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vaclav spicka

Fuzhou University, Semiconductors, senior scientist

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Saha Institute of Nuclear Physics

Prof Uchechukwu Vincent

Redeemer's University

Alexandre Martin

University of Kentucky

Samit Chakrabarty

University of Leeds

Mykhailo Moskalets

IFISC (UIB-CSIC)

Cyril Petitjean

Université de Liège

Chalmers University of Technology

Armando Marques-Guedes

UNL - New University of Lisbon

Gwen Robbins Schug

University of North Carolina at Greensboro

Gabriel Gutierrez-Alonso

University of Salamanca

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Papers by vaclav spicka

On physical processes controlling nerve signalling

The European Physical Journal Special Topics, Dec 18, 2023

Non-equilibrium quantum physics, many body systems, and foundations of quantum physics

The European Physical Journal Special Topics, Jan 8, 2024

Presented is a brief summary of recent developments of topics addressed by the reviews and origin... more Presented is a brief summary of recent developments of topics addressed by the reviews and original papers of this volume related to non-equilibrium phenomena in various (especially mesoscopic) systems, the foundations of quantum physics, quantum optics and related fields of physics including biophysics, cosmology, gravitation and astrophysics.

Tight-binding approach to resonant tunneling with electron-phonon coupling

Physical review, Dec 15, 1991

We consider resonant tunneling through a double barrier when the electrons interact with longitud... more We consider resonant tunneling through a double barrier when the electrons interact with longitudinal-optical phonons in the double-barrier well. We use a tight-binding model for the electron Hamiltonian, with a linear coupling to the phonon modes. Phonon-mediated scattering amplitudes for the double-barrier structure are efficiently obtained by a recursive Green-function technique. This technique allows us to go beyond the unrealistic assumption of Lorentzian line shapes, used in previous treatments. Our results are in qualitative agreement with earlier calculations, but quantitatively the phonon peaks are enhanced typically by 50%.

Quasiparticle Boltzmann equation in semiconductors

Physical review, Nov 15, 1995

The quasiparticle approximation and corrections beyond it are derived from expansion in the spiri... more The quasiparticle approximation and corrections beyond it are derived from expansion in the spirit of the virial corrections. This way, the Boltzmann equation for electrons in semiconductors is recovered from the nonequilibrium Green's functions without unjustified neglect of the former theory. The present approach gives higher-order contributions to the scattering rates and provides observables as functionals of the quasiparticle distribution. The application scheme is of the same simplicity as the one based on the quasiparticle approximation. Five applications to phenomena beyond the scope of the quasiparticle approximation are presented: two-phonon scattering rates, compensation. of wave-function renormalization for isotropic elastic scattering, quasiparticle back- Qow, backBow current of waves, and discussion of the collisional broadening.

Polarons by the coherent potential method

Czechoslovak Journal of Physics, Feb 1, 1984

Electron Systems Out of Equilibrium: Nonequilibrium Green's Function Approach

This review deals with the state of the art and perspectives of description of nonequilibrium man... more This review deals with the state of the art and perspectives of description of nonequilibrium many-body systems using the nonequilibrium Green's function (NGF) method. The basic aim is to describe time evolution of the many-body system from its initial state over its transient dynamics to its long time asymptotic evolution. First, we discuss basic aims of transport theories to motivate the introduction of the NGF techniques. Second, this article summarizes the present view on construction of the electron transport equations formulated within the NGF approach to nonequilibrium. We discuss incorporation of complex initial conditions to the NGF formalism, and the NGF reconstruction theorem, which serves as a tool to derive simplified kinetic equations. Three stages of evolution of the nonequilibrium, the first described by the full NGF description, the second by a non-Markovian generalized master equation and the third by a Markovian master equation will be related to each other.

