconductor substrate with field amplitudes exceeding 12 MV/cm. Such fields correspond to a potential drop of the bandgap energy over a distance of only two unit cells. In this extremely off-resonant scenario characterized by a Keldysh parameter of γK ≈ 0.02, massive interband Zener tunneling injects a sizeable carrier density exceeding 1019 cm-3, and strong photoluminescence results. At a center frequency of 30 THz, THz transients with peak fields of 72 MV/cm analogously excite carriers in a bulk, semiconducting GaSe crystal, without metamaterial. Here, in contrast, we are able to drive coherent interband polarization and furthermore dynamical Bloch oscillations of electrons in the conduction band, on femtosecond time scales. The dynamics entail the generation of absolutely phase-stable high-harmonic transients containing spectral components up to the 22nd order of the fundamental frequency, spanning 12.7 optical octaves throughout the entire terahertz-to-visible domain between 0.1 and 675 THz. Our experiments establish a new field of light-wave electronics exploring coherent charge transport at optical clock rates and bring picosecond-scale electric circuitry at the interface of THz optics and electronics into reach.
Evidence for broken Galilean invariance at the quantum spin Hall edge
NASA Astrophysics Data System (ADS)
Geissler, Florian; Crépin, François; Trauzettel, Björn
2015-12-01
We study transport properties of the helical edge channels of a quantum spin Hall insulator, in the presence of electron-electron interactions and weak, local Rashba spin-orbit coupling. The combination of the two allows for inelastic backscattering that does not break time-reversal symmetry, resulting in interaction-dependent power-law corrections to the conductance. Here, we use a nonequilibrium Keldysh formalism to describe the situation of a long, one-dimensional edge channel coupled to external reservoirs, where the applied bias is the leading energy scale. By calculating explicitly the corrections to the conductance up to fourth order of the impurity strength, we analyze correlated single- and two-particle backscattering processes on a microscopic level. Interestingly, we show that the modeling of the leads together with the breaking of Galilean invariance has important effects on the transport properties. Such breaking occurs because the Galilean invariance of the bulk spectrum transforms into an emergent Lorentz invariance of the edge spectrum. With this broken Galilean invariance at the quantum spin Hall edge, we find a contribution to single-particle backscattering with a very low power scaling, while in the presence of Galilean invariance the leading contribution will be due to correlated two-particle backscattering only. This difference is further reflected in the different values of the Fano factor of the shot noise, an experimentally observable quantity. The described behavior is specific to the Rashba scatterer and does not occur in the case of backscattering off a time-reversal-breaking, magnetic impurity.
Theoretical description of nonequilibrium behavior in charge density wave systems
NASA Astrophysics Data System (ADS)
Shen, Wen
The fast development of time resolved photoemission (TRPES) techniques allow us to discover the rich features of nonequilibrium phenomena which may not appear in equilibrium. One of the most explored topics is the nonequilibrium behavior of a charge density wave (CDW) material. Being an ordered phase at low temperature, the CDW state provides a fertile ground to study electron-electron and electron-ion interactions. By driving this material out of equilibrium and taking ultrafast time resolution snapshots of its behavior, TRPES helps us understand these interactions and sheds light on the mechanisms behind these and other complex material properties, such as metal-insulator transitions, high temperature superconductivity, and magnetic phenomena. Recent experiments on TRPES in CDW materials show an ultrafast CDW gap closure in systems such as 1T--TaS2 and TbTe3 and the subsequent separation of time scales for the electron-electron interaction and the electron-lattice interaction. But it is still not clear what happens during the ultrashort period (in first 100 femtosecond). In this dissertation, we solve a two band model describing this ultrafast process in a CDW system. By fixing the lattice distortion effect in the CDW, we studied the nonequilibrium excitations of the electrons under a strong electric field. This research is performed by calculating nonequilibrium Green's functions (NGF) along the Kadanoff-Baym-Keldysh contour. We solved this nonequilibrium problem exactly. We show non-perturbative results and explore the nonlinear electronic behavior under an ultrashort light pulses. In addition to the TRPES problem, we also examined the behavior of Bloch oscillations under a large DC field, the response to an AC electric field, high harmonic generation from solids, and the crossover between frequency-driven excitation and amplitude-driven excitation.
Wavelength dependence of femtosecond laser-induced damage threshold of optical materials
Gallais, L. Douti, D.-B.; Commandré, M.; Batavičiūtė, G.; Pupka, E.; Ščiuka, M.; Smalakys, L.; Sirutkaitis, V.; Melninkaitis, A.
2015-06-14
An experimental and numerical study of the laser-induced damage of the surface of optical material in the femtosecond regime is presented. The objective of this work is to investigate the different processes involved as a function of the ratio of photon to bandgap energies and compare the results to models based on nonlinear ionization processes. Experimentally, the laser-induced damage threshold of optical materials has been studied in a range of wavelengths from 1030 nm (1.2 eV) to 310 nm (4 eV) with pulse durations of 100 fs with the use of an optical parametric amplifier system. Semi-conductors and dielectrics materials, in bulk or thin film forms, in a range of bandgap from 1 to 10 eV have been tested in order to investigate the scaling of the femtosecond laser damage threshold with the bandgap and photon energy. A model based on the Keldysh photo-ionization theory and the description of impact ionization by a multiple-rate-equation system is used to explain the dependence of laser-breakdown with the photon energy. The calculated damage fluence threshold is found to be consistent with experimental results. From these results, the relative importance of the ionization processes can be derived depending on material properties and irradiation conditions. Moreover, the observed damage morphologies can be described within the framework of the model by taking into account the dynamics of energy deposition with one dimensional propagation simulations in the excited material and thermodynamical considerations.
Electron gas induced in SrTiO3
NASA Astrophysics Data System (ADS)
Fu, Han; Reich, K. V.; Shklovskii, B. I.
2016-03-01
This mini-review is dedicated to the 85th birthday of Prof. L.V. Keldysh, from whom we have learned so much. In this paper, we study the potential and electron density depth profiles in surface accumulation layers in crystals with a large and nonlinear dielectric response such as SrTiO3 (STO) in the cases of planar, spherical, and cylindrical geometries. The electron gas can be created by applying an induction D 0 to the STO surface. We describe the lattice dielectric response of STO using the Landau-Ginzburg free energy expansion and employ the Thomas-Fermi (TF) approximation for the electron gas. For the planar geometry, we arrive at the electron density profile n( x) ∝ ( x + d)-12/7, where d ∝ D 0 -12/7 . We extend our results to overlapping electron gases in GTO/STO/GTO heterojunctions and electron gases created by spill-out from NSTO (heavily n-type doped STO) layers into STO. Generalization of our approach to a spherical donor cluster creating a big TF atom with electrons in STO brings us to the problem of supercharged nuclei. It is known that for an atom with a nuclear charge Ze where Z > 170, electrons collapse onto the nucleus, resulting in a net charge Zn < Z. Here, instead of relativistic physics, the collapse is caused by the nonlinear dielectric response. Electrons collapse into the charged spherical donor cluster with radius R when its total charge number Z exceeds the critical value Z c ≈ R/ a, where a is the lattice constant. The net charge e Z n grows with Z until Z exceeds Z* ≈ ( R/ a)9/7. After this point, the charge number of the compact core Z n remains ≈ Z*, with the rest Z* electrons forming a sparse TF atom with it. We extend our studies of collapse to the case of long cylindrical clusters as well.
Applications of many-body physics to relativistic heavy ion collisions
NASA Astrophysics Data System (ADS)
Fillion-Gourdeau, Francois
In this dissertation, many-body physics techniques are used to study and improve ideas related to the description of heavy ion collisions at very high energy. The first part of the thesis concerns the production of tensor mesons in proton-proton (pp) collisions. An effective theory where the f2 meson couples to the energy-momentum tensor is proposed and a comparison of the inclusive cross-section computed in the collinear factorization, the k⊥-factorization and the color glass condensate is performed. A study of the phenomenology in pp collisions then shows a strong dependence on the parametrization of the unintegrated distribution function. The conclusion is that f2 meson production can be utilized to improve the understanding of the proton wave-function. In the second part, a similar investigation is performed by analysing the production cross-section of the eta' meson in pp and proton-nucleus (pA) collisions. The nucleus and proton are described by the CGC and the k⊥ -factorization respectively. A new technique for the computation of Wilson lines---color charge densities correlators in the McLerran-Venugopalan model is developped. The phenomenology shows that the cross-section in pA collisions is very sensitive to the value of the saturation scale, a crucial ingredient of the CGC picture. In the third part of the thesis, the collision term of the Boltzmann equation is derived from first principles at all orders and for any number of participating particles, starting from the full out-of-equilibrium quantum field theory and using the multiple scattering expansion. Finally, the emission of photons from a non-abelian strong classical field is investigated. A formalism based on Schwinger-Keldysh propagators relating the production rate of photons to the retarded solution of the Dirac equation in a background field is presented.
Many-body theory of electrical, thermal and optical response of molecular heterojunctions
NASA Astrophysics Data System (ADS)
Bergfield, Justin Phillip
In this work, we develop a many-body theory of electronic transport through single molecule junctions based on nonequilibrium Green's functions (NEGFs). The central quantity of this theory is the Coulomb self-energy matrix of the junction SigmaC. SigmaC is evaluated exactly in the sequential-tunneling limit, and the correction due to finite lead-molecule tunneling is evaluated using a conserving approximation based on diagrammatic perturbation theory on the Keldysh contour. In this way, tunneling processes are included to infinite order, meaning that any approximation utilized is a truncation in the physical processes considered rather than in the order of those processes. Our theory reproduces the key features of both the Coulomb blockade and coherent transport regimes simultaneously in a single unified theory. Nonperturbative effects of intramolecular correlations are included, which are necessary to accurately describe the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap, essential for a quantitative theory of transport. This work covers four major topics related to transport in single-molecule junctions. First, we use our many-body theory to calculate the nonlinear electrical response of the archetypal Au-1,4-benzenedithiol-Au junction and find irregularly shaped 'molecular diamonds' which have been experimentally observed in some larger molecules but which are inaccessible to existing theoretical approaches. Next, we extend our theory to include heat transport and develop an exact expression for the heat current in an interacting nanostructure. Using this result, we discover that quantum coherence can strongly enhance the thermoelectric response of a device, a result with a number of technological applications. We then develop the formalism to include multi-orbital lead-molecule contacts and multi-channel leads, both of which strongly affect the observable transport. Lastly, we include a dynamic screening correction to
Nonequilibrium dynamical mean-field theory
NASA Astrophysics Data System (ADS)
Freericks, James
2007-03-01
Dynamical mean-field theory (DMFT) is establishing itself as one of the most powerful approaches to the quantum many-body problem in strongly correlated electron materials. Recently, the formalism has been generalized to study nonequilibrium problems [1,2], such as the evolution of Bloch oscillations in a material that changes from a diffusive metal to a Mott insulator [2,3]. Using a real-time formalism on the Kadanoff-Baym-Keldysh contour, the DMFT algorithm can be generalized to the case of systems that are not time-translation invariant. The computational algorithm has a parallel implementation with essentially a linear scale up when running on thousands of processors. Results on the decay of Bloch oscillations, their change of character within the Mott insulator, and movies on how electrons redistribute themselves due to their response to an external electrical field will be presented. In addition to solid-state applications, this work also applies to the behavior of mixtures of light and heavy cold atoms in optical lattices. [1] V. M. Turkowski and J. K. Freericks, Spectral moment sum rules for strongly correlated electrons in time-dependent electric fields, Phys. Rev. B 075108 (2006); Erratum, Phys. Rev. B 73, 209902(E) (2006). [2] J. K. Freericks, V. M. Turkowski , and V. Zlati'c, Nonlinear response of strongly correlated materials to large electric fields, in Proceedings of the HPCMP Users Group Conference 2006, Denver, CO, June 26--29, 2006 edited by D. E. Post (IEEE Computer Society, Los Alamitos, CA, 2006), to appear. [3] J. K. Freericks, V. M. Turkowski, and V. Zlati'c, Nonequilibrium dynamical mean-field theory, submitted to Phys. Rev. Lett. cond-mat//0607053.
Earthquake Monitoring at 9° 50'N on the East Pacific Rise RIDGE 2000 Integrated Studies Site
NASA Astrophysics Data System (ADS)
Tolstoy, M.; Waldhauser, F.; Kim, W.
2004-12-01
In the fall of 2003 nine ocean bottom seismometers (OBSs) were deployed from the R/V Keldysh within the `bull's-eye' region of the R2K ISS at 9° 49'N - 9° 51'N on the East Pacific Rise as part of the Ridge 2000 Integrated Studies Site. These instruments were recovered using the R/V Atlantis in April 2004, and twelve more were deployed to take their place for a second year of monitoring (with three years total planned). During the turn-around cruise, two short temporary deployments (~4-8 days), of an additional 3 OBSs each, were accomplished to provide very dense instrument spacing (a few 100 m) around specific vents where in situ chemical monitoring was taking place (Luther et al.). Good data were collected on seven of the nine long deployment and six short deployment OBSs. We will present early results from analysis of these data including an estimate of the level of activity observed through-out the seven month period of the first deployment, and preliminary epicenters. Data will also be shown from the short temporary deployments. Early analysis of these data indicates an event rate of ~8 events per day for events where arrivals are apparent on at least three instruments, and may therefore expect to be located. Also notable in these data are pulses and prolonged periods of what appear to be tremor. This tremor is not generally coherent or synchronous from station to station and is therefore likely a very localized phenomena associated with hydrothermal fluid flow. The exceptionally well characterized and monitored seafloor at this site will allow for unprecedented correlation of observed seismic activity with local biology, geology, geochemical and hydrothermal monitoring. In addition, past and future detailed geophysical imaging of this area will provide an excellent context for observed faulting and fracturing.
Introduction to Atomic Dynamics in Intense Light Fields
NASA Astrophysics Data System (ADS)
Faisal, Farhad H. M.
A brief description is given of the early developments leading to the discovery of some of the basic phenomena that occur during the interaction of intense light fields with atomic systems - such as multiphoton ionization (MPI), above-threshold ionization (ATI), and high harmonic generation (HHG). Also outlined are the related theoretical concepts and the nonperturbative "KFR model" for interpreting the phenomena. Recent observation of the breakdown of a popular "tunneling model" (Keldysh γ < 1) is noted and the role of discrete photon effects that can account for the observed parallel momentum distribution is given. Next, the role of e-e correlation in intense-field processes in many-electron atomic systems is discussed. A systematic analysis of intense-field problems using the "intense-field many-body S-matrix theory" (IMST) is outlined. To this end, the basic motivation behind and the derivation of IMST is discussed, and its use is illustrated by application to the problem of nonsequential double ionization (NSDI) that provided a fully quantum analysis of the mechanism behind the NSDI process. Also discussed is how NSDI and its opposite, sequential double ionization (SDI), can both occur in intense fields depending, respectively, on near-infrared and ultraviolet wavelengths of the light field used. A mechanism for multiple ionization is suggested by the IMST diagrams, which can provide a good estimate of the known experimental observations of the ion states vs. intensity in noble gases. Finally, an example is given of the spatial distributions of the charge states that can be produced in the focal region (a "flying reaction vessel"!) of an intense Ti:sapphire laser.
