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Jun 28, 2018
06/18

by
E. Perfetto; D. Sangalli; A. Marini; G. Stefanucci

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In this work we propose an accurate first-principle approach to calculate the transient photo--absorption spectrum measured in Pump\&\,Probe experiments. We formulate a condition of {\em adiabaticity} and thoroughly analyze the simplifications brought about by the fulfillment of this condition in the non--equilibrium Green's function (NEGF) framework. Starting from the Kadanoff-Baym equations we derive a non--equilibrium Bethe--Salpeter equation (BSE) for the response function that can be...

Topics: Condensed Matter, Other Condensed Matter

Source: http://arxiv.org/abs/1507.01786

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Sep 23, 2013
09/13

by
P. Myöhänen; R. Tuovinen; T. Korhonen; G. Stefanucci; R. van Leeuwen

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In this work we investigate the effects of the electron-electron interaction between a molecular junction and the metallic leads in time-dependent quantum transport. We employ the recently developed embedded Kadanoff-Baym method [Phys. Rev. B 80, 115107 (2009)] and show that the molecule-lead interaction changes substantially the transient and steady-state transport properties. We first show that the mean-field Hartree-Fock (HF) approximation does not capture the polarization effects...

Source: http://arxiv.org/abs/1111.6104v1

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Jun 30, 2018
06/18

by
G. Stefanucci; Y. Pavlyukh; A. -M. Uimonen; R. van Leeuwen

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We present a diagrammatic approach to construct self-energy approximations within many-body perturbation theory with positive spectral properties. The method cures the problem of negative spectral functions which arises from a straightforward inclusion of vertex diagrams beyond the GW approximation. Our approach consists of a two-steps procedure: we first express the approximate many-body self-energy as a product of half-diagrams and then identify the minimal number of half-diagrams to add in...

Topics: Other Condensed Matter, Condensed Matter

Source: http://arxiv.org/abs/1408.6163

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Jun 28, 2018
06/18

by
E. Perfetto; A. -M. Uimonen; R. van Leeuwen; G. Stefanucci

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We put forward a first-principle NonEquilibrium Green's Function (NEGF) approach to calculate the transient photoabsorption spectrum of optically thin samples. The method can deal with pump fields of arbitrary strength, frequency and duration as well as for overlapping and nonoverlapping pump and probe pulses. The electron-electron repulsion is accounted for by the correlation self-energy, and the resulting numerical scheme deals with matrices that scale quadratically with the system size. Two...

Topics: Mesoscale and Nanoscale Physics, Atomic Physics, Physics, Condensed Matter

Source: http://arxiv.org/abs/1507.05590

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Sep 18, 2013
09/13

by
S. Kurth; G. Stefanucci; C. -O. Almbladh; A. Rubio; E. K. U. Gross

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We present a computationally tractable scheme of time-dependent transport phenomena within open-boundary time-dependent density-functional-theory. Within this approach all the response properties of a system are determined from the time-propagation of the set of ``occupied'' Kohn-Sham orbitals under the influence of the external bias. This central idea is combined with an open-boundary description of the geometry of the system that is divided into three regions: left/right leads and the device...

Source: http://arxiv.org/abs/cond-mat/0502391v1

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Jun 29, 2018
06/18

by
S. Kurth; G. Stefanucci

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The single-impurity Anderson model is studied within the i-DFT framework, a recently proposed extension of density functional theory (DFT) for the description of electron transport in the steady state. i-DFT is designed to give both the steady current and density at the impurity, and it requires the knowledge of the exchange-correlation (xc) bias and on-site potential (gate). In this work we construct an approximation for both quantities which is accurate in a wide range of temperatures, gates...