Comparison of the collision delay and displacements within realistic potentials

We calculate the nonlocal shifts required in the extended Boltzmann (BUU) equation for different ... more We calculate the nonlocal shifts required in the extended Boltzmann (BUU) equation for different realistic potentials. The nonlocal shifts are interpreted in terms of the kinetic scattering events. Since the nonlocal shifts are given by off-shell derivatives of the scattering T-matrix we are able to compare the slight off-shell behavior of the different potentials by this way. While the Bonn one-Boson-exchange (A-C) and Paris potentials yield very close results, the separable Paris potential is found to provide different values from the others

On the Mathematical Structure of Physical Quantities

Hot topics in thermal analysis and calorimetry, 2017

Physics at the FMQT’08 conference

Physica E-low-dimensional Systems & Nanostructures, 2010

This paper summarizes the recent state of the art of the following topics presented at the FQMT'0... more This paper summarizes the recent state of the art of the following topics presented at the FQMT'04 conference: Quantum, mesoscopic and (partly) classical thermodynamics; Quantum limits to the second law of thermodynamics; Quantum measurement; Quantum decoherence and dephasing; Mesoscopic and nano-electro-mechanical systems; Classical molecular motors, ratchet systems and rectified motion; Quantum Brownian motion and Quantum motors; Physics of quantum computing; and Relevant experiments from the nanoscale to the macroscale. To all these subjects an introduction is given and the recent literature is broadly overviewed. The paper contains some 450 references in total.

Fast transients in mesoscopic systems

Nucleation and Atmospheric Aerosols, 2011

We study fast transient dynamics of an open quantum system at the initial stage of its equilibrat... more We study fast transient dynamics of an open quantum system at the initial stage of its equilibration starting far from equilibrium from correlated initial conditions reflecting entanglement with the environment. These correlations rapidly decay and the process enters the non-equilibrium quasi-particle mode controlled by a generalized master equation. As a model system, the nanoscopic molecular bridge between two leads is considered. The coupling to the leads is assumed to be intermittent. Properties of the resulting transients are demonstrated and analyzed.

AC conductance of quantum wires with inelastic scattering. I

Journal of Physics: Condensed Matter, Feb 12, 1990

The influence of inelastic processes on the coherence in the semiballistic regime of mesoscopic t... more The influence of inelastic processes on the coherence in the semiballistic regime of mesoscopic transport is investigated by calculating the AC conductance of electrons in a single-channel quantum wire, coupled to a bath of longitudinal acoustic phonons. Numerical results illustrate the situation in GaAs structures.

Physics at the FQMT’04 conference

Physica E-low-dimensional Systems & Nanostructures, Oct 1, 2005

This paper summarizes the recent state of the art of the following topics presented at the FQMT'0... more This paper summarizes the recent state of the art of the following topics presented at the FQMT'04 conference: Quantum, mesoscopic and (partly) classical thermodynamics; Quantum limits to the second law of thermodynamics; Quantum measurement; Quantum decoherence and dephasing; Mesoscopic and nano-electro-mechanical systems; Classical molecular motors, ratchet systems and rectified motion; Quantum Brownian motion and Quantum motors; Physics of quantum computing; and Relevant experiments from the nanoscale to the macroscale. To all these subjects an introduction is given and the recent literature is broadly overviewed. The paper contains some 450 references in total.

Correlated initial condition for an embedded process by time partitioning

Physical Review B, Jun 15, 2010

Study of transients in the electron quantum transport by nonequilibrium Green's function often re... more Study of transients in the electron quantum transport by nonequilibrium Green's function often requires an explicit inclusion of correlations at a finite initial time. For processes embedded in a host process, a universal treatment of the correlated initial conditions based on the formalism of partitioning in time allows to express their self-energy including the "irregular" correlation part in terms of the known properties of the host process. This unified formalism also yields the renormalized semigroup property for propagators and the reconstruction equations for the particle correlation function. The Bogolyubov principle of the decay of correlations then permits to buildup a theory of quantum transport equations with finite-time initial conditions.