Inelastic Electron Tunneling Spectroscopy in Molecular Electronic Devices from First-Principles
NASA Astrophysics Data System (ADS)
Ji, Tao
In this thesis, we present the first-principle calculations of inelastic electron tunneling spectroscopy(IETS) in single molecular break junctions. In a two-probe electrode-molecule-electrode setup, density functional theory(DFT) is used for the construction of the Hamiltonian and the Keldysh non-equilibrium Green's function(NEGF) technique will be employed for determining the electron density in non-equilibrium system conditions. Total energy functional, atomic forces and Hessian matrix can be obtained in the DFT-NEGF formalism and self-consistent Born approximation(SCBA) is used to integrate the molecular vibrations (phonons) into the framework once the phonon spectra and eigenvectors are calculated from the dynamic matrix. Geometry optimization schemes will also be discussed as an indispensable part of the formalism as the equilibrium condition is crucial to correctly calculate the phonon properties of the system. To overcome the numerical difficulties, especially the large computational time demand of the electron-phonon coupling problem, we develop a numerical approximation for the electron self-energy due to phonons and the error is controlled within numerical precision. Besides, a direct IETS second order I-V derivative expression is derived to reduce the error of numerical differentiation under reasonable assumptions. These two approximations greatly reduce the computation requirement and make the calculation feasible within current numerical capability. As the application of the DFT-NEGF-SCBA formalism, we calculate the IETS of the gold-octanedithiol(ODT) molecular junction. The I-V curve, conductance and IETS from ab-inito calculations are compared directly to experiments. A microscopic understanding of the electron-phonon coupling mechanism in the molecular tunneling junctions is explained in this example. In addition, comparisons of the hydrogen-dissociative and hydrogen-non-dissociative ODT junctions as well as the different charge transfer behaviors
Scaling theory for anomalous semiclassical quantum transport
NASA Astrophysics Data System (ADS)
Sena-Junior, M. I.; Macêdo, A. M. S.
2016-01-01
Quantum transport through devices coupled to electron reservoirs can be described in terms of the full counting statistics (FCS) of charge transfer. Transport observables, such as conductance and shot-noise power are just cumulants of FCS and can be obtained from the sample's average density of transmission eigenvalues, which in turn can be obtained from a finite element representation of the saddle-point equation of the Keldysh (or supersymmetric) nonlinear sigma model, known as quantum circuit theory. Normal universal metallic behavior in the semiclassical regime is controlled by the presence of a Fabry-Pérot singularity in the average density of transmission eigenvalues. We present general conditions for the suppression of Fabry-Pérot modes in the semiclassical regime in a sample of arbitrary shape, a disordered conductor or a network of ballistic quantum dots, which leads to an anomalous metallic phase. Through a double-scaling limit, we derive a scaling equation for anomalous metallic transport, in the form of a nonlinear differential equation, which generalizes the ballistic-diffusive scaling equation of a normal metal. The two-parameter stationary solution of our scaling equation generalizes Dorokhov's universal single-parameter distribution of transmission eigenvalues. We provide a simple interpretation of the stationary solution using a thermodynamic analogy with a spin-glass system. As an application, we consider a system formed by a diffusive wire coupled via a barrier to normal-superconductor reservoirs. We observe anomalous reflectionless tunneling, when all perfectly transmitting channels are suppressed, which cannot be explained by the usual mechanism of disorder-induced opening of tunneling channels.
Dynamics and universality in noise-driven dissipative systems
NASA Astrophysics Data System (ADS)
Dalla Torre, Emanuele G.; Demler, Eugene; Giamarchi, Thierry; Altman, Ehud
2012-05-01
We investigate the dynamical properties of low-dimensional systems, driven by external noise sources. Specifically we consider a resistively shunted Josephson junction and a one-dimensional quantum liquid in a commensurate lattice potential, subject to 1/f noise. In absence of nonlinear coupling, we have shown previously that these systems establish a nonequilibrium critical steady state [Dalla Torre, Demler, Giamarchi, and Altman, Nat. Phys.1745-247310.1038/nphys1754 6, 806 (2010)]. Here, we use this state as the basis for a controlled renormalization group analysis using the Keldysh path integral formulation to treat the nonlinearities: the Josephson coupling and the commensurate lattice. The analysis to first order in the coupling constant indicates transitions between superconducting and localized regimes that are smoothly connected to the respective equilibrium transitions. However, at second order, the back action of the mode coupling on the critical state leads to renormalization of dissipation and emergence of an effective temperature. In the Josephson junction, the temperature is parametrically small allowing to observe a universal crossover between the superconducting and insulating regimes. The I-V characteristics of the junction displays algebraic behavior controlled by the underlying critical state over a wide range. In the noisy one-dimensional liquid, the generated dissipation and effective temperature are not small as in the junction. We find a crossover between a quasilocalized regime dominated by dissipation and another dominated by temperature. However, since in the thermal regime the thermalization rate is parametrically small, signatures of the nonequilibrium critical state may be seen in transient dynamics.
Modeling ion sensing in molecular electronics
Chen, Caroline J.; Smeu, Manuel Ratner, Mark A.
2014-02-07
We examine the ability of molecules to sense ions by measuring the change in molecular conductance in the presence of such charged species. The detection of protons (H{sup +}), alkali metal cations (M{sup +}), calcium ions (Ca{sup 2+}), and hydronium ions (H{sub 3}O{sup +}) is considered. Density functional theory (DFT) is used within the Keldysh non-equilibrium Green's function framework (NEGF) to model electron transport properties of quinolinedithiol (QDT, C{sub 9}H{sub 7}NS{sub 2}), bridging Al electrodes. The geometry of the transport region is relaxed with DFT. The transport properties of the device are modeled with NEGF-DFT to determine if this device can distinguish among the M{sup +} + QDT species containing monovalent cations, where M{sup +} = H{sup +}, Li{sup +}, Na{sup +}, or K{sup +}. Because of the asymmetry of QDT in between the two electrodes, both positive and negative biases are considered. The electron transmission function and conductance properties are simulated for electrode biases in the range from −0.5 V to 0.5 V at increments of 0.1 V. Scattering state analysis is used to determine the molecular orbitals that are the main contributors to the peaks in the transmission function near the Fermi level of the electrodes, and current-voltage relationships are obtained. The results show that QDT can be used as a proton detector by measuring transport through it and can conceivably act as a pH sensor in solutions. In addition, QDT may be able to distinguish among different monovalent species. This work suggests an approach to design modern molecular electronic conductance sensors with high sensitivity and specificity using well-established quantum chemistry.
Large-time evolution of an electron in photon bath
Kazakov, Kirill A.; Nikitin, Vladimir V.
2012-12-15
The problem of infrared divergence of the effective electromagnetic field produced by elementary charges is revisited using the model of an electron freely evolving in a photon bath. It is shown that for any finite travel time, the effective field of the electron is infrared-finite, and that at each order of perturbation theory the radiative contributions grow unboundedly with time. Using the Schwinger-Keldysh formalism, factorization of divergent contributions in multi-loop diagrams is proved, and summation of the resulting infinite series is performed. It is found that despite the unbounded growth of individual contributions to the effective field, their sum is bounded, tending to zero in the limit of infinite travel time. It is concluded that the physical meaning of infrared singularity in the effective field is the existence of a peculiar irreversible spreading of electric charges, caused by their interaction with the electromagnetic field. This spreading originates from the quantum electromagnetic fluctuations, rather than the electron-photon scattering, and exists in vacuum as well as at finite temperatures. It shows itself in a damping of the off-diagonal elements of the momentum-space density matrix of electron, but does not affect its momentum probability distribution. This effect is discussed in terms of thermalization of the electron state, and the asymptotic growth of its quantum entropy is determined. Relationship of the obtained results to the Bloch-Nordsieck theorem is established and considered from the standpoint of measurability of the electromagnetic field. The effect of irreversible spreading on the electron diffraction in the classic two-slit experiment is determined, and is shown to be detectable in principle by modern devices already at room temperature. - Highlights: Black-Right-Pointing-Pointer Infrared finiteness of the effective electromagnetic field of a free electron is proved. Black-Right-Pointing-Pointer Quantum radiative effects
NASA Astrophysics Data System (ADS)
Fokina, A.; Akhmanov, G.; Andreassen, K.
2013-12-01
Bottom sampling in several areas of the Barents Sea and sub-sampling of gases from collected sediments were carried out as part of various geological marine expeditions. These expeditions were organized by the UNESCO-MSU Training and Research Centre for Marine Geology and Geophysics of the Moscow State University (Russia) and the University of Tromso (Norway) onboard R/V "Akademik Nikolaj Strakhov" and R/V 'Helmer Hanssen' during the period of 2011-2013. A total of 304 gas samples from 51 different stations were analyzed using Gas Chromatography (GC) and Isotope Ratio Mass-Spectrometry (IRMS) techniques. These were combined in a database which was used to investigate the relationship between the type of depositional environment, hydrocarbon gas concentration and sediment composition. Gas samples, collected from shelf deposits, mainly consist of methane (90-99%) with little admixture of ethane and propane. Unsaturated homologues were detected in all samples. Ethylene and propylene predominate over saturated homologues. This, together with the isotopic composition, suggests a biogenic nature of the gases collected in most areas. Gas concentrations were found to be very low for the majority of analyzed sediment samples. This is indicative for their low filtration capacity and low organic matter content. The cause of this is believed to be the pelitic clayey composition of the sediments, their high compaction and the generally frugal bioproductivity in arctic regions. A specific molecular and isotopic composition and high concentrations of gas are characteristic for the zones of focused hydrocarbon seepage on the seafloor that were studied during the cruises. Areas with pockmarks, outcropping salt diapirs and gas flares above the seafloor were classified high petroleum potentials, such as the Hjalmar Johansen High and the North-Kildenskoe gas field, was examined in order to verify characteristics of gas emission from deeply seated accumulations of natural hydrocarbon
NASA Astrophysics Data System (ADS)
Ivanova, E. V.; Borisov, D.; Murdmaa, I.; Levchenko, O. V.; Dmitrenko, O.; Emelyanov, E.
2014-12-01
The high-resolution seismic profiling during cruise 32 of the RV "Akademik Ioffe" (2010) discovered a large elongated contourite drift on the ridge of the Rio Grande fracture zone (Brazil Basin, western South Atlantic). This sedimentary body with a thickness up to 300 m, named Ioffe drift, is traced at water depth range from 3790 to 3980 m. Five seismic units are distinguished within the upper drift structure recorded to a depth of 60 mbsf. The seismic units are separated by angular discontinuities. The sediment core AI-2436 (25°51.6'S, 34°01.40'W, water depth 3800 m) retrieved near the drift top recovers about 6 m of nanno-foraminiferal ooze intercalated with foraminiferal sand interbeds. According to the planktonic foraminiferal and nannofossil stratigraphy, the sediment record embraces about 3 My of the Ioffe drift history, from the Late Pliocene to present. Absence of several foraminiferal and nannofossil zones in the core section indicates long-term hiatuses. Some zones are thicker here while others are reduced as compared to those on the nearby Rio Grande Rise. This suggests reworking of the biogenic material in the drift. The Ioffe drift was formed as a result of transport and deposition of biogenic calcareous material by the eastern branch of the Antarctic bottom water (AABW) flow. The biogenic calcareous material is mainly derived from the Rio Grande Rise where planktonic foraminiferal and nannofossil assemblages identical to those in core AI-2436 are studied at the DSDP site 516 (Barash et al., 1983). We suggest that the grain-size distribution of the calcareous sediments roughly corresponding to the foraminiferal/nannofossil ratio reflects the bottom currents velocity variations. Very high current velocities result in erosion and stratigraphic hiatuses. Angular unconformities in seismic profiles indicate episodes of intensified AABW flow velocity which led to the drift migration. The study was supported by RFBR, research projects 14-05-31357-mol_a, 14
Arctic satellite thermal infrared CH4 data compared to surface in-situ and total column measurements
NASA Astrophysics Data System (ADS)
Yurganov, L.; Leifer, I.; Xiong, X.
2013-12-01
The trace gas sensitivity of Thermal InfraRed (TIR) sounders (AIRS, IASI, TANSO) is greatest in the middle and upper troposphere; though, lower troposphere (1-2 km of altitude) sensitivity is less but not negligible. As a result, where methane largely is constrained to the lower troposphere, as is common in the Arctic particularly the marine Arctic, retrievals from these instruments provides important synoptic data on high latitude methane sources. Low Arctic water vapor content favors a better sensitivity to methane as well: H2O is the main absorber in the 7.8 micrometers spectral region. Both AIRS/Aqua v6 (NASA) and IASI/Metop-A (NOAA/NESDIS/CLASS retrievals) methane data averaged over 0-4 km altitude clearly demonstrate increased methane concentrations over the Barents and Norwegian Seas (BNS) with seasonal maximum in December - March. Similar increases are observed over the Kara, Laptev, and Chukchi Seas for September-November, i.e. during the period of minimum ice cover over the Arctic (Figures 1 and 2). Comparison of a long series of AIRS data with in situ methane concentrations at the Zeppelin NILU observatory (Svalbard) show good agreement both in amplitude and phase of seasonal variations. Agreement with Barrow NOAA continuous methane in situ data is much worse, which likely results from lower thermal contrast in winter over the cold and icy surfaces of the Eastern Arctic. Further surface validation is by a comparison of total methane columns with the Sun-Tracking FTIR at Ny-Alesund, Svalbard (TCCON network). These analyses demonstrate that TIR satellites are capable of detecting Arctic methane enhancements from space, particularly over relatively warm year-round water surfaces such as the BNS. Ongoing research is addressing further verification of retrieved methane columns by collecting data with a cavity ring-down spectroscopy analyzer for methane and carbon dioxide on board of the Russian Research Vessel Akademik Fedorov during the expedition NABOS-2013
NASA Astrophysics Data System (ADS)
Fokina, A.; Akhmanov, G.; Andreassen, K.; Yurchenko, A.