Topics: Condensed Matter, Strongly Correlated Electrons

Source: http://arxiv.org/abs/1605.09330

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Jun 29, 2018
06/18

by
Y. Pavlyukh; A. -M. Uimonen; G. Stefanucci; R. van Leeuwen

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We present a systematic study of vertex corrections in the homogeneous electron gas at metallic densities. The vertex diagrams are built using a recently proposed positive-definite diagrammatic expansion for the spectral function. The vertex function not only provides corrections to the well known plasmon and particle-hole scatterings, but also gives rise to new physical processes such as generation of two plasmon excitations or the decay of the one-particle state into a two-particles-one-hole...

Topics: Condensed Matter, Strongly Correlated Electrons

Source: http://arxiv.org/abs/1607.04309

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3.0

Jun 30, 2018
06/18

by
E. Perfetto; G. Stefanucci; H. Kamata; T. Fujisawa

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The recent observation of charge fractionalization in single Tomanga-Luttinger liquids (TLLs) [Kamata et al., Nature Nanotech., 9 177 (2014)] opens new routes for a systematic investigation of this exotic quantum phenomenon. In this Letter we perform measurements on two adjacent TLLs and put forward an accurate theoretical framework to address the experiments. The theory is based on the plasmon scattering approach and can deal with injected charge pulses of arbitrary shape in TLL regions. We...

Topics: Mesoscale and Nanoscale Physics, Condensed Matter

Source: http://arxiv.org/abs/1405.2660

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Sep 22, 2013
09/13

by
S. Kurth; G. Stefanucci

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For molecules weakly coupled to leads the exact linear Kohn-Sham (KS) conductance can be orders of magnitude larger than the true linear conductance due to the lack of dynamical exchange-correlation (xc) corrections. In this work we show how to incorporate dynamical effects in KS transport calculations. The only quantity needed is the static xc potential in the molecular junction. Our scheme provides a comprehensive description of Coulomb blockade without breaking the spin symmetry. This is...

Source: http://arxiv.org/abs/1302.4362v2

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Sep 21, 2013
09/13

by
G. Stefanucci; S. Kurth

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We demonstrate that the zero-temperature conductance of the Anderson model can be calculated within the Landauer formalism combined with static density functional theory (DFT). The proposed approximate functional is based on finite-temperature DFT and yields the exact Kohn-Sham potential at the particle-hole symmetric point. Furthermore, in the limit of zero temperature it correctly exhibits a derivative discontinuity which is shown to be essential to reproduce the conductance plateau. On the...

Source: http://arxiv.org/abs/1106.3728v2

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Sep 20, 2013
09/13

by
E. Khosravi; S. Kurth; G. Stefanucci; E. K. U. Gross

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Charge transport through a nanoscale junction coupled to two macroscopic electrodes is investigated for the situation when bound states are present. We provide numerical evidence that bound states give rise to persistent, non-decaying current oscillations in the junction. We also show that the amplitude of these oscillations can exhibit a strong dependence on the history of the applied potential as well as on the initial equilibrium configuration. Our simulations allow for a quantitative...

Source: http://arxiv.org/abs/0802.2516v1

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Sep 19, 2013
09/13

by
G. Stefanucci; S. Kurth; A. Rubio; E. K. U. Gross

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We propose a time-dependent approach to investigate the motion of electrons in quantum pump device configurations. The occupied one-particle states are propagated in real time and used to calculate the local electron density and current. An advantage of the present computational scheme is that the same computational effort is required to simulate monochromatic, polychromatic and nonperiodic drivings. Furthermore, initial state dependence and history effects are naturally accounted for. This...

Source: http://arxiv.org/abs/cond-mat/0701279v1

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Sep 18, 2013
09/13

by
R. van Leeuwen; G. Stefanucci

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We present a compact and simplified proof of a generalized Wick theorem to calculate the Green's function of bosonic and fermionic systems in an arbitrary initial state. It is shown that the decomposition of the non-interacting $n$-particle Green's function is equivalent to solving a boundary problem for the Martin-Schwinger hierarchy; for non-correlated initial states a one-line proof of the standard Wick theorem is given. Our result leads to new self-energy diagrams and an elegant relation...