Transient Magnetic Tunneling Mediated by a Molecular Bridge

Journal of Superconductivity and Novel Magnetism, Aug 26, 2014

This paper extends our recent theoretical study of transient currents in molecular bridge junctio... more This paper extends our recent theoretical study of transient currents in molecular bridge junctions [1] to magnetic tunneling. Presently, we calculate the excess magnetic tunneling through the molecular bridge shunting the junction. The system is represented by two ferromagnetic electrodes bridged by a molecular size island with one electronic level and a local Hubbard type correlation. The island is linked with the electrodes by tunneling junctions whose coupling strength is assumed to undergo rapid changes affecting the connectivity of the system. We employ the non-equilibrium Green's functions. The numerical solution is obtained solving the real-time Dyson equation in the integro-differential form self-consistently. The switching events controlling the junctions give rise to transient changes of magnetisation of the island. They strongly depend on the static galvanic bias between the electrodes, mutual alignment of their magnetisation and on the time scale of the switching.

Fast dynamics of molecular bridges

Physica Scripta, Nov 1, 2012

We address the dynamics of open quantum systems, when complex finite time initial conditions, an ... more We address the dynamics of open quantum systems, when complex finite time initial conditions, an ensuing rapid nonequilibrium transient, quantum interferences and their attenuation play important roles. To study all these phenomena in conditions of general non-equilibrium, open systems are represented by a simple structure of a molecular island between two leads. We treat this model using the Nonequilibrium Greens Functions (NGF) method for a finite initial condition. We demonstrate that the non-interacting molecular bridge model captures well many features of general open quantum systems. Three stages of its nonequilibrium evolution, the first described by the full NGF description, the second, ruled by the asymptotically exact Generalized master equation (GME) and the third, governed by a Markovian master equation (ME), are delineated and related to each other.

Dynamics of mesoscopic systems: Non-equilibrium Green's functions approach

Physica E-low-dimensional Systems & Nanostructures, 2010

Recent developments in technologies and experiments enable us to observe dynamical behavior of ve... more Recent developments in technologies and experiments enable us to observe dynamical behavior of very small quantum systems under conditions when it is sensitive to system parameters, internal interactions, the environment and the external time-dependent fields. This contribution deals with the status and perspectives of description of such truly non-equilibrium quantum many body systems using the non-equilibrium Green's functions (NGF). The basic aim of this approach is to describe time development of the many-body system out of equilibrium from its initial state over its transient dynamics to its long time asymptotic evolution. The early stages of the transient evolution will be characterized for a broad class of the initial conditions generated in the course of Keldysh switch-on states. Gradual loss of initial correlations due to interactions and related renormalization processes in the system may, under favorable conditions, give rise to the evolution stage expressible in terms of non-equilibrium quasiparticles. This permits to reduce the description of the system behavior to a quantum transport equation. The consistency of such approximations for NGF may be judged by checking the non-equilibrium version of transport Ward identities. These identities follow from the gauge invariance of the 1st kind for NGF. To cover the whole time domain of the transient, we obtain the non-equilibrium Ward identities for NGF with initial conditions included.

Fast Transient Current Response to Switching Events in Short Chains of Molecular Islands

Journal of Superconductivity and Novel Magnetism, Dec 29, 2012

We consider current flow between two metallic leads joined by a short chain of molecular islands ... more We consider current flow between two metallic leads joined by a short chain of molecular islands interconnected by tunneling junctions. These junctions are assumed to be "wiggly", that is switching on and off intermittently. The resulting current response is composed of fast transients which may or may not overlap depending on the ratio between the interplay of the switching times and the dynamical characteristics of the chain, notably the formation time of the quasiparticles and the decay time of "initial" correlations induced by each switching event. The process is described in terms of non-equilibrium Green's functions using a combination of partition techniques in space and in time to solve the integrodifferential equations for the particle correlation function numerically. Several model for the switching are explored, among them the case of bursts of swichings within a limited time followed by a quiescent period. For this, we concentrate on the gradual transition to the steady transport regime.