2014-12-01
In 2011-2013 four research cruises in the Barents Sea were organized by UNESCO-MSU Centre for Marine Geology and Geophysics (Russia) and University of Tromso (Norway) and were carried out onboard the RV "Akademik N. Strakhov" and RV "Helmer Hanssen". The cruises were devoted to finding and studying hydrocarbon seeps (e.g. pockmarks, crater-like structures), evaluating neo-tectonic activity and focusing on some problems in the field of modern geological and geochemical processes in the Arctic region. This topic is focused on identification of the gas anomalies related to the possible cold seep structures, study of the molecular and isotopic composition and origin of the hydrocarbon gases from the bottom sediments. During this research the interpretation of geochemical survey data was carried out within the different structures of the Barents region: 1) The area of distribution of craters, 2) Storfjordrenna and Storfiordbanken, 3) Nordkap and Tiddly basins, Fedynskii high, North-Kildinsk field. 1) In the Central Barents Sea in the area of distribution of craters residual discharge of gas from the Triassic sandstones has occurred and manifested through the activity of gas flares and elevated concentrations of methane. Values of gas coefficients indicate the possible existence of thermogenic gas in the sample. The active unloading of gas and formation of craters associated with the disintegration of gas hydrates. 2) Discovered gas flares, pockmarks and abnormal high concentrations of methane are the first statement about the presence of active gas discharge in the NW Barents Sea. HC gases are formed as a result of microbial processing of thermogenic gas. In the area there is an increased microbial activity resulting in authigenic carbonate formation. Unloading of gas is observed in the edges parts of the large glacial moraine along the base of which the lateral migration of gas occurs. Reservoirs can be Lower-Middle and Lower-Middle Triassic sandstones. 3) In the
NASA Astrophysics Data System (ADS)
Lembke-Jene, L.; Biebow, N.; Wolff-Boenisch, B.; Thiede, J.; European Research Icebreaker Consortium
2011-12-01
Research vessels dedicated to work in polar ice-covered waters have only rarely been built. Their history began with Fritjof Nansen's FRAM, which he used for his famous first crossing of the Arctic Ocean 1893-1896. She served as example for the first generation of polar research vessels, at their time being modern instruments planned with foresight. Ice breaker technology has developed substantially since then. However, it took almost 80 years until this technical advance also reached polar research, when the Russian AKADEMIK FEDEROV, the German POLARSTERN, the Swedish ODEN and the USCG Cutter HEALY were built. All of these house modern laboratories, are ice-breakers capable to move into the deep-Arctic during the summer time and represent the second generation of dedicated polar research vessels. Still, the increasing demand in polar marine research capacities by societies that call for action to better understand climate change, especially in the high latitudes is not matched by adequate facilities and resources. Today, no icebreaker platform exists that is permanently available to the international science community for year-round expeditions into the central Arctic Ocean or heavily ice-infested waters of the polar Southern Ocean around Antarctica. The AURORA BOREALIS concept plans for a heavy research icebreaker, which will enable polar scientists around the world to launch international research expeditions into the central Arctic Ocean and the Antarctic continental shelf seas autonomously during all seasons of the year. The European Research Icebreaker Consortium - AURORA BOREALIS (ERICON-AB) was established in 2008 to plan the scientific, governance, financial, and legal frameworks needed for the construction and operation of this first multi-nationally owned and operated research icebreaker and polar scientific drilling platform. By collaborating together and sharing common infrastructures it is envisioned that European nations make a major contribution to
NASA Astrophysics Data System (ADS)
Gritsenko, Alexander; Tarakanov, Roman
2016-04-01
Fine jet structure of the Antarctic Circumpolar Current (ACC) in the Drake Passage is investigated on the basis of the daily satellite data of the absolute dynamic topography (ADT) provided by the French CLS Agency (DT-Global-MADT-Upd product, http://aviso.oceanobs.com) and sea surface temperature (SST) provided by the GAMSSA Project (Global Australian Multi-Sensor SST Analysis, http://data.nodc.noaa.gov/las/getUI.do?dsid=id-c80878d11f&varid=analysed_sst-id-c80878d11f&auto=true) of the Centre for Australian Weather and Climate Research. The investigation was executed on 01.09.2011-31.12.2011 using the methods of the probability-statistical analysis. Mesoscale eddies were eliminated from the analysis of fine jet structure of the ACC in the Drake Passage. As a result the amplitude of the ADT and SST gradients increased. This allowed us to distinguish more precisely the limits and cores of the jets. The jet limits were chosen as the isopleths of the ADT (isohypses) matching with the local minima of the ADT and SST gradients (averaged in time) along ADT axis in ADT-gradient-ADT and SST-gradient-ADT spaces, while the cores of the jets coincided with the local maxima of the SST and ADT gradients at the corresponding isohypses. The main feature of the studied region is merging of the separated jets into a powerful "superjet" as the ACC passes through the passage. It is possible to separate and identify these separated jets if we have auxiliary (e.g. sub-satellite) information. With this in mind we used the CTD- and SADCP-measurements over the section carried out on 28.10.2011-04.11.2011 onboard R/V "Akademik Ioffe" across the Drake Passage. The analyses of the satellite data revealed 8-9 individual jets characterized by the local horizontal maxima of the ADT and SST gradients. These jets were actually various combinations of the twelve ACC jets, which we found earlier south of Africa. In September-October 2011, we found 6 jets of the Subantarctic Current, 4 jets of the
Ecological state of North -Western Black Sea macrobenthos on offshore bottoms deeper than 50 m
NASA Astrophysics Data System (ADS)
Gomoiu, M.-T.; Begun, T.; Teaca, A.
2009-04-01
In the last 10-15 years researches concerning benthos in the north-western Black Sea were focused mainly on inshore bottoms, usually less than 50 m deep, where important ecological changed occurred. The offshore bottoms, deeper than 50 m, and especially the periazoic level at the edge of the continental shelf have been less known, the information being scarce. The present study gathers the results of the researches carried out in the past 12 years on the Modiolus phaseolinus community, including the periazoic level, and allows a comparison to be drawn with the situation of the so-called "ecological stability" period at the beginning of the 1960s, before the ecosystemic disturbances began in the Black Sea. In 1995-2007, a number of 133 quantitative macro-benthos samples were collected at depths of 50 - 213 m by means of the van Veen-type grab and box corer; these samples were taken during several cruises (R/V "Prof.Vodyanitskyi" EROS 1995, 1997, R/V „Akademik" 2003, R/V „Parshin" 2005, R/V „Akademik" 2006 R/V „Mare Nigrum" 2006 and 2007), the researches aiming at the assessment of the benthic ecosystem state. The analyses of the 133 samples helped identify 191 taxa (Vermes - 88, Mollusca - 24, Crustacea - 32 and Varia - 47), approximately 60% of the total number of species recorded in the north-western Black Sea during the period of "ecological prosperity". The mean abundance of the benthic populations was 4,836.2 indvs.m-2 for density and 189.9 g.m-2 for biomass. Most macrobenthic taxa occurred in the samples accidentally; out of the 191 taxa recorded, 60 taxa had a frequency of 1-2%, 37 taxa 2-5%, 28 taxa 5-10%, 32 taxa 10-20%, 26 taxa 20-50% and only eight species had a frequency over 50% (Modiolus phaseolinus, Terebelides stroemi, Capitella capitata, Nephtys hombergi, Amphiura stepanovi, Sphaerosyllis bulbosa, Apseudes ostroumovi and Phyllodoce lineata). Numerical abundances were dominated by worms (2,606.9 indvs.m-2) and molluscs (1,398.7 indvs.m-2
Ecological state of North -Western Black Sea macrobenthos on offshore bottoms deeper than 50 m
NASA Astrophysics Data System (ADS)
Gomoiu, M.-T.; Begun, T.; Teaca, A.
2009-04-01
In the last 10-15 years researches concerning benthos in the north-western Black Sea were focused mainly on inshore bottoms, usually less than 50 m deep, where important ecological changed occurred. The offshore bottoms, deeper than 50 m, and especially the periazoic level at the edge of the continental shelf have been less known, the information being scarce. The present study gathers the results of the researches carried out in the past 12 years on the Modiolus phaseolinus community, including the periazoic level, and allows a comparison to be drawn with the situation of the so-called "ecological stability" period at the beginning of the 1960s, before the ecosystemic disturbances began in the Black Sea. In 1995-2007, a number of 133 quantitative macro-benthos samples were collected at depths of 50 - 213 m by means of the van Veen-type grab and box corer; these samples were taken during several cruises (R/V "Prof.Vodyanitskyi" EROS 1995, 1997, R/V „Akademik" 2003, R/V „Parshin" 2005, R/V „Akademik" 2006 R/V „Mare Nigrum" 2006 and 2007), the researches aiming at the assessment of the benthic ecosystem state. The analyses of the 133 samples helped identify 191 taxa (Vermes - 88, Mollusca - 24, Crustacea - 32 and Varia - 47), approximately 60% of the total number of species recorded in the north-western Black Sea during the period of "ecological prosperity". The mean abundance of the benthic populations was 4,836.2 indvs.m-2 for density and 189.9 g.m-2 for biomass. Most macrobenthic taxa occurred in the samples accidentally; out of the 191 taxa recorded, 60 taxa had a frequency of 1-2%, 37 taxa 2-5%, 28 taxa 5-10%, 32 taxa 10-20%, 26 taxa 20-50% and only eight species had a frequency over 50% (Modiolus phaseolinus, Terebelides stroemi, Capitella capitata, Nephtys hombergi, Amphiura stepanovi, Sphaerosyllis bulbosa, Apseudes ostroumovi and Phyllodoce lineata). Numerical abundances were dominated by worms (2,606.9 indvs.m-2) and molluscs (1,398.7 indvs.m-2
Photon-assisted tunneling through mesoscopic systems
NASA Astrophysics Data System (ADS)
Niu, Cheng
2000-11-01
perturbation expansion and graph technique is well developed by Keldysh. However, the equation of motion, which is a convenient form for numerical computation, involves undefined singularities, and cannot be applied independently. In this thesis, we developed the equation of motion for non-equilibrium GF, and derive the explicit form of the singularity. The equation of motion for non-equlibrium GF is the main tool for theoretical computation throughout this thesis.
Nonlinear quantum transport in low-dimensional electronic devices
NASA Astrophysics Data System (ADS)
Barrios, Andres Javier
The study of transport processes in low-dimensional semiconductors requires a rigorous quantum mechanical treatment. However, a full-fledged quantum transport theory of electrons (or holes) in semiconductors of small scale, applicable in the presence of external fields of arbitrary strength, is still not available. In the literature, different approaches have been proposed, including: (a) the semiclassical Boltzmann equation, (b) perturbation theory based on Keldysh's Green functions, and (c) the Quantum Boltzmann Equation (QBE), previously derived by Van Vliet and coworkers, applicable in the realm of Kubo's Linear Response Theory (LRT). In the present work, we follow the method originally proposed by Van Wet in LRT. The Hamiltonian in this approach is of the form: H = H 0(E, B) + lambdaV, where H0 contains the externally applied fields, and lambdaV includes many-body interactions. This Hamiltonian differs from the LRT Hamiltonian, H = H0 - AF(t) + lambdaV, which contains the external field in the field-response part, -AF(t). For the nonlinear problem, the eigenfunctions of the system Hamiltonian, H0(E, B), include the external fields without any limitation on strength. In Part A of this dissertation, both the diagonal and nondiagonal Master equations are obtained after applying projection operators to the von Neumann equation for the density operator in the interaction picture, and taking the Van Hove limit, (lambda → 0, t → infinity, so that (lambda2 t)n remains finite). Similarly, the many-body current operator J is obtained from the Heisenberg equation of motion. In Part B, the Quantum Boltzmann Equation is obtained in the occupation-number representation for an electron gas, interacting with phonons or impurities. On the one-body level, the current operator obtained in Part A leads to the Generalized Calecki current for electric and magnetic fields of arbitrary strength. Furthermore, in this part, the LRT results for the current and conductance are
Strong correlations in gravity and biophysics
NASA Astrophysics Data System (ADS)
Krotov, Dmitry
The unifying theme of this dissertation is the use of correlations. In the first part (chapter 2), we investigate correlations in quantum field theories in de Sitter space. In the second part (chapters 3,4,5), we use correlations to investigate a theoretical proposal that real (observed in nature) transcriptional networks of biological organisms are operating at a critical point in their phase diagram. In chapter 2 we study the infrared dependence of correlators in various external backgrounds. Using the Schwinger-Keldysh formalism we calculate loop corrections to the correlators in the case of the Poincare patch and the complete de Sitter space. In the case of the Poincare patch, the loop correction modifies the behavior of the correlator at large distances. In the case of the complete de Sitter space, the loop correction has a strong dependence on the infrared cutoff in the past. It grows linearly with time, suggesting that at some point the correlations become strong and break the symmetry of the classical background. In chapter 3 we derive the signatures of critical behavior in a model organism, the embryo of Drosophila melanogaster. They are: strong correlations in the fluctuations of different genes, a slowing of dynamics, long range correlations in space, and departures from a Gaussian distribution of these fluctuations. We argue that these signatures are observed experimentally. In chapter 4 we construct an effective theory for the zero mode in this system. This theory is different from the standard Landau-Ginsburg description. It contains gauge fields (the result of the broken translational symmetry inside the cell), which produce observable contributions to the two-point function of the order parameter. We show that the behavior of the two-point function for the network of N genes is described by the action of a relativistic particle moving on the surface of the N - 1 dimensional sphere. We derive a theoretical bound on the decay of the correlations and
Strong-field and attosecond physics in solids
Ghimire, Shambhu; Ndabashimiye, Georges; DiChiara, Anthony D.; Sistrunk, Emily; Stockman, Mark I.; Agostini, Pierre; DiMauro, Louis F.; Reis, David A.