Source: http://arxiv.org/abs/1102.4814v2

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Jul 20, 2013
07/13

by
A. -M. Uimonen; E. Khosravi; A. Stan; G. Stefanucci; S. Kurth; R. van Leeuwen; E. K. U. Gross

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We study time-dependent electron transport through an Anderson model. The electronic interactions on the impurity site are included via the self-energy approximations at Hartree-Fock (HF), second Born (2B), GW, and T-Matrix level as well as within a time-dependent density functional (TDDFT) scheme based on the adiabatic Bethe-Ansatz local density approximation (ABALDA) for the exchange correlation potential. The Anderson model is driven out of equilibrium by applying a bias to the leads and its...

Source: http://arxiv.org/abs/1107.0162v2

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5.0

Jun 29, 2018
06/18

by
E. Perfetto; D. Sangalli; A. Marini; G. Stefanucci

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We show that any {\em quasi-particle} or GW approximation to the self-energy does not capture excitonic features in time-resolved (TR) photoemission spectroscopy. In this work we put forward a first-principles approach and propose a feasible diagrammatic approximation to solve this problem. We also derive an alternative formula for the TR photocurrent which involves a single time-integral of the lesser Green's function. The diagrammatic approximation applies to the {\em relaxed} regime...

Topics: Mesoscale and Nanoscale Physics, Condensed Matter, Other Condensed Matter

Source: http://arxiv.org/abs/1607.06449

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Jul 19, 2013
07/13

by
E. Perfetto; G. Stefanucci; M. Cini

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We demonstrate the remnant presence of {\em initial} correlations in the {\em steady-state} electrical current flowing between low-dimensional interacting leads. The leads are described as Luttinger liquids and electrons can tunnel via a quantum point-contact. We derive an analytic result for the time-dependent current and show that ground-state correlations have a large impact on the relaxation and long-time behavior. In particular, the I-V characteristic cannot be reproduced by quenching the...

Source: http://arxiv.org/abs/1005.3127v2

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Sep 23, 2013
09/13

by
S. Kurth; G. Stefanucci

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The cornerstone of time-dependent (TD) density functional theory (DFT), the Runge-Gross theorem, proves a one-to-one correspondence between TD potentials and TD densities of continuum Hamiltonians. In all practical implementations, however, the basis set is discrete and the system is effectively described by a lattice Hamiltonian. We point out the difficulties of generalizing the Runge-Groos proof to the discrete case and thereby endorse the recently proposed TD bond-current functional theory...

Source: http://arxiv.org/abs/1012.4296v2

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Jun 27, 2018
06/18

by
E. Perfetto; G. Stefanucci

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The physical interpretation of time-resolved photoabsorption experiments is not as straightforward as for the more conventional photoabsorption experiments conducted on equilibrium systems. In fact, the relation between the transient photoabsorption spectrum and the properties of the examined sample can be rather intricate since the former is a complicated functional of both the driving pump and the feeble probe fields. In this work we critically review the derivation of the time-resolved...

Topics: Other Condensed Matter, Condensed Matter, Physics, Atomic Physics

Source: http://arxiv.org/abs/1504.01902

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12

Jun 27, 2018
06/18

by
A. -M. Uimonen; G. Stefanucci; Y. Pavlyukh; R. van Leeuwen

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In a recent paper [Phys. Rev. B 90, 115134 (2014)] we put forward a diagrammatic expansion for the self-energy which guarantees the positivity of the spectral function. In this work we extend the theory to the density response function. We write the generic diagram for the density-response spectrum as the sum of partitions. In a partition the original diagram is evaluated using time-ordered Green's functions (GF) on the left-half of the diagram, antitime-ordered GF on the right-half of the...