Long and short time quantum dynamics: III. Transients

Physica E-low-dimensional Systems & Nanostructures, Oct 1, 2005

The quantum transport equations for fast transients have the structure of a Generalized Master Eq... more The quantum transport equations for fast transients have the structure of a Generalized Master Equations for the single-particle distribution, with causal memory terms. Nonequilibrium Green's functions are reduced to GME if the Generalized Kadanoff-Baym Ansatz is applied. This Ansatz has been used with success both to non-linear transport and to optical transients in semiconductors ; further progress is linked with its extension to a family of the Causal Ansatzes, differing primarily in renormalization of the propagators. For the switch-on non-equilibrium states, generated by a perturbation from equilibrium, the renormalization to the dark dressed Green's function followed by calculation of the induced self-energies is a productive direction. It also circumvents the problem of correlated initial conditions, far from a general solution otherwise. Such initial conditions appear as incompatible with a Causal Ansatz in general. The presently available formalism permits to study a transient process in the whole time range using the complete NGF, but making a flexible Ansatz-based reduction appropriate to the stage of dynamic evolution.

Coherent electronic transport properties of quasi-one-dimensional systems

Surface Science, Apr 1, 1990

... C 21 (1988), p. L1147. [11]J. Masek and B. Kramer, Solid State Commun. ... Full Text via Cros... more

Quasiparticle states of electron systems out of equilibrium

Physical Review B, May 22, 2007

In a nonequilibrium system, quasiparticles are defined, consistently with the construction of qua... more In a nonequilibrium system, quasiparticles are defined, consistently with the construction of quantum transport equations, as one-electron excitations whose propagator possesses a time-local optical potential. This potential is constructed as a solution of the phase equation, a self-consistency condition reducing the renormalized Dyson equation to a formerly proposed multiplicative composition rule for the propagators. The Dyson equation for the particle correlation function is transformed to a renormalized quasiparticle reconstruction equation, whose leading term represents the quasiparticle Kadanoff-Baym ansatz ͓Physica E 29, 196 ͑2005͔͒, an improvement over the standard generalized Kadanoff-Baym ansatz.

On physical processes controlling nerve signalling

The European Physical Journal Special Topics, Dec 18, 2023

Non-equilibrium quantum physics, many body systems, and foundations of quantum physics

The European Physical Journal Special Topics, Jan 8, 2024

Presented is a brief summary of recent developments of topics addressed by the reviews and origin... more Presented is a brief summary of recent developments of topics addressed by the reviews and original papers of this volume related to non-equilibrium phenomena in various (especially mesoscopic) systems, the foundations of quantum physics, quantum optics and related fields of physics including biophysics, cosmology, gravitation and astrophysics.

Tight-binding approach to resonant tunneling with electron-phonon coupling

Physical review, Dec 15, 1991

We consider resonant tunneling through a double barrier when the electrons interact with longitud... more We consider resonant tunneling through a double barrier when the electrons interact with longitudinal-optical phonons in the double-barrier well. We use a tight-binding model for the electron Hamiltonian, with a linear coupling to the phonon modes. Phonon-mediated scattering amplitudes for the double-barrier structure are efficiently obtained by a recursive Green-function technique. This technique allows us to go beyond the unrealistic assumption of Lorentzian line shapes, used in previous treatments. Our results are in qualitative agreement with earlier calculations, but quantitatively the phonon peaks are enhanced typically by 50%.