2014-10-08
We review the status of strong-field and attosecond processes in bulk transparent solids near the Keldysh tunneling limit. For high enough fields and low-frequency excitations, the optical and electronic properties of dielectrics can be transiently and reversibly modified within the applied pulse. In Ghimire et al (2011 Phys. Rev. Lett. 107 167407) non-parabolic band effects were seen in photon-assisted tunneling experiments in ZnO crystals in a strong mid-infrared field. Using the same ZnO crystals, Ghimire et al (2011 Nat. Phys. 7 138–41) reported the first observation of non-pertubative high harmonics, extending well above the bandgap into the vacuum ultraviolet. Recent experiments by Schubert et al (2014 Nat. Photonics 8 119–23) showed a carrier envelope phase dependence in the harmonic spectrum in strong-field 30 THz driven GaSe crystals which is the most direct evidence yet of the role of sub-cycle electron dynamics in solid-state harmonic generation. The harmonic generation mechanism is different from the gas phase owing to the high density and periodicity of the crystal. For example, this results in a linear dependence of the high-energy cutoff with the applied field in contrast to the quadratic dependence in the gas phase. Sub-100 attosecond pulses could become possible if the harmonic spectrum can be extended into the extreme ultraviolet (XUV). Here we report harmonics generated in bulk MgO crystals, extending to $\\sim 26$ eV when driven by ~35 fs, 800 nm pulses focused to a ~1 VÅ$^{-1}$ peak field. The fundamental strong-field and attosecond response also leads to Wannier–Stark localization and reversible semimetallization as seen in the sub-optical cycle behavior of XUV absorption and photocurrent experiments on fused silica by Schiffrin et al (2013 Nature 493 70–4) and Schultze et al (2013 Nature 493 75–8). These studies are advancing our understanding of fundamental strong-field and attosecond physics in solids with potential applications
Non-equilibrium STLS approach to transport properties of single impurity Anderson model
Rezai, Raheleh Ebrahimi, Farshad
2014-04-15
In this work, using the non-equilibrium Keldysh formalism, we study the effects of the electron–electron interaction and the electron-spin correlation on the non-equilibrium Kondo effect and the transport properties of the symmetric single impurity Anderson model (SIAM) at zero temperature by generalizing the self-consistent method of Singwi, Tosi, Land, and Sjolander (STLS) for a single-band tight-binding model with Hubbard type interaction to out of equilibrium steady-states. We at first determine in a self-consistent manner the non-equilibrium spin correlation function, the effective Hubbard interaction, and the double-occupancy at the impurity site. Then, using the non-equilibrium STLS spin polarization function in the non-equilibrium formalism of the iterative perturbation theory (IPT) of Yosida and Yamada, and Horvatic and Zlatic, we compute the spectral density, the current–voltage characteristics and the differential conductance as functions of the applied bias and the strength of on-site Hubbard interaction. We compare our spectral densities at zero bias with the results of numerical renormalization group (NRG) and depict the effects of the electron–electron interaction and electron-spin correlation at the impurity site on the aforementioned properties by comparing our numerical result with the order U{sup 2} IPT. Finally, we show that the obtained numerical results on the differential conductance have a quadratic universal scaling behavior and the resulting Kondo temperature shows an exponential behavior. -- Highlights: •We introduce for the first time the non-equilibrium method of STLS for Hubbard type models. •We determine the transport properties of SIAM using the non-equilibrium STLS method. •We compare our results with order-U2 IPT and NRG. •We show that non-equilibrium STLS, contrary to the GW and self-consistent RPA, produces the two Hubbard peaks in DOS. •We show that the method keeps the universal scaling behavior and correct
Mongolian-Russian cooperation at the Khureltogoot observatory in the ISON project framework
NASA Astrophysics Data System (ADS)
Tungalag, Namkhai; Rentsenmyagmar, Buyankhishig; Turmunkh, Bayarbat; Tsogt-Ochir, Shijirbayar; Molotov, Igor; Voropaev, Viktor; Kouprianov, Vladimir; Krugly, Yury; Schmalz, Sergey; Pozanenko, Aleksey
2014-09-01
Since autumn 2012, the Research Center of Astronomy and Geophysics, Academy of Sciences of Mongolia, in collaboration with the International Scientific Optical Network (ISON) coordinated by the Keldysh Institute for Applied Mathematics (KIAM), Russian Academy of Sciences, have conducted a large number of astronomical observations of space debris, asteroids, and the optical afterglows of gamma-ray bursts (GRBs) at the new facility of the Khureltogoot observatory near Ulaanbaatar. To the date, ISON joins 35 observation facilities with 80 telescopes of apertures from 12.5 cm to 2.6 m in 15 countries and carries out research on space debris, asteroids, and GRBs. 8.4 million measurements in 1.21 million tracklets of about 4000 Earth-orbiting objects were collected by the ISON network in 2013. It is planned that a part of the orbital data will be accessible via a UN-hosted web page in 2014. A new pavilion was built at Khureltogoot during 2012 to initiate collaboration with ISON. Since November 2012, observations began with the VT-78a 19.2 cm telescopes, with a field of view of 7×7 degrees on a robotic WS-180 mount. The telescope is controlled by the CHAOS TCS software; CCD image processing is done using the APEX II software platform developed within the ISON project. This telescope provides extended surveys of a visible part of the geostationary ring from 0 to 20 degrees inclination, with up to 15 thousand measurements of 500 to 700 objects per night. The limiting magnitude is 14 mag for 10 s exposure time, while the time span of individual tracklets is up to several hours. These surveys help KIAM to increase the accuracy of geostationary Earth-orbit (GEO) object orbits for conjunction analysis, to detect maneuvers of active satellites, and to assist in maintaining the orbits of GEO objects in clusters. Moreover, many HEO objects are detected as a by-product. Since November 2013, a new 40 cm telescope, ORI-40 with the field of view of 2.3×2.3 degrees on a robotic WS
Recent progress of probing correlated electron states by point contact spectroscopy
NASA Astrophysics Data System (ADS)
Lee, Wei-Cheng; Greene, Laura H.
2016-09-01
We review recent progress in point contact spectroscopy (PCS) to extract spectroscopic information out of correlated electron materials, with the emphasis on non-superconducting states. PCS has been used to detect bosonic excitations in normal metals, where signatures (e.g. phonons) are usually less than 1% of the measured conductance. In the superconducting state, point contact Andreev reflection (PCAR) has been widely used to study properties of the superconducting gap in various superconductors. It has been well-recognized that the corresponding conductance can be accurately fitted by the Blonder–Tinkham–Klapwijk (BTK) theory in which the AR occurring near the point contact junction is modeled by three parameters; the superconducting gap, the quasiparticle scattering rate, and a dimensionless parameter, Z, describing the strength of the potential barrier at the junction. AR can be as large as 100% of the background conductance, and only arises in the case of superconductors. In the last decade, there have been more and more experimental results suggesting that the point contact conductance could reveal new features associated with the unusual single electron dynamics in non-superconducting states, shedding a new light on exploring the nature of the competing phases in correlated materials. To correctly interpret these new features, it is crucial to re-examine the modeling of the point contact junctions, the formalism used to describe the single electron dynamics particularly in point contact spectroscopy, and the physical quantity that should be computed to understand the conductance. We will summarize the theories for point contact spectroscopy developed from different approaches and highlight these conceptual differences distinguishing point contact spectroscopy from tunneling-based probes. Moreover, we will show how the Schwinger–Kadanoff–Baym–Keldysh (SKBK) formalism together with the appropriate modeling of the nano-scale point contacts randomly
Control of noisy quantum systems: Field-theory approach to error mitigation
NASA Astrophysics Data System (ADS)
Hipolito, Rafael; Goldbart, Paul M.
2016-04-01
We consider the basic quantum-control task of obtaining a target unitary operation (i.e., a quantum gate) via control fields that couple to the quantum system and are chosen to best mitigate errors resulting from time-dependent noise, which frustrate this task. We allow for two sources of noise: fluctuations in the control fields and fluctuations arising from the environment. We address the issue of control-error mitigation by means of a formulation rooted in the Martin-Siggia-Rose (MSR) approach to noisy, classical statistical-mechanical systems. To do this, we express the noisy control problem in terms of a path integral, and integrate out the noise to arrive at an effective, noise-free description. We characterize the degree of success in error mitigation via a fidelity metric, which characterizes the proximity of the sought-after evolution to ones that are achievable in the presence of noise. Error mitigation is then best accomplished by applying the optimal control fields, i.e., those that maximize the fidelity subject to any constraints obeyed by the control fields. To make connection with MSR, we reformulate the fidelity in terms of a Schwinger-Keldysh (SK) path integral, with the added twist that the "forward" and "backward" branches of the time contour are inequivalent with respect to the noise. The present approach naturally and readily allows the incorporation of constraints on the control fields—a useful feature in practice, given that constraints feature in all real experiments. In addition to addressing the noise average of the fidelity, we consider its full probability distribution. The information content present in this distribution allows one to address more complex questions regarding error mitigation, including, in principle, questions of extreme value statistics, i.e., the likelihood and impact of rare instances of the fidelity and how to harness or cope with their influence. We illustrate this MSR-SK reformulation by considering a model
Efficient Sub-Bandgap Light Absorption and Signal Amplification in Silicon Photodetectors
NASA Astrophysics Data System (ADS)
Liu, Yu-Hsin
This thesis focuses on two areas in silicon photodetectors, the first being enhancing the sub-bandgap light absorption of IR wavelenghts in silicon, and the second being intrinsic signal amplification in silicon photodetectors. Both of these are achieved using heavily doped p-n junction devices which create localized states that relax the k-selection rule of indirect bandgap material. The probability of transitions between impurity band and the conduction/valence band would be much more efficient than the one between band-to-band transition. The waveguide-coupled epitaxial p-n photodetector was demonstrated for 1310 nm wavelength detection. Incorporated with the Franz-Keldysh effect and the quasi-confined epitaxial layer design, an absorption coefficient around 10 cm-1 has been measured and internal quantum efficiency nearly 100% at -2.5V. The absorption coefficient is calculated from the wave function of the electron and hole in p-n diode. The heavily doped impurity wave function can be formulated as a delta function, and the quasi-confined conduction band energy states, and the wave function on each level can be obtained from the Silvaco software. The calculated theoretical absorption coefficient increases with the increasing applied bias and the doping concentration, which matches the experimental results. To solve the issues of large excess noise and high operation bias for avalanche photodiodes based on impact ionization, I presented a detector using the Cycling Excitation Process (CEP) for signal amplification. This can be realized in a heavily doped and highly compensated Si p-n junction, showing ultra high gain about 3000 at very low bias (<4 V), and possessing an intrinsic, phonon-mediated regulation process to keep the device stable without any quenching device required in today's Geiger-mode avalanche detectors. The CEP can be formulated with the rate equations in conduction bands and impurity states. The gain expression, which is a function of the
Strong-field and attosecond physics in solids
Ghimire, Shambhu; Ndabashimiye, Georges; DiChiara, Anthony D.; Sistrunk, Emily; Stockman, Mark I.; Agostini, Pierre; DiMauro, Louis F.; Reis, David A.
2014-10-08
We review the status of strong-field and attosecond processes in bulk transparent solids near the Keldysh tunneling limit. For high enough fields and low-frequency excitations, the optical and electronic properties of dielectrics can be transiently and reversibly modified within the applied pulse. In Ghimire et al (2011 Phys. Rev. Lett. 107 167407) non-parabolic band effects were seen in photon-assisted tunneling experiments in ZnO crystals in a strong mid-infrared field. Using the same ZnO crystals, Ghimire et al (2011 Nat. Phys. 7 138–41) reported the first observation of non-pertubative high harmonics, extending well above the bandgap into the vacuum ultraviolet. Recent experiments by Schubert et al (2014 Nat. Photonics 8 119–23) showed a carrier envelope phase dependence in the harmonic spectrum in strong-field 30 THz driven GaSe crystals which is the most direct evidence yet of the role of sub-cycle electron dynamics in solid-state harmonic generation. The harmonic generation mechanism is different from the gas phase owing to the high density and periodicity of the crystal. For example, this results in a linear dependence of the high-energy cutoff with the applied field in contrast to the quadratic dependence in the gas phase. Sub-100 attosecond pulses could become possible if the harmonic spectrum can be extended into the extreme ultraviolet (XUV). Here we report harmonics generated in bulk MgO crystals, extending tomore » $$\\sim 26$$ eV when driven by ~35 fs, 800 nm pulses focused to a ~1 VÅ$$^{-1}$$ peak field. The fundamental strong-field and attosecond response also leads to Wannier–Stark localization and reversible semimetallization as seen in the sub-optical cycle behavior of XUV absorption and photocurrent experiments on fused silica by Schiffrin et al (2013 Nature 493 70–4) and Schultze et al (2013 Nature 493 75–8). These studies are advancing our understanding of fundamental strong-field and attosecond physics in solids with potential
GEO Population Estimates using Optical Survey Data
NASA Technical Reports Server (NTRS)
Barker, Edwin S.; Matney, Mark J.
2007-01-01
/CTIO, Astronomical Institute University of Bern, Boeing LTS / AMOS, Keldysh Institute of Applied Mathematics) at different longitudes. Complete observational coverage over periods of days to months will provide a better understanding of the properties, such as solar radiation pressure effects on orbital elements, size, shape, attitude, color variations, and spectral characteristics. Results from recent observational programs will be summarized, and includes a description of the orbit elements prediction processes, a summary of the metric tracking performance, and some photometric characteristics of this class of debris.
NASA Astrophysics Data System (ADS)
Rylyuk, V. M.
2016-05-01
Within the framework of the quasistationary quasienergy state (QQES) formalism, the tunneling and multiphoton ionization of atoms and ions subjected to a perturbation by a high intense laser radiation field of an arbitrary polarization and a constant magnetic field are considered. On the basis of the exact solution of the Schrödinger equation and the Green's function for the electron moving in an arbitrary laser field and crossed constant electric and magnetic fields, the integral equation for the complex quasienergy and the energy spectrum of the ejected electron are derived. Using the "imaginary-time" method, the extremal subbarrier trajectory of the photoelectron moving in a nonstationary laser field and a constant magnetic field are considered. Within the framework of the QQES formalism and the quasiclassical perturbation theory, ionization rates when the Coulomb interaction of the photoelectron with the parent ion is taken into account at arbitrary values of the Keldysh parameter are derived. The high accuracy of rates is confirmed by comparison with the results of numerical calculations. Simple analytical expressions for the ionization rate with the Coulomb correction in the tunneling and multiphoton regimes in the case of an elliptically polarized laser beam propagating at an arbitrary angle to the constant magnetic field are derived and discussed. The limits of small and large magnetic fields and low and high frequency of a laser field are considered in details. It is shown that in the presence of a nonstationary laser field perturbation, the constant magnetic field may either decrease or increase the ionization rate. The analytical consideration and numerical calculations also showed that the difference between the ionization rates for an s electron in the case of right- and left-elliptically polarized laser fields is especially significant in the multiphoton regime for not-too-high magnetic fields and decreases as the magnetic field increases. The paper
Electron Dynamics in Finite Quantum Systems
NASA Astrophysics Data System (ADS)
McDonald, Christopher R.
investigate a wide variety of problems that cannot be currently treated by any other method. Finally, the time it takes for an electron to tunnel from a bound state is investigated; a definition of the tunnel time is established and the Keldysh time is connected to the wavefunction dynamics.
Ultrafast and nonlinear optics in carbon nanomaterials.