Topics: Other Condensed Matter, Condensed Matter, Strongly Correlated Electrons

Source: http://arxiv.org/abs/1503.02158

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Jun 27, 2018
06/18

by
G. Stefanucci; S. Kurth

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In the framework of density functional theory a formalism to describe electronic transport in the steady state is proposed which uses the density on the junction and the {\em steady current} as basic variables. We prove that, in a finite window around zero bias, there is a one-to-one map between the basic variables and both local potential on as well as bias across the junction. The resulting Kohn-Sham system features two exchange-correlation (xc) potentials, a local xc potential and an xc...

Topics: Mesoscale and Nanoscale Physics, Condensed Matter

Source: http://arxiv.org/abs/1505.07364

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Jun 27, 2018
06/18

by
E. Perfetto; G. Stefanucci

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We study the combined effects of electron-phonon coupling and dot-lead repulsion in the transport properties of the Anderson-Holstein model. We employ a recently proposed nonperturbative method to calculate the transient response of the system. By varying the initial conditions for the time propagation the current exhibits transient oscillations of different nature. We are able to disentangle two dynamical processes, namely the local charge rearrangement due to the dot-lead contacting and the...

Topics: Condensed Matter, Mesoscale and Nanoscale Physics

Source: http://arxiv.org/abs/1503.03288

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Sep 18, 2013
09/13

by
E. Perfetto; G. Stefanucci

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We present a comprehensive analysis of the relaxation dynamics of a Luttinger liquid subject to a sequence of sudden interaction quenches. We express the critical exponent $\beta$ governing the decay of the steady-state propagator as an explicit functional of the switching protocol. At long distances $\beta$ depends only on the initial state while at short distances it is also history dependent. Continuous protocols of arbitrary complexity can be realized with infinitely long sequences. For...

Source: http://arxiv.org/abs/1102.4994v1

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Sep 21, 2013
09/13

by
A. -M. Uimonen; E. Khosravi; G. Stefanucci; S. Kurth; R. van Leeuwen; E. K. U. Gross

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We study transport through an interacting model system consisting of a central correlated site coupled to finite bandwidth tight-binding leads, which are considered as effectively noninteracting. Its nonequilibrium properties are determined by real-time propagation of the Kadanoff-Baym equations after applying a bias voltage to the system. The electronic interactions on the central site are incorporated by means of self-energy approximations at Hartree-Fock, second Born and GW level. We...

Source: http://arxiv.org/abs/1106.5631v1

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Sep 24, 2013
09/13

by
E. Khosravi; A. -M. Uimonen; A. Stan; G. Stefanucci; S. Kurth; R. van Leeuwen; E. K. U. Gross

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The possibility of finding multistability in the density and current of an interacting nanoscale junction coupled to semi-infinite leads is studied at various levels of approximation. The system is driven out of equilibrium by an external bias and the non-equilibrium properties are determined by real-time propagation using both time-dependent density functional theory (TDDFT) and many-body perturbation theory (MBPT). In TDDFT the exchange-correlation effects are described within a recently...

Source: http://arxiv.org/abs/1112.2871v1

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Sep 18, 2013
09/13

by
E. Khosravi; G. Stefanucci; S. Kurth; E. K. U. Gross

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The presence of bound states in a nanoscale electronic system attached to two biased, macroscopic electrodes is shown to give rise to persistent, non-decaying, localized current oscillations which can be much larger than the steady part of the current. The amplitude of these oscillations depends on the entire history of the applied potential. The bound-state contribution to the {\em static} density is history-dependent as well. Moreover, the time-dependent formulation leads to a natural...

Source: http://arxiv.org/abs/0803.0914v1

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Sep 23, 2013
09/13

by
E. Perfetto; G. Stefanucci; M. Cini

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The effects of long-range interactions in quantum transport are still largely unexplored, mainly due to the difficulty of devising efficient embedding schemes. In this work we present a substantial progress in the interacting resonant level model by reducing the problem to the solution of Kadanoff-Baym-like equations with a correlated embedding self-energy. The method allows us to deal with short- and long-range interactions and is applicable from the transient to the steady-state regime....

Source: http://arxiv.org/abs/1110.5161v1