Quasiparticle Boltzmann equation in semiconductors

Physical review, Nov 15, 1995

The quasiparticle approximation and corrections beyond it are derived from expansion in the spiri... more The quasiparticle approximation and corrections beyond it are derived from expansion in the spirit of the virial corrections. This way, the Boltzmann equation for electrons in semiconductors is recovered from the nonequilibrium Green's functions without unjustified neglect of the former theory. The present approach gives higher-order contributions to the scattering rates and provides observables as functionals of the quasiparticle distribution. The application scheme is of the same simplicity as the one based on the quasiparticle approximation. Five applications to phenomena beyond the scope of the quasiparticle approximation are presented: two-phonon scattering rates, compensation. of wave-function renormalization for isotropic elastic scattering, quasiparticle back- Qow, backBow current of waves, and discussion of the collisional broadening.

Polarons by the coherent potential method

Czechoslovak Journal of Physics, Feb 1, 1984

Electron Systems Out of Equilibrium: Nonequilibrium Green's Function Approach

This review deals with the state of the art and perspectives of description of nonequilibrium man... more This review deals with the state of the art and perspectives of description of nonequilibrium many-body systems using the nonequilibrium Green's function (NGF) method. The basic aim is to describe time evolution of the many-body system from its initial state over its transient dynamics to its long time asymptotic evolution. First, we discuss basic aims of transport theories to motivate the introduction of the NGF techniques. Second, this article summarizes the present view on construction of the electron transport equations formulated within the NGF approach to nonequilibrium. We discuss incorporation of complex initial conditions to the NGF formalism, and the NGF reconstruction theorem, which serves as a tool to derive simplified kinetic equations. Three stages of evolution of the nonequilibrium, the first described by the full NGF description, the second by a non-Markovian generalized master equation and the third by a Markovian master equation will be related to each other.

Comparison of the collision delay and displacements within realistic potentials

We calculate the nonlocal shifts required in the extended Boltzmann (BUU) equation for different ... more We calculate the nonlocal shifts required in the extended Boltzmann (BUU) equation for different realistic potentials. The nonlocal shifts are interpreted in terms of the kinetic scattering events. Since the nonlocal shifts are given by off-shell derivatives of the scattering T-matrix we are able to compare the slight off-shell behavior of the different potentials by this way. While the Bonn one-Boson-exchange (A-C) and Paris potentials yield very close results, the separable Paris potential is found to provide different values from the others

On the Mathematical Structure of Physical Quantities

Hot topics in thermal analysis and calorimetry, 2017

Physics at the FMQT’08 conference

Physica E-low-dimensional Systems & Nanostructures, 2010

This paper summarizes the recent state of the art of the following topics presented at the FQMT'0... more This paper summarizes the recent state of the art of the following topics presented at the FQMT'04 conference: Quantum, mesoscopic and (partly) classical thermodynamics; Quantum limits to the second law of thermodynamics; Quantum measurement; Quantum decoherence and dephasing; Mesoscopic and nano-electro-mechanical systems; Classical molecular motors, ratchet systems and rectified motion; Quantum Brownian motion and Quantum motors; Physics of quantum computing; and Relevant experiments from the nanoscale to the macroscale. To all these subjects an introduction is given and the recent literature is broadly overviewed. The paper contains some 450 references in total.

Fast transients in mesoscopic systems

Nucleation and Atmospheric Aerosols, 2011

We study fast transient dynamics of an open quantum system at the initial stage of its equilibrat... more We study fast transient dynamics of an open quantum system at the initial stage of its equilibration starting far from equilibrium from correlated initial conditions reflecting entanglement with the environment. These correlations rapidly decay and the process enters the non-equilibrium quasi-particle mode controlled by a generalized master equation. As a model system, the nanoscopic molecular bridge between two leads is considered. The coupling to the leads is assumed to be intermittent. Properties of the resulting transients are demonstrated and analyzed.

AC conductance of quantum wires with inelastic scattering. I

Journal of Physics: Condensed Matter, Feb 12, 1990

The influence of inelastic processes on the coherence in the semiballistic regime of mesoscopic t... more The influence of inelastic processes on the coherence in the semiballistic regime of mesoscopic transport is investigated by calculating the AC conductance of electrons in a single-channel quantum wire, coupled to a bath of longitudinal acoustic phonons. Numerical results illustrate the situation in GaAs structures.