Kono, Junichiro
2013-02-01
Carbon-based nanomaterials—single-wall carbon nanotubes (SWCNTs) and graphene, in particular—have emerged in the last decade as novel low-dimensional systems with extraordinary properties. Because they are direct-bandgap systems, SWCNTs are one of the leading candidates to unify electronic and optical functions in nanoscale circuitry; their diameter-dependent bandgaps can be utilized for multi-wavelength devices. Graphene's ultrahigh carrier mobilities are promising for high-frequency electronic devices, while, at the same time, it is predicted to have ideal properties for terahertz generation and detection due to its unique zero-gap, zero-mass band structure. There have been a large number of basic optical studies on these materials, but most of them were performed in the weak-excitation, quasi-equilibrium regime. In order to probe and assess their performance characteristics as optoelectronic materials under device-operating conditions, it is crucial to strongly drive them and examine their optical properties in highly non-equilibrium situations and with ultrashot time resolution. In this section, the reader will find the latest results in this rapidly growing field of research. We have assembled contributions from some of the leading experts in ultrafast and nonlinear optical spectroscopy of carbon-based nanomaterials. Specific topics featured include: thermalization, cooling, and recombination dynamics of photo-generated carriers; stimulated emission, gain, and amplification; ultrafast photoluminescence; coherent phonon dynamics; exciton–phonon and exciton–plasmon interactions; exciton–exciton annihilation and Auger processes; spontaneous and stimulated emission of terahertz radiation; four-wave mixing and harmonic generation; ultrafast photocurrents; the AC Stark and Franz–Keldysh effects; and non-perturbative light–mater coupling. We would like to express our sincere thanks to those who contributed their latest results to this special section
Russian Internet: Graduated from the Moscow State University
NASA Astrophysics Data System (ADS)
Gaina, Alex B.
2005-09-01
The purpose of the internet proceeding is 1) To give a complete list of publications of the Astronomer V.A.Albitzky (V.A.Albitzkij, b. 1892, Kishinev- d. 1952, Simeiz), graduated from the Moscow State University in 1916. Two photo of the astronomer are placed: http://upmsu.phys.msu.ru/1977/gaina/Albitzky.jpg and http://upmsu.phys.msu.ru/1977/gaina/Albitzky1.jpg 2) to make a review of the problem of Bound States in Black Holes evaporation. 3) A report on the works of the school "Quantum Particles in intensive fields" (Chisinau (Kishinev), 5-9 May, 1985), with photographs (see: http://upmsu.phys.msu.ru/1977/gaina/Out2.jpg) is added. In 1987 at the Shtiintsa eds. (Kishinev) a book: "Quantum processes in intensive fields" (Russian title: "Kvantovyie processy v intensivnyh polyah"), Kishinev Izdatel Shtiintsa, 1987 was published with lectures of the school held by the followuing scientists: Keldysh, L.V., Vaitkus, Yu.Yu., Khadzhi, P.I. et al., Mazets, T.F. et al., Bogolyubov, N.N. Jr. et al., Laptinskaya T.V. et al., Aktsipetrov, O.A., et al., Bobrysheva, A.I. et al., Buzdin, A.I., Golant K.M. et al., Bagrov, V.G. et al., Oleinik, V.P., Borisov, A.V. et al., Rodionov, V.N. et al., Teryeaev, O.V., Gal'tsov, D.V., Buchbinder, I.L. et al., Odintsov, S.D., Zhuk, A.I. The abstracts of the Lectures book can be found at ADS NASA 4) A report on a glory, observed by author in 1988 in the airship, around the umbra of the airship on clouds, flying above Crimea from Yerevan to Chisinau on October 1988, after the finish of the All Union Gravitational Conference held in this city is given. A Photo of the City of Yerevan during the Conference is placed: http://upmsu.phys.msu.ru/1977/gaina/Yerevan_88.jpg
NASA Astrophysics Data System (ADS)
Nagaosa, Naoto; Sinova, Jairo; Onoda, Shigeki; MacDonald, A. H.; Ong, N. P.
2010-04-01
The anomalous Hall effect (AHE) occurs in solids with broken time-reversal symmetry, typically in a ferromagnetic phase, as a consequence of spin-orbit coupling. Experimental and theoretical studies of the AHE are reviewed, focusing on recent developments that have provided a more complete framework for understanding this subtle phenomenon and have, in many instances, replaced controversy by clarity. Synergy between experimental and theoretical works, both playing a crucial role, has been at the heart of these advances. On the theoretical front, the adoption of the Berry-phase concepts has established a link between the AHE and the topological nature of the Hall currents. On the experimental front, new experimental studies of the AHE in transition metals, transition-metal oxides, spinels, pyrochlores, and metallic dilute magnetic semiconductors have established systematic trends. These two developments, in concert with first-principles electronic structure calculations, strongly favor the dominance of an intrinsic Berry-phase-related AHE mechanism in metallic ferromagnets with moderate conductivity. The intrinsic AHE can be expressed in terms of the Berry-phase curvatures and it is therefore an intrinsic quantum-mechanical property of a perfect crystal. An extrinsic mechanism, skew scattering from disorder, tends to dominate the AHE in highly conductive ferromagnets. The full modern semiclassical treatment of the AHE is reviewed which incorporates an anomalous contribution to wave-packet group velocity due to momentum-space Berry curvatures and correctly combines the roles of intrinsic and extrinsic (skew-scattering and side-jump) scattering-related mechanisms. In addition, more rigorous quantum-mechanical treatments based on the Kubo and Keldysh formalisms are reviewed, taking into account multiband effects, and demonstrate the equivalence of all three linear response theories in the metallic regime. Building on results from recent experiment and theory, a
Increase in the energy density of the pinch plasma in 3D implosion of quasi-spherical wire arrays
Aleksandrov, V. V.; Gasilov, V. A.; Grabovski, E. V.; Gritsuk, A. N. Laukhin, Ya. N.; Mitrofanov, K. N.; Oleinik, G. M.; Ol’khovskaya, O. G.; Sasorov, P. V.; Smirnov, V. P.; Frolov, I. N.; Shevel’ko, A. P.
2014-12-15
Keldysh Institute of Applied Mathematics, Russian Academy of Sciences.
Recent progress of probing correlated electron states by point contact spectroscopy.
Lee, Wei-Cheng; Greene, Laura H
2016-09-01
We review recent progress in point contact spectroscopy (PCS) to extract spectroscopic information out of correlated electron materials, with the emphasis on non-superconducting states. PCS has been used to detect bosonic excitations in normal metals, where signatures (e.g. phonons) are usually less than 1% of the measured conductance. In the superconducting state, point contact Andreev reflection (PCAR) has been widely used to study properties of the superconducting gap in various superconductors. It has been well-recognized that the corresponding conductance can be accurately fitted by the Blonder-Tinkham-Klapwijk (BTK) theory in which the AR occurring near the point contact junction is modeled by three parameters; the superconducting gap, the quasiparticle scattering rate, and a dimensionless parameter, Z, describing the strength of the potential barrier at the junction. AR can be as large as 100% of the background conductance, and only arises in the case of superconductors. In the last decade, there have been more and more experimental results suggesting that the point contact conductance could reveal new features associated with the unusual single electron dynamics in non-superconducting states, shedding a new light on exploring the nature of the competing phases in correlated materials. To correctly interpret these new features, it is crucial to re-examine the modeling of the point contact junctions, the formalism used to describe the single electron dynamics particularly in point contact spectroscopy, and the physical quantity that should be computed to understand the conductance. We will summarize the theories for point contact spectroscopy developed from different approaches and highlight these conceptual differences distinguishing point contact spectroscopy from tunneling-based probes. Moreover, we will show how the Schwinger-Kadanoff-Baym-Keldysh (SKBK) formalism together with the appropriate modeling of the nano-scale point contacts randomly distributed
First principles simulations of nanoelectronic devices
NASA Astrophysics Data System (ADS)
Maassen, Jesse
As the miniaturization of devices begins to reveal the atomic nature of materials, where chemical bonding and quantum effects are important, one must resort to a parameter-free theory for predictions. This thesis theoretically investigates the quantum transport properties of nanoelectronic devices using atomistic first principles. Our theoretical formalism employs density functional theory (DFT) in combination with Keldysh nonequilibrium Green's functions (NEGF). Self-consistently solving the DFT Hamiltonian with the NEGF charge density provides a way to simulate nonequilibrium systems without phenomenological parameters. This state-of-the-art technique was used to study three problems related to the field of nanoelectronics. First, we investigated the role of metallic contacts (Cu, Ni and Co) on the transport characteristics of graphene devices. With Cu, the graphene is simply electron-doped (Fermi level shift of ≈ -0.7 eV) which creates a unique signature in the conduction profile allowing one to extract the doping level. With Ni and Co, spin-dependent band gaps are formed in graphene's linear dispersion bands, thus leading to the prediction of high spin injection efficiencies reaching 60% and 80%, respectively. Second, we studied how controlled doping distributions in nano-scale Si transistors could suppress OFF-state leakage currents. By assuming the dopants (B and P) are confined in ≈ 1.1 nm regions in the channel, we discovered large conductance variations (GMAX/G MIN ˜ 105) as a function of the doping location. The largest fluctuations arise when the dopants are in the vicinity of the electrodes. Our results indicate that if the dopants are located away from the leads, a distance equal to 20% of the channel length, the tunneling current can be suppressed by a factor of 2 when compared to the case of uniform doping. Thus, controlled doping engineering is found to suppress device-to-device variations and lower the undesirable leakage current. Finally, we
Introduction to Nonequilibrium Statistical Mechanics with Quantum Field Theory
NASA Astrophysics Data System (ADS)
Kita, T.
2010-04-01
In this article, we present a concise and self-contained introduction to nonequilibrium statistical mechanics with quantum field theory by considering an ensemble of interacting identical bosons or fermions as an example. Readers are assumed to be familiar with the Matsubara formalism of equilibrium statistical mechanics such as Feynman diagrams, the proper self-energy, and Dyson's equation. The aims are threefold: (i) to explain the fundamentals of nonequilibrium quantum field theory as simple as possible on the basis of the knowledge of the equilibrium counterpart; (ii) to elucidate the hierarchy in describing nonequilibrium systems from Dyson's equation on the Keldysh contour to the Navier-Stokes equation in fluid mechanics via quantum transport equations and the Boltzmann equation; (iii) to derive an expression of nonequilibrium entropy that evolves with time. In stage (i), we introduce nonequilibrium Green's function and the self-energy uniquely on the round-trip Keld ysh contour, thereby avoiding possible confusions that may arise from defining multiple Green's functions at the very beginning. We try to present the Feynman rules for the perturbation expansion as simple as possible. In particular, we focus on the self-consistent perturbation expansion with the Luttinger-Ward thermodynamic functional, i.e., Baym's Phi-derivable approximation, which has a crucial property for nonequilibrium systems of obeying various conservation laws automatically. We also show how the two-particle correlations can be calculated within the Phi-derivable approximation, i.e., an issue of how to handle the ``Bogoliubov-Born-Green-Kirkwood-Yvons (BBGKY) hierarchy''. Aim (ii) is performed through successive reductions of relevant variables with the Wigner transformation, the gradient expansion based on the Groenewold-Moyal product, and Enskog's expansion from local equilibrium. This part may be helpful for convincing readers that nonequilibrium systems ca n be handled
NASA Astrophysics Data System (ADS)
Onuma, Takeyoshi; Chichibu, Shigefusa F.; Aoyama, Toyomi; Nakajima, Kiyomi; Ahmet, Parhat; Azuhata, Takashi; Chikyow, Toyohiro; Sota, Takayuki; Nagahama, Shin-ichi; Mukai, Takashi
2003-12-01
Optical and structural properties of an InGaN double-quantum-well (DQW) laser diode (LD) wafer that lased at 450 nm were investigated to discuss an enormous impact of a polarization-induced electric field on the recombination dynamics in InGaN quantum structures. The quantum-well (QW) structure was shown to have the well thickness as thin as approximately 1 nm and InN molar fraction x of approximately 14%. The gross effective electric field in the QW (FQW) was estimated to be 490 kV/cm from the Franz-Keldysh oscillation (FKO) period in the electroreflectance (ER) spectrum, implying that an internal piezoelectric field (Fpiz) of approximately 1.4 MV/cm was cancelled by the pn junction built-in field (Fbi) and Coulomb screening due to carriers in the DQW. The magnitude of FQW can be further weakened by applying reverse bias (VR) on the junction; the decrease in the photoluminescence (PL) lifetime at low temperature measured under VR was explained to be due to a recovery of electron-hole wavefunction overlap for small VR (|VR|<4 V), and due mainly to the tunneling escape of carriers through the barriers for larger VR. By applying an appropriate VR smaller than 4 V, electron-hole wavefunction overlap, which had been separated vertically along the c-axis due to quantum-confined Stark effect, could be partially recovered, and then the time-resolved PL signals exhibited a less-pronounced stretched exponential decay, giving a scaling parameter (β) of 0.85 and effective in-plane localization depth (E0) of 40-50 meV for the spontaneous emission. These values were closer to those of much homogeneous QWs compared to those reported previously for InGaN QWs having similar InN molar fractions. The use of very thin QWs is considered to bring easier Coulomb screening of FQW and population inversion under high excitation conditions.
Strong-field and attosecond physics in solids
NASA Astrophysics Data System (ADS)
Ghimire, Shambhu; Ndabashimiye, Georges; DiChiara, Anthony D.; Sistrunk, Emily; Stockman, Mark I.; Agostini, Pierre; DiMauro, Louis F.; Reis, David A.
2014-10-01
We review the status of strong-field and attosecond processes in bulk transparent solids near the Keldysh tunneling limit. For high enough fields and low-frequency excitations, the optical and electronic properties of dielectrics can be transiently and reversibly modified within the applied pulse. In Ghimire et al (2011 Phys. Rev. Lett. 107 167407) non-parabolic band effects were seen in photon-assisted tunneling experiments in ZnO crystals in a strong mid-infrared field. Using the same ZnO crystals, Ghimire et al (2011 Nat. Phys. 7 138-41) reported the first observation of non-pertubative high harmonics, extending well above the bandgap into the vacuum ultraviolet. Recent experiments by Schubert et al (2014 Nat. Photonics 8 119-23) showed a carrier envelope phase dependence in the harmonic spectrum in strong-field 30 THz driven GaSe crystals which is the most direct evidence yet of the role of sub-cycle electron dynamics in solid-state harmonic generation. The harmonic generation mechanism is different from the gas phase owing to the high density and periodicity of the crystal. For example, this results in a linear dependence of the high-energy cutoff with the applied field in contrast to the quadratic dependence in the gas phase. Sub-100 attosecond pulses could become possible if the harmonic spectrum can be extended into the extreme ultraviolet (XUV). Here we report harmonics generated in bulk MgO crystals, extending to ˜ 26 eV when driven by ˜35 fs, 800 nm pulses focused to a ˜1 VÅ-1 peak field. The fundamental strong-field and attosecond response also leads to Wannier-Stark localization and reversible semimetallization as seen in the sub-optical cycle behavior of XUV absorption and photocurrent experiments on fused silica by Schiffrin et al (2013 Nature 493 70-4) and Schultze et al (2013 Nature 493 75-8). These studies are advancing our understanding of fundamental strong-field and attosecond physics in solids with potential applications for compact
Bulk Laser Material Modification: Towards a Kerfless Laser Wafering Process
NASA Astrophysics Data System (ADS)
LeBeau, James
Due to the ever increasing relevance of finer machining control as well as necessary reduction in material waste by large area semiconductor device manufacturers, a novel bulk laser machining method was investigated. Because the cost of silicon and sapphire substrates are limiting to the reduction in cost of devices in both the light emitting diode (LED) and solar industries, and the present substrate wafering process results in >50% waste, the need for an improved ingot wafering technique exists. The focus of this work is the design and understanding of a novel semiconductor wafering technique that utilizes the nonlinear absorption properties of band-gapped materials to achieve bulk (subsurface) morphological changes in matter using highly focused laser light. A method and tool was designed and developed to form controlled damage regions in the bulk of a crystalline sapphire wafer leaving the surfaces unaltered. The controllability of the subsurface damage geometry was investigated, and the effect of numerical aperture of the focusing optic, energy per pulse, wavelength, and number of pulses was characterized for a nanosecond pulse length variable wavelength Nd:YAG OPO laser. A novel model was developed to describe the geometry of laser induced morphological changes in the bulk of semiconducting materials for nanosecond pulse lengths. The beam propagation aspect of the model was based on ray-optics, and the full Keldysh multiphoton photoionization theory in conjuncture with Thornber's and Drude's models for impact ionization were used to describe high fluence laser light absorption and carrier generation ultimately resulting in permanent material modification though strong electron-plasma absorption and plasma melting. Although the electron-plasma description of laser damage formation is usually reserved for extremely short laser pulses (<20 ps), this work shows that it can be adapted for longer pulses of up to tens of nanoseconds. In addition to a model
SymGF: A Symbolic Tool for Quantum Transport Theory
NASA Astrophysics Data System (ADS)
Feng, Zi Min
In this thesis, I report the development and application of a symbolic derivation tool named "SymGF'' - standing for Symbolic Green's Function, that can automatically and analytically derive quantum transport expressions and the associated Keldysh nonequilibrium Green's functions (NEGF). Quantum transport happens in open systems consisting of a scattering region coupled to external electrodes. When there are strong electron-electron interactions in the scattering region, analytical derivations of the Green's functions can be very tedious and error prone. Running on a personal computer, SymGF derives the necessary analytical formulas at a level of correlation specified by the user, using the equation of motion (EOM) method. The input to SymGF are the second quantized form the device Hamiltonian, the (anti)commutators of the operators that appear in the Hamiltonian, and a truncation rule for the correlators which determines the accuracy of the final outcome. The output of SymGF are the analytical expressions of transport properties such as electric current and conductance in terms of various Green's functions; as well as the Green's functions themselves in terms of the unperturbed non-interacting Green's functions that can be obtained straightforwardly. For systems where electron-electron interaction can be neglected, the transport problems can be easily solved and SymGF is not necessary - even though SymGF gives the same answer; but for interacting systems SymGF drastically reduces the mathematical burden of analytical derivations. We have tested SymGF for several transport problems involving Kondo resonances where analytical derivations were done by humans: exactly the same results were obtained by SymGF but in a tiny fraction of time. We have applied SymGF to new and very hard problems that resist analytical derivations by hand, including quantum transport in a double quantum dot system; transport through a single quantum dot in parallel to a direct lead
Non equilibrium electronic transport in multilayered nanostructures
NASA Astrophysics Data System (ADS)
Cruz-Rojas, Jesus
Recent advances in strongly correlated materials have produced systems with novel and interesting properties like high Tc superconductors, Mott insulators and others. These novel properties have sparked an interest in industry as well as in academia as new devices are being developed. One such kind of device that can be fabricated is a heterostructure, in which layers of different compounds are stacked in a single direction. Modern deposition techniques like electron beam epitaxy, in which atomic layers of different materials are deposited one at a time creating the device, are capable of fabricating heterostructures with atomic precision. We propose a technique to study heterostructures composed of strongly correlated materials out of equilibrium. By using the Keldysh Green's function formalism in the dynamical mean field theory (DMFT) framework the properties of a multilayered device are analyzed. The system is composed of infinite dimensional 2D lattices, stacked in the z direction. The first and last planes are then connected to a bulk reservoir, and several metallic planes are used to connect the bulk reservoir to the barrier region. The barrier region is the system of interest, also known as the device. The device is composed of a number of planes where the system correlations have been turned on. The correlations are then model by using the Falicov-Kimball Hamiltonian. The device is then connected to the bulk once again from the opposite side using metallic planes creating a symmetric system. In order to study the non equilibrium properties of the device a linear vector potential A(t) = A0 + tE is turned on a long time in the past for a unit of time and then turned off. This in turn will create a current in the bulk, in effect current biasing the device, as opposed to a voltage bias in which opposite sides of the device are held to a different potential. In this document we will explain the importance of the subject, we will derive and develop the algorithm
Recent progress of probing correlated electron states by point contact spectroscopy
NASA Astrophysics Data System (ADS)
Lee, Wei-Cheng; Greene, Laura H.
2016-09-01
We review recent progress in point contact spectroscopy (PCS) to extract spectroscopic information out of correlated electron materials, with the emphasis on non-superconducting states. PCS has been used to detect bosonic excitations in normal metals, where signatures (e.g. phonons) are usually less than 1% of the measured conductance. In the superconducting state, point contact Andreev reflection (PCAR) has been widely used to study properties of the superconducting gap in various superconductors. It has been well-recognized that the corresponding conductance can be accurately fitted by the Blonder-Tinkham-Klapwijk (BTK) theory in which the AR occurring near the point contact junction is modeled by three parameters; the superconducting gap, the quasiparticle scattering rate, and a dimensionless parameter, Z, describing the strength of the potential barrier at the junction. AR can be as large as 100% of the background conductance, and only arises in the case of superconductors. In the last decade, there have been more and more experimental results suggesting that the point contact conductance could reveal new features associated with the unusual single electron dynamics in non-superconducting states, shedding a new light on exploring the nature of the competing phases in correlated materials. To correctly interpret these new features, it is crucial to re-examine the modeling of the point contact junctions, the formalism used to describe the single electron dynamics particularly in point contact spectroscopy, and the physical quantity that should be computed to understand the conductance. We will summarize the theories for point contact spectroscopy developed from different approaches and highlight these conceptual differences distinguishing point contact spectroscopy from tunneling-based probes. Moreover, we will show how the Schwinger-Kadanoff-Baym-Keldysh (SKBK) formalism together with the appropriate modeling of the nano-scale point contacts randomly distributed
Ramzaev, V; Nikitin, A; Sevastyanov, A; Artemiev, G; Bruk, G; Ivanov, S
2014-09-01
A total of 88 seawater samples were collected during two Russian research expeditions (April-May 2011 and August-September 2012) to the Sea of Japan, the Oyashio Current region near Kuril Islands and the Kuroshio-Oyashio transition area in the western North Pacific Ocean. The observations were made aboard the R/V Pavel Gordienko and Akademik Shokalsky in order to study the impact of the Fukushima accident on radioactive contamination of the marine environment. On the board of a ship, the water samples were passed through filters to retain particles with the size of >1 micron. Cesium was extracted from the large volumes (100-3000 L) of the filtrated water using a selective fiber chemisorbent impregnated with copper ferrocyanide. Measurements of (134)Cs and (137)Cs activities in 83 samples of sorbents and 21 samples of filters were performed in the ship-based laboratory with a semiconductor HP-Ge detector. The quantified activity concentrations of dissolved radiocesium ranged from 1 Bq m(-3) to 34 Bq m(-3) for (137)Cs and from 0.2 Bq m(-3) to 29 Bq m(-3) for (134)Cs. Activity concentrations of (137)Cs and (134)Cs were strongly correlated with each other (r = 0.993, n = 59). The (137)Cs/(134)Cs activities ratio in the Fukushima-derived radiocesium inventory for the study areas was deduced to be 0.99 ± 0.03 (on 15 March 2011) and the pre-Fukushima background level of (137)Cs in seawater was estimated as 1.3 ± 0.3 Bq m(-3). The lowest activities of both isotopes were determined in the western part of the Sea of Japan near the Russian coast, while the maximal levels were observed in the open Pacific Ocean, some 500-800 km offshore the Fukushima Dai-ichi Nuclear Power Plant. Contamination with (134)Cs at a level of 0.3-2.6 Bq m(-3) was registered in seawater samples collected in 2011 near the Kuril Islands and Kamchatka in the Oyashio Current region. During the period from April-May 2011 to August-September 2012, activity concentrations of (137)Cs and (134)Cs in surface
Origin of variolitic lavas: Evidence for variolites in axial part of the Mid-Atlantic Ridge, 6oN
NASA Astrophysics Data System (ADS)
Sharkov, Evgenii; Krssivskaya, Irina; Chistyakov, Alexei
2010-05-01
Fragment of variolitic lavas was dredged in axial part of the MAR at 6oN during 10th cruise of R/V "Akademik Ioffe" (2001-2002). It is rock where rounded globules of andesite (icelandite) with light trachyandesite rims are enclosed in high-Ti picrobasalt matrix. The sample can be subdivided in two different structural parts, or "layers". One of them densely saturated by globules, which closely adjoin to each other, merge in clumpy congregations with small quantity of matrix material in interstices. In the other part of the sample matrix predominates. Isolated, sometimes sticked together globules "swim" in the matrix and their quantity and size quickly decrease to the sample edge, where only small rare globules occur. Boundary between both parts, even if irregular due to rounded shape of closed globules, nevertheless is well-defined and has small bays of the matrix material. So, globules were moved in picrobasalt melt and floated up to the surface of the lava flow. It is shown that formation of the leucocratic rims was evidently linked with thermal diffusion phenomenon (Soret principle) in cooling heterogeneous melt. According to this principle, components in solutions and melts, placed in thermal gradient, are redistributed for leveling of internal energy in that way, when light elements migrate to hot parts and heavy ones to cold. Experimental studies of thermal diffusion in samples of MORB showed enlarge of Si, Al, Na and K concentration to side of hot area of melt and Fe, Mg, Ca, etc. to cold one; resulting melts were Qtz-normative andesites and Ne-normative picrite (Walker, DeLong, 1982). The same picture we saw in our sample: enrichment of external zone of globules by Si, Al, and, especially, by high-mobile Na, which diffusion rate in silicate melts in some order higher than speed of remaining elements (Watson, 1982; Borisov, 2008). Simultaneously, this zone impoverished by Fe, Ca and Mg, which were concentrated in rear of rims, forming internal zoning of
NASA Astrophysics Data System (ADS)
Sharkov, E. V.
2010-12-01
Fragment of variolitic lavas was dredged in axial part of the MAR at 6oN during 10th cruise of R/V “Akademik Ioffe” (2001-2002). It is rock where rounded globules of andesite (icelandite) with light trachyandesite rims are enclosed in Fe-Ti picrobasalt matrix. The sample can be subdivided in two different structural parts or “layers”. One of them densely saturated by globules, which closely adjoin to each other, merge in clumpy congregations; in another part matrix predominates. Boundary between both parts, even if irregular due to rounded shape of closed globules, nevertheless is well-defined and has small bays of the matrix material. So, globules were moved in picrobasaltic melt and floated up to the surface of the lava flow. It is shown that formation of the leucocratic rims was evidently linked with thermal diffusion phenomenon (Soret principle) in cooling heterogeneous melt. According to this principle, components in solutions and melts, placed in thermal gradient, are redistributed for leveling of internal energy in that way, when light elements migrate to hot parts and heavy ones to cold. Experimental studies of thermal diffusion in samples of MORB showed enlarge of Si, Al, Na and K concentration to side of hot area of melt and Fe, Mg, Ca, etc. to cold one; resulting melts were andesites and Ne-normative picrite (Walker, DeLong, 1982). The same picture we saw in our sample: enrichment of external zone of globules by Si, Al, and, especially, by high-mobile Na, which diffusion rate in silicate melts in some order higher than speed of remaining elements (Watson, 1982; Borisov, 2008). Simultaneously, this zone impoverished by Fe, Ca and Mg, which were concentrated in rear of rims, forming internal zoning of globules with careless boundaries. Effect of thermal diffusion in more important for Fe; as a result #mg in trachyandesite rims higher than in andesite cores of globules. It suggests that origin of variolites was linked with intersection by ascended
NASA Astrophysics Data System (ADS)
Roque, C.; Simões, M.; Lourenço, N.; Pinto de Abreu, M.