Physics at the FQMT’04 conference

Physica E-low-dimensional Systems & Nanostructures, Oct 1, 2005

This paper summarizes the recent state of the art of the following topics presented at the FQMT'0... more This paper summarizes the recent state of the art of the following topics presented at the FQMT'04 conference: Quantum, mesoscopic and (partly) classical thermodynamics; Quantum limits to the second law of thermodynamics; Quantum measurement; Quantum decoherence and dephasing; Mesoscopic and nano-electro-mechanical systems; Classical molecular motors, ratchet systems and rectified motion; Quantum Brownian motion and Quantum motors; Physics of quantum computing; and Relevant experiments from the nanoscale to the macroscale. To all these subjects an introduction is given and the recent literature is broadly overviewed. The paper contains some 450 references in total.

Correlated initial condition for an embedded process by time partitioning

Physical Review B, Jun 15, 2010

Study of transients in the electron quantum transport by nonequilibrium Green's function often re... more Study of transients in the electron quantum transport by nonequilibrium Green's function often requires an explicit inclusion of correlations at a finite initial time. For processes embedded in a host process, a universal treatment of the correlated initial conditions based on the formalism of partitioning in time allows to express their self-energy including the "irregular" correlation part in terms of the known properties of the host process. This unified formalism also yields the renormalized semigroup property for propagators and the reconstruction equations for the particle correlation function. The Bogolyubov principle of the decay of correlations then permits to buildup a theory of quantum transport equations with finite-time initial conditions.

Transient Magnetic Tunneling Mediated by a Molecular Bridge

Journal of Superconductivity and Novel Magnetism, Aug 26, 2014

This paper extends our recent theoretical study of transient currents in molecular bridge junctio... more This paper extends our recent theoretical study of transient currents in molecular bridge junctions [1] to magnetic tunneling. Presently, we calculate the excess magnetic tunneling through the molecular bridge shunting the junction. The system is represented by two ferromagnetic electrodes bridged by a molecular size island with one electronic level and a local Hubbard type correlation. The island is linked with the electrodes by tunneling junctions whose coupling strength is assumed to undergo rapid changes affecting the connectivity of the system. We employ the non-equilibrium Green's functions. The numerical solution is obtained solving the real-time Dyson equation in the integro-differential form self-consistently. The switching events controlling the junctions give rise to transient changes of magnetisation of the island. They strongly depend on the static galvanic bias between the electrodes, mutual alignment of their magnetisation and on the time scale of the switching.

Fast dynamics of molecular bridges

Physica Scripta, Nov 1, 2012

We address the dynamics of open quantum systems, when complex finite time initial conditions, an ... more We address the dynamics of open quantum systems, when complex finite time initial conditions, an ensuing rapid nonequilibrium transient, quantum interferences and their attenuation play important roles. To study all these phenomena in conditions of general non-equilibrium, open systems are represented by a simple structure of a molecular island between two leads. We treat this model using the Nonequilibrium Greens Functions (NGF) method for a finite initial condition. We demonstrate that the non-interacting molecular bridge model captures well many features of general open quantum systems. Three stages of its nonequilibrium evolution, the first described by the full NGF description, the second, ruled by the asymptotically exact Generalized master equation (GME) and the third, governed by a Markovian master equation (ME), are delineated and related to each other.