2009-04-01
The West Madeira Abyssal Plain is located in the eastern North Atlantic off Madeira Islands, forming part of the Canary Basin and reaching a mean water depth of 5300 m. This region is also located within Africa plate at about 500 km southwards from the Açores-Gibraltar plate boundary, and for that reason lacks seismic activity. Although this region being located in an intraplate setting, the presence of faulted sediments was reported in several works published during the eighties of last century following a study conducted in late 1970s to evaluate the feasibility of disposal of high-level radioactive wastes in the ocean. According these works, the Madeira Abyssal Plain sediments are cut by many normal growth faults and this deformation is a result of compaction and dewatering of the sediments. Evidences of tectonic deformation of oceanic sediments in intraplate settings are uncommon, but folded sediments and reverse faults extending into the basement, were recognized in the equatorial Indian Ocean and in the West African continental margin. Recently, during 2006 multi-channel seismic reflection and multibeam swath bathymetry surveys were carried out in the West Madeira Abyssal Plain by EMEPC in order to prepare the Portuguese proposal for the extension of the continental shelf. The seismic lines were acquired onboard R/V Akademik Shatskiy using a source of 5720 cu in bolt gun array, cable length of 7950 m and shot interval of 50.00 m. The multibeam swath bathymetry was acquired onboard NRP Gago Coutinho, and allowed a high resolution mapping of the main geomorphological features. The multichannel seismic lines, oriented WNW-ESE, image the Madeira island lower slope located at about 4000 m water depth and the almost flat abyssal plain at about 5300 m water depth. These seismic lines show a thick sedimentary succession that reaches a maximum thickness of about 1.5 sec twt in the deepest parts of the West Madeira Abyssal Plain, overlying an irregular diffractive
Giant mudwaves in the Northern Argentine Basin: born and buried by bottom currents
NASA Astrophysics Data System (ADS)
Borisov, Dmitrii; Murdmaa, Ivar; Ivanova, Elena; Levchenko, Oleg
2014-05-01
New sedimentary records and very high resolution seismic profiles collected during four cruises of the RV "Akademik Ioffe" (2011-2013) were correlated with seismic, multibeam and coring data obtained during cruises of the RV "Robert Conrad", "Knorr", "Meteor". A complex analysis of the geological-geophysical data revealed an extensive field of giant mudwaves (48 000 km2) in the northwestern Argentine Basin, South Atlantic. The symmetric waves up to 60 m in height and 4000 m in wavelength are oriented roughly parallel to contours. They partly cover the Santa Catarina Plateau and extend through the Santos Basin to the Sao Paulo Plateau. The mudwaves field is traced at the depth range from 3400 to 4000 m and divided into buried (northern) and non-buried (southern) parts. The non-buried sediment waves cover the surface of the huge drift in the Santa Catarina Plateau. The wave height increases from the drift summit to its flanks and decreases at the foot. Two cores retrieved from the drift top and its northern flank recovered muddy contourites with a greater amount of silt-size material in the core from the drift flank. The age of the recovered sediments is at least 130 ka. In the northern Santos basin, the sediment waves are buried under a large lens-like sediment body (drift?) inclined at the margins. Cores obtained from the buried part of the mudwaves field recovered an intercalation of hemipelagic clay and silty-clay contourite. The age of recovered sediments does not exceed 150 ka (Bleil et al., 1993). Contourites deposition in the study area is related to the activity of the Antarctic bottom water (AABW) contour current. The AABW flow is considered to be divided into two branches by the Santa Catarina Plateau. We suggest that this topographic obstacle causes a flow velocity increase. Wave height and grain-size variations indicate higher bottom current velocities at the plateau flanks and relative tranquil conditions at the flat summit of the plateau. The symmetric
NASA Astrophysics Data System (ADS)
Mahfouzi, Farzad
ferromagnet (FM). I show that this could be due to the existence of Rashba spin-orbit coupling (SOC) at the interface of the FM and insulator. Assuming that the measured signals are quantum mechanical effect where a solution to the time dependent Schrodinger equation is required, I use Keldysh Green function formalism to introduce a "multi-photon" approach which takes into account the effects of time-dependent term exactly up to scatterings from a finite number of photons. We then proceed to find the corresponding Green function numerically using a recursive method which allows us to increase the size of the system significantly. We also implement other approximations such as adiabatic and rotating frame approaches and compared them with our approach. In Chapter 4, I investigate the spin and charge pumping from a precessing magnetization attached to the edge of a 2-dimensional topological insulator (2DTI). We show that, in this system a huge spin current (or voltage signal if the FM covers only one edge) can be pumped for very small cone angles of the precessing FM (proportional to the intensity of the applied microwave). In Chapter 5 I present the third project in this field of research, where, I investigated the pumping from FM attached to a 3-dimensional TI. Spin-transfer torque: Presented in Chapter 6, in this work I investigate the torque induced by a flow of spin-polarized current into a FM and check the condition in which it can cause the magnetization to flip. Motivated by recent experimental developments in the field, here I consider systems with strong SOC such as TIs within a magnetic tunnel junction (MTJ) heterostructure. In the theoretical part I show the correct way (as opposed to the conventional approach used in some theoretical works which suffers from violation of the gauge invariance) to calculate linear-response torque to the external applied voltage and for the numerical calculation I adopted a parallelized adaptive integration algorithm in order to take
The behaviour of cloud and clear sky brightness in the vicinity of the cloud edge
NASA Astrophysics Data System (ADS)
Bass, L.; Nikolaeva, O.; Kuznetsov, V.; Kokhanovsky, A.
2007-12-01
L.P. Bass1, O.V. Nikolaeva1, V.S.Kuznetsov2, A. A. Kokhanovsky3,4 1Keldysh Institute of Applied Mathematics, Russian Academy of Science Miusskaya Sq. 4,125047 Moscow, Russia 2Research Scientific Center "Kurchatov Institute", Kurchatov Sq. 1, 123182 Moscow, Russia 3Institute of Remote Sensing, Bremen University, Otto Hahn Allee 1 28334 Bremen, Germany 4Institute of Physics, National Academy of Sciences of Belarus, Nezaleznasti Pr. 70 220072 Minsk, Belarus In the solution of remote sensing problems in the framework of the Independent Pixel Approximation (IPA) the horizontal transport of radiation is not taken into account. Therefore, the large errors in the retrieved optical parameters of a medium under study can occur in retrievals for regions, where 3-D radiative transfer effects are of importance (Wen et al, 2007, Titov, 1998). In the present work we analyze the brightness at the edge of a cubic cloud. The energy balance equations within the clear sky-cloud boundary layer are studied. The boundary layer is the domain that includes the vertical boundary of the adjacent pixels with different optical properties. Balance equation connects the radiation fluxes entering into the boundary layer and outgoing from it, and also the amount of energy absorbed in the layer. It is demonstrated that horizontal transport of radiation generates several observable phenomena such as "shadowing" and "brightening" (depending on the Sun position with respect to the cloud and also the area studied). All calculations are performed with the code Raduga-5.1 (Nikolaeva et al., 2005) developed for the computer with the parallel architecture for 1-D, 2-D, 3-D radiative transfer. The code is based on the numerical solution of the integro - differential radiative transfer equation (RTE) with correspondent boundary conditions and prescribed properties of a light scattering medium. Grids with respect to spatial and angular variables are introduced and RTE reduced to the system of the grid
PREFACE: Ultrafast and nonlinear optics in carbon nanomaterials
NASA Astrophysics Data System (ADS)
Kono, Junichiro
2013-02-01
Carbon-based nanomaterials—single-wall carbon nanotubes (SWCNTs) and graphene, in particular—have emerged in the last decade as novel low-dimensional systems with extraordinary properties. Because they are direct-bandgap systems, SWCNTs are one of the leading candidates to unify electronic and optical functions in nanoscale circuitry; their diameter-dependent bandgaps can be utilized for multi-wavelength devices. Graphene's ultrahigh carrier mobilities are promising for high-frequency electronic devices, while, at the same time, it is predicted to have ideal properties for terahertz generation and detection due to its unique zero-gap, zero-mass band structure. There have been a large number of basic optical studies on these materials, but most of them were performed in the weak-excitation, quasi-equilibrium regime. In order to probe and assess their performance characteristics as optoelectronic materials under device-operating conditions, it is crucial to strongly drive them and examine their optical properties in highly non-equilibrium situations and with ultrashot time resolution. In this section, the reader will find the latest results in this rapidly growing field of research. We have assembled contributions from some of the leading experts in ultrafast and nonlinear optical spectroscopy of carbon-based nanomaterials. Specific topics featured include: thermalization, cooling, and recombination dynamics of photo-generated carriers; stimulated emission, gain, and amplification; ultrafast photoluminescence; coherent phonon dynamics; exciton-phonon and exciton-plasmon interactions; exciton-exciton annihilation and Auger processes; spontaneous and stimulated emission of terahertz radiation; four-wave mixing and harmonic generation; ultrafast photocurrents; the AC Stark and Franz-Keldysh effects; and non-perturbative light-mater coupling. We would like to express our sincere thanks to those who contributed their latest results to this special section, and the
First Principles Quantitative Modeling of Molecular Devices
NASA Astrophysics Data System (ADS)
Ning, Zhanyu
In this thesis, we report theoretical investigations of nonlinear and nonequilibrium quantum electronic transport properties of molecular transport junctions from atomistic first principles. The aim is to seek not only qualitative but also quantitative understanding of the corresponding experimental data. At present, the challenges to quantitative theoretical work in molecular electronics include two most important questions: (i) what is the proper atomic model for the experimental devices? (ii) how to accurately determine quantum transport properties without any phenomenological parameters? Our research is centered on these questions. We have systematically calculated atomic structures of the molecular transport junctions by performing total energy structural relaxation using density functional theory (DFT). Our quantum transport calculations were carried out by implementing DFT within the framework of Keldysh non-equilibrium Green's functions (NEGF). The calculated data are directly compared with the corresponding experimental measurements. Our general conclusion is that quantitative comparison with experimental data can be made if the device contacts are correctly determined. We calculated properties of nonequilibrium spin injection from Ni contacts to octane-thiolate films which form a molecular spintronic system. The first principles results allow us to establish a clear physical picture of how spins are injected from the Ni contacts through the Ni-molecule linkage to the molecule, why tunnel magnetoresistance is rapidly reduced by the applied bias in an asymmetric manner, and to what extent ab initio transport theory can make quantitative comparisons to the corresponding experimental data. We found that extremely careful sampling of the two-dimensional Brillouin zone of the Ni surface is crucial for accurate results in such a spintronic system. We investigated the role of contact formation and its resulting structures to quantum transport in several molecular
Strongly correlated quantum transport out-of-equilibrium
NASA Astrophysics Data System (ADS)
Dutt, Prasenjit
The revolutionary advances in nanotechnology and nanofabrication have facilitated the precise control and manipulation of mesoscopic systems where quantum effects are pronounced. Quantum devices with tunable gates have made it possible to access regimes far beyond the purview of linear response theory. In particular, the influence of strong voltage and thermal biases has led to the observation of novel phenomena where the non-equilibrium characteristics of the system are of paramount importance. We study transport through quantum-impurity systems in the regime of strong correlations and determine the effects of large temperature and potential gradients on its many-body physics. In Part I of this thesis we focus on the steady-state dynamics of the system, a commonly encountered experimental scenario. For a system consisting of several leads composed of non-interacting electrons, each individually coupled to a quantum impurity with interactions and maintained at different chemical potentials, we reformulate the system in terms of an effective-equilibrium density matrix. This density matrix has a simple Boltzmann-like form in terms of the system's Lippmann-Schwinger (scattering) operators. We elaborate the conditions for this description to be valid based on the microscopic Hamiltonian of the system. We then prove the equivalence of physical observables computed using this formulation with corresponding expressions in the Schwinger-Keldysh approach and provide a dictionary between Green's functions in either scheme. An imaginary-time functional integral framework to compute finite temperature Green's functions is proposed and used to develop a novel perturbative expansion in the interaction strength which is exact in all other system parameters. We use these tools to study the fate of the Abrikosov-Suhl regime on the Kondo-correlated quantum dot due to the effects of bias and external magnetic fields. Next, we expand the domain of this formalism to additionally
NASA Astrophysics Data System (ADS)
2014-02-01
On 5 - 6 June 2013, an extended session of the all-institute seminar was held at the Russian Federation State Scientific Center 'Alikhanov Institute for Theoretical and Experimental Physics' (ITEP). It was devoted to the 100th anniversary of the birth of Academician Isaak Yakovlevich Pomeranchuk, the founder of the Theory Department of ITEP. The announced agenda of the session on the ITEP website http://www.itep.ru/rus/Pomeranchuk100.html contained the following reports: (1) Gershtein S S (SRC 'Institute for High Energy Physics', Protvino, Moscow region) "I Ya Pomeranchuk and the large accelerator";(2) Keldysh L V (Lebedev Physical Institute, RAS (FIAN), Moscow) "Dynamic tunneling";(3) Vaks V G (National Research Centre 'Kurchatov Institute' (NRC KI), Moscow) "Brief reminiscences";(4) Smilga A V (Laboratoire Physique Subatomique et des technologies associées, Université de Nantes, France) "Vacuum structure in 3D supersymmetric gauge theories";(5) Khriplovich I B (Budker Institute of Nuclear Physics, SB RAS, Novosibirsk) "Gravitational four-fermion interaction and early Universe dynamics";(6) Dremin I M (FIAN, Moscow) "Elastic scattering of hadrons";(7) Belavin A A (Landau Institute of Theoretical Physics, RAS, Moscow) "Correlators in minimal string models";(8) Voloshin M B (Theoretical Physics Institute, University of Minnesota, USA) "Exotic quarkonium";(9) Nekrasov N A (Institut des hautes études scientifiques (IHES), France) "BPS/CFT correspondence";(10) Zarembo K (Uppsala Universitet, Sweden) "Exact results in supersymmetric theories and AdS/CFT correspondence";(11) Gorsky A S (ITEP, Moscow) "Baryon as a dyon instanton";(12) Blinnikov S I (ITEP, Moscow) "Mirror substance and other models for dark matter";(13) Rubakov V A (Institute for Nuclear Research, RAS, Moscow) "Test-tube Universe";(14) Kancheli O V (ITEP, Moscow) "50 years of reggistics";(15) Shevchenko V I (NRC KI) "In search of the chiral magnetic effect";(16) Kirilin V P (ITEP, Moscow) "Anomalies and
Alidoust, Mohammad; Halterman, Klaus
2015-03-28
Using a spin-parameterized quasiclassical Keldysh-Usadel technique, we theoretically study supercurrent transport in several types of diffusive ferromagnetic (F)/superconducting (S) configurations with differing magnetization textures. We separate out the even- and odd-frequency components of the supercurrent within the low proximity limit and identify the relative contributions from the singlet and triplet channels. We first consider inhomogeneous one-dimensional Josephson structures consisting of a uniform bilayer magnetic S/F/F/S structure and a trilayer S/F/F/F/S configuration, in which case the outer F layers can have either a uniform or conical texture relative to the central uniform F layer. Our results demonstrate that for supercurrents flowing perpendicular to the F/F interfaces, incorporating a conical texture yields the most effective way to observe the signatures of long-ranged spin-triplet supercurrents. We also consider three different types of finite-sized two-dimensional magnetic structures subjected to an applied magnetic field normal to the junction plane: a S/F/S junction with uniform magnetization texture and two S/F/F/S configurations with differing F/F bilayer arrangements. In one case, the F/F interface is parallel with the S/F junction interfaces while in the other case, the F/F junction is oriented perpendicular to the S/F interfaces. We then discuss the proximity vortices and corresponding spatial maps of currents inside the junctions. For the uniform S/F/S junction, we analytically calculate the magnetic field induced supercurrent and pair potential in both the narrow and wide junction regimes, thus providing insight into the variations in the Fraunhofer diffraction patterns and proximity vortices when transitioning from a wide junction to a narrow one. Our extensive computations demonstrate that the induced long-range spin-triplet supercurrents can deeply penetrate uniform F/F bilayers when spin-singlet supercurrents flow parallel to the
NASA Astrophysics Data System (ADS)
Mahfouzi, Farzad; Nikolić, Branislav K.
2014-07-01
We develop a numerically exact scheme for resumming certain classes of Feynman diagrams in the self-consistent perturbative expansion for the electron and magnon self-energies in the nonequilibrium Green function formalism applied to a coupled electron-magnon (e-m) system driven out of equilibrium by the applied finite bias voltage. Our scheme operates with the electronic and magnonic GFs and the corresponding self-energies viewed as matrices in the Keldysh space, rather than conventionally extracting their retarded and lesser components, which greatly simplifies translation of diagrams into compact mathematical expressions and their computational implementation. This is employed to understand the effect of inelastic e-m scattering on charge and spin current vs bias voltage Vb in F/I/F (F-ferromagnet; I-insulating barrier) magnetic tunnel junctions (MTJs), which are modeled on a quasi-one-dimensional (quasi-1D) tight-binding lattice for the electronic subsystem and quasi-1D Heisenberg model for the magnonic subsystem. For this purpose, we evaluate the Fock diagram for the electronic self-energy and the electron-hole polarization bubble diagram for the magnonic self-energy. The respective electronic and magnonic GF lines within these diagrams are the fully interacting ones, thereby requiring to solve the ensuing coupled system of nonlinear integral equations self-consistently. Despite using the quasi-1D model and treating e-m interaction in many-body fashion only within a small active region consisting of few lattice sites around the F/I interface, our analysis captures essential features of the so-called zero-bias anomaly observed [V. Drewello, J. Schmalhorst, A. Thomas, and G. Reiss, Phys. Rev. B 77, 014440 (2008), 10.1103/PhysRevB.77.014440] in both MgO- and AlOx-based realistic 3D MTJs where the second derivative d2I /dVb2 (i.e., inelastic electron tunneling spectrum) of charge current exhibits sharp peaks of opposite sign on either side Vb=0. We show that this
NASA Astrophysics Data System (ADS)
2014-02-01
On 5 - 6 June 2013, an extended session of the all-institute seminar was held at the Russian Federation State Scientific Center 'Alikhanov Institute for Theoretical and Experimental Physics' (ITEP). It was devoted to the 100th anniversary of the birth of Academician Isaak Yakovlevich Pomeranchuk, the founder of the Theory Department of ITEP. The announced agenda of the session on the ITEP website http://www.itep.ru/rus/Pomeranchuk100.html contained the following reports: (1) Gershtein S S (SRC 'Institute for High Energy Physics', Protvino, Moscow region) "I Ya Pomeranchuk and the large accelerator";(2) Keldysh L V (Lebedev Physical Institute, RAS (FIAN), Moscow) "Dynamic tunneling";(3) Vaks V G (National Research Centre 'Kurchatov Institute' (NRC KI), Moscow) "Brief reminiscences";(4) Smilga A V (Laboratoire Physique Subatomique et des technologies associées, Université de Nantes, France) "Vacuum structure in 3D supersymmetric gauge theories";(5) Khriplovich I B (Budker Institute of Nuclear Physics, SB RAS, Novosibirsk) "Gravitational four-fermion interaction and early Universe dynamics";(6) Dremin I M (FIAN, Moscow) "Elastic scattering of hadrons";(7) Belavin A A (Landau Institute of Theoretical Physics, RAS, Moscow) "Correlators in minimal string models";(8) Voloshin M B (Theoretical Physics Institute, University of Minnesota, USA) "Exotic quarkonium";(9) Nekrasov N A (Institut des hautes études scientifiques (IHES), France) "BPS/CFT correspondence";(10) Zarembo K (Uppsala Universitet, Sweden) "Exact results in supersymmetric theories and AdS/CFT correspondence";(11) Gorsky A S (ITEP, Moscow) "Baryon as a dyon instanton";(12) Blinnikov S I (ITEP, Moscow) "Mirror substance and other models for dark matter";(13) Rubakov V A (Institute for Nuclear Research, RAS, Moscow) "Test-tube Universe";(14) Kancheli O V (ITEP, Moscow) "50 years of reggistics";(15) Shevchenko V I (NRC KI) "In search of the chiral magnetic effect";(16) Kirilin V P (ITEP, Moscow) "Anomalies and
Fluidodynamic Processes in Different Regimes of Dilotansy and Compaction
NASA Astrophysics Data System (ADS)
Dmitrievsky, A. N.; Balanyuk, I. E.; Karakin, A. V.; Poveschenko, Yu. A.; Dongaryan, L. Sh.
2003-04-01
FLUIDODYNAMIC PROCESS IN DIFFERENT REGIMES OF DILOTANSY AND COMPACTION A. N. Dmitrievsky(1), I. E. Balanyuk(2), A. V.Karakin, (3), Yu. A. Poveschenko(4), L.Sh. Dongaryan(2) (1) Institute of Oil and Gas Problems, (2) P.P. Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia, balanyuk@sio.rssi.ru, (3)VNIIGeosystem, Moscow, Russia, (4) Keldysh Institute of Applied Mathematics Russian Academy of Sciences, Moscow. The proposed crust waveguide model features versatility and enables to clarify the weakest elements in presently accepted visions of migration mechanisms and hydrocarbon fluid accumulations. The model of the crust waveguide is based on the following considerations. Horizontal tectonic stress is always present in the crust, causing shifts of layers relative to each other. When shear strains develop in a fractured layer, dilatant expansion occurs and is accompanied by increases in pore volume in the layer. This leads to pore pressure drops and suction of fluids into the expanding volume. In particular, those fluids are sucked which are present in the surface layers. They move through faulted and fractured zones downward, and reach the middle crust depths. This effect is basically known and is identified in geophysical literature as "tectonic pumping". At a certain moment, dilatant expansion is replaced by compression, and this process can be described by socalled compaction equations. Cyclic alteration of these regimes in the crust waveguide will finally ensure its dynamic equilibrium. The unbalanced processes in the middle crust leads to important geophysical implications. The crust waveguide located at 10 - 15 km depths acts as a pump. Water flows, which rush downward, are "washing up" the upper crust layers, dissolving and entraining mineral and organic materials. During the squeezing of fluids from the crust waveguide, these dissolved materials are concentrating and forming corresponding ore and hydrocarbon deposits in the upper
NASA Astrophysics Data System (ADS)
Mahfouzi, Farzad
ferromagnet (FM). I show that this could be due to the existence of Rashba spin-orbit coupling (SOC) at the interface of the FM and insulator. Assuming that the measured signals are quantum mechanical effect where a solution to the time dependent Schrodinger equation is required, I use Keldysh Green function formalism to introduce a "multi-photon" approach which takes into account the effects of time-dependent term exactly up to scatterings from a finite number of photons. We then proceed to find the corresponding Green function numerically using a recursive method which allows us to increase the size of the system significantly. We also implement other approximations such as adiabatic and rotating frame approaches and compared them with our approach. In Chapter 4, I investigate the spin and charge pumping from a precessing magnetization attached to the edge of a 2-dimensional topological insulator (2DTI). We show that, in this system a huge spin current (or voltage signal if the FM covers only one edge) can be pumped for very small cone angles of the precessing FM (proportional to the intensity of the applied microwave). In Chapter 5 I present the third project in this field of research, where, I investigated the pumping from FM attached to a 3-dimensional TI. Spin-transfer torque: Presented in Chapter 6, in this work I investigate the torque induced by a flow of spin-polarized current into a FM and check the condition in which it can cause the magnetization to flip. Motivated by recent experimental developments in the field, here I consider systems with strong SOC such as TIs within a magnetic tunnel junction (MTJ) heterostructure. In the theoretical part I show the correct way (as opposed to the conventional approach used in some theoretical works which suffers from violation of the gauge invariance) to calculate linear-response torque to the external applied voltage and for the numerical calculation I adopted a parallelized adaptive integration algorithm in order to take
Some Unknown Pages of the Living Organisms' First Orbital Flight
NASA Astrophysics Data System (ADS)
Malashenkov, D. C.
2002-01-01
The successful creation of ballistic rockets in USSR has allowed at the end of 1953 to make a real task of delivery of a payload into the Earth's orbit. In March 1954 during the meeting in the Academy of Sciences of USSR, the basic research problems conducted by means of artificial satellites of the Earth were determined. In May, 1954 S. Korolev has sent to Government of the USSR the report with the offer of creation the space satellites on the basis of intercontinental ballistic rocket -7 developed by him. It was the first time when the idea about possibility of interplanetary flights was stated in the official document. In August 1954 Council of Ministers of the USSR had ratified the submitted offers and have entrusted to work over scientific and theoretical problems of space flight. In the beginning of 1956 the Korolev's United Design Bureau was officially entrusted the creation and launch of undirected research satellite named "Object D" weighing 1.000-1.400 kg in 1957-1958. The main scientific management and development of scientific equipment was assigned to a commission of the Academy of Sciences of the USSR under the direction of . Keldysh. The measurement of parameters of the atmosphere, corpuscular radiation of the Sun, magnetic fields, space radiation etc. was planned during the "Object D" flight. The successful performance in the middle of 1956 of the second series of launches of geophysical rockets has allowed to gain a large volume of the information about parameters of physiological functions and behavior of animals in conditions of flight. For enlargement of these works the laboratory of V. Yazdovsky in the Institute of aviation medicine was extended to a department, the large group of the new employees, including V. Antipov, . Baevsky, I. Balakhovsky, B. Buylov, . Genin, O. Gazenko, A. Gurdjian, I. Kasyan, A. Kotovskaya, E..Yuganov, . Shepelev and others came to the department. But, owing to the delay of development of the scientific equipment for
Some Unknown Pages of the Living Organisms' First Orbital Flight
NASA Astrophysics Data System (ADS)
Malashenkov, D. C.
2002-01-01
The successful creation of ballistic rockets in USSR has allowed at the end of 1953 to make a real task of delivery of a payload into the Earth's orbit. In March 1954 during the meeting in the Academy of Sciences of USSR, the basic research problems conducted by means of artificial satellites of the Earth were determined. In May, 1954 S. Korolev has sent to Government of the USSR the report with the offer of creation the space satellites on the basis of intercontinental ballistic rocket -7 developed by him. It was the first time when the idea about possibility of interplanetary flights was stated in the official document. In August 1954 Council of Ministers of the USSR had ratified the submitted offers and have entrusted to work over scientific and theoretical problems of space flight. In the beginning of 1956 the Korolev's United Design Bureau was officially entrusted the creation and launch of undirected research satellite named "Object D" weighing 1.000-1.400 kg in 1957-1958. The main scientific management and development of scientific equipment was assigned to a commission of the Academy of Sciences of the USSR under the direction of . Keldysh. The measurement of parameters of the atmosphere, corpuscular radiation of the Sun, magnetic fields, space radiation etc. was planned during the "Object D" flight. The successful performance in the middle of 1956 of the second series of launches of geophysical rockets has allowed to gain a large volume of the information about parameters of physiological functions and behavior of animals in conditions of flight. For enlargement of these works the laboratory of V. Yazdovsky in the Institute of aviation medicine was extended to a department, the large group of the new employees, including V. Antipov, . Baevsky, I. Balakhovsky, B. Buylov, . Genin, O. Gazenko, A. Gurdjian, I. Kasyan, A. Kotovskaya, E..Yuganov, . Shepelev and others came to the department. But, owing to the delay of development of the scientific equipment for
INTRODUCTION: Surface Dynamics, Phonons, Adsorbate Vibrations and Diffusion
NASA Astrophysics Data System (ADS)
Bruch, L. W.
2004-07-01
components within the dilute nitrides. Electro-absorption and electro-refractive effects—Franz-Keldysh (FK) and quantum-confined Stark effect (QCSE) need to be studied theoretically in view of their importance for optical modulators. The aim of this special issue is to review the recent progress in theory, growth, characterization and device applications of dilute nitrides, and to collate what is known and what is not known in the field and address important fundamental physical properties and key material and device issues. The issue brings together a wide selection of papers from over 27 prominent research groups that have made key contributions to the field in the areas of research including growth, characterization and physical properties, devices and device integration, and theory and modelling. The editor is very grateful to all the invited authors for their contribution to this issue of Journal of Physics: Condensed Matter. I am grateful to Professors M J Adams, X Marie and Dr H Riechert for their help and contributions to the preparation of the editorial.
NASA Astrophysics Data System (ADS)
Fulling, S. A.
2006-05-01
classes of systems: quantum mechanics, linear (free) fields, and interacting fields. DeWitt's characteristic tools of effective actions, heat kernels, and ghost fields are developed. Chapters 26 and 31 outline new approaches developed in collaboration with DeWitt's recent students C Molina-Paris and C Y Wang, respectively. The first of these is a ghost-free formulation of gauge theory built on ideas of G A Vilkovisky. The second is a systematic attempt (following J Schwinger, L V Keldysh, and others) to replace the in-out matrix elements by expectation values in a single (initial) state. Most of parts VI and VII consist of special topics, such as anomalies, particle creation by external fields, Unruh acceleration temperature, black holes, and Euclideanization. Chapter 30, on black holes and Hawking radiation, will be very familiar to readers of DeWitt's influential review article [4]. Chapter 28, on anomalies, makes a careful distinction (missing from many treatments) between 'critical' anomalies, which render equations of motion inconsistent in the (would-be) quantum theory, and harmless anomalies that merely invalidate predictions that would classically follow from certain symmetries. The trace anomalies in the stress tensor of matter and the axial-current anomaly in quantum electrodynamics are harmless. Examples of critical anomalies are the chiral anomaly of a spinor field coupled to a non-Abelian gauge field and the anomaly in the conservation law of the stress tensor of certain pathological theories [5]. DeWitt's chapter calculates the trace and chiral anomalies in detail. The axial anomaly is mentioned only in a one-line summary (and not defined or indexed—generally speaking, I found the book's long index surprisingly unhelpful), and the Alvarez Witten anomaly is not mentioned at all. The last two chapters of part VII treat the most important particular quantum field theories. Chapter 34 develops many of the textbook predictions of quantum eletrodynamics from De
HISTORICAL MEMOIR: The play of light in crystals
NASA Astrophysics Data System (ADS)
Zakharchenya, Boris Petrovitch
2008-11-01
and experimentalists were taking part in the development of the concept of so-called polaritons in semiconductors, i.e. mixed states, when the 'mechanical' particle exciton mixes with the light wave. Pekar and Rashba of Kiev, Ginzburg and Agranovich of Moscow, Kaplyansky, Razbirin and Uraltsev of Leningrad, and also the above-mentioned American researchers, made the greatest contribution to the development of this sophisticated problem. Recalling the exciton physics of crystals of the 1950s and 1960s, I should call that time, after Schiller and Goethe, a period of Sturm und Drang. But even later on, the stormy waves of exciton spectroscopy did not calm down. There appeared lasers, which permitted Yaroslav Pokrovsky of the Institute of Electronics in Moscow to observe the hyperfine structure of exciton impurity complexes. The intense sources of light were also used for observation of the electron--hole condensate in semiconductors. But the initial idea of these investigations was stimulated by the existence of excitons: Bose particles and the attempt to observe their condensation. Veniamin Keldysh, Alexander Rogachev and a number of other Russian and foreign physicists contributed greatly to the solution of that problem. My friend, Carson Jeffries of Berkeley, a physicist and a painter, observed a gigantic (about a millimeter in size) electron--hole droplet in a crystal of germanium, and the results of his experiments were even mentioned in the New York Times. The 'exciton wave' rolled around the world, but its birthplace was Gross' small laboratory at the Physico-Technical Institute. It is most vexatious to read in a great many foreign textbooks on solid state physics that the Strasbourg professor S Nikitin was first to observe the exciton in cuprous oxide. That is not true at all! Nikitin bears no relation whatever to the discovery of the exciton. Gross first discovered a hydrogen-like series in a semiconductor in 1951 and published his findings in the Russian