Dynamics of mesoscopic systems: Non-equilibrium Green's functions approach

Physica E-low-dimensional Systems & Nanostructures, 2010

Recent developments in technologies and experiments enable us to observe dynamical behavior of ve... more Recent developments in technologies and experiments enable us to observe dynamical behavior of very small quantum systems under conditions when it is sensitive to system parameters, internal interactions, the environment and the external time-dependent fields. This contribution deals with the status and perspectives of description of such truly non-equilibrium quantum many body systems using the non-equilibrium Green's functions (NGF). The basic aim of this approach is to describe time development of the many-body system out of equilibrium from its initial state over its transient dynamics to its long time asymptotic evolution. The early stages of the transient evolution will be characterized for a broad class of the initial conditions generated in the course of Keldysh switch-on states. Gradual loss of initial correlations due to interactions and related renormalization processes in the system may, under favorable conditions, give rise to the evolution stage expressible in terms of non-equilibrium quasiparticles. This permits to reduce the description of the system behavior to a quantum transport equation. The consistency of such approximations for NGF may be judged by checking the non-equilibrium version of transport Ward identities. These identities follow from the gauge invariance of the 1st kind for NGF. To cover the whole time domain of the transient, we obtain the non-equilibrium Ward identities for NGF with initial conditions included.

Fast Transient Current Response to Switching Events in Short Chains of Molecular Islands

Journal of Superconductivity and Novel Magnetism, Dec 29, 2012

We consider current flow between two metallic leads joined by a short chain of molecular islands ... more We consider current flow between two metallic leads joined by a short chain of molecular islands interconnected by tunneling junctions. These junctions are assumed to be "wiggly", that is switching on and off intermittently. The resulting current response is composed of fast transients which may or may not overlap depending on the ratio between the interplay of the switching times and the dynamical characteristics of the chain, notably the formation time of the quasiparticles and the decay time of "initial" correlations induced by each switching event. The process is described in terms of non-equilibrium Green's functions using a combination of partition techniques in space and in time to solve the integrodifferential equations for the particle correlation function numerically. Several model for the switching are explored, among them the case of bursts of swichings within a limited time followed by a quiescent period. For this, we concentrate on the gradual transition to the steady transport regime.

Long and short time quantum dynamics: III. Transients

Physica E-low-dimensional Systems & Nanostructures, Oct 1, 2005

The quantum transport equations for fast transients have the structure of a Generalized Master Eq... more The quantum transport equations for fast transients have the structure of a Generalized Master Equations for the single-particle distribution, with causal memory terms. Nonequilibrium Green's functions are reduced to GME if the Generalized Kadanoff-Baym Ansatz is applied. This Ansatz has been used with success both to non-linear transport and to optical transients in semiconductors ; further progress is linked with its extension to a family of the Causal Ansatzes, differing primarily in renormalization of the propagators. For the switch-on non-equilibrium states, generated by a perturbation from equilibrium, the renormalization to the dark dressed Green's function followed by calculation of the induced self-energies is a productive direction. It also circumvents the problem of correlated initial conditions, far from a general solution otherwise. Such initial conditions appear as incompatible with a Causal Ansatz in general. The presently available formalism permits to study a transient process in the whole time range using the complete NGF, but making a flexible Ansatz-based reduction appropriate to the stage of dynamic evolution.

Coherent electronic transport properties of quasi-one-dimensional systems

Surface Science, Apr 1, 1990

... C 21 (1988), p. L1147. [11]J. Masek and B. Kramer, Solid State Commun. ... Full Text via Cros... more

Quasiparticle states of electron systems out of equilibrium

Physical Review B, May 22, 2007

In a nonequilibrium system, quasiparticles are defined, consistently with the construction of qua... more In a nonequilibrium system, quasiparticles are defined, consistently with the construction of quantum transport equations, as one-electron excitations whose propagator possesses a time-local optical potential. This potential is constructed as a solution of the phase equation, a self-consistency condition reducing the renormalized Dyson equation to a formerly proposed multiplicative composition rule for the propagators. The Dyson equation for the particle correlation function is transformed to a renormalized quasiparticle reconstruction equation, whose leading term represents the quasiparticle Kadanoff-Baym ansatz ͓Physica E 29, 196 ͑2005͔͒, an improvement over the standard generalized Kadanoff-Baym ansatz.