Ultrafast dynamics of finite Hubbard clusters: A stochastic mean-field approach

Lacroix, Denis; Hermanns, S.; Hinz, Christopher; Bönitz, M.

doi:10.1103/physrevb.90.125112

Cited by 43 publications

(60 citation statements)

References 33 publications

(37 reference statements)

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“…In nuclear physics this approach, called stochastic mean field [36], has been originally introduced such that initial fluctuations in collective space are reproduced through arXiv:1609.01424v2 [nucl-th] 21 Mar 2017 fluctuations of the initial one-body density. In a series of works, it was shown that it surprisingly well accounts for correlations beyond mean-field [37][38][39] while treating properly the dynamic close to a spontaneous symmetry breaking [38]. It is also able to include approximately many-body correlation to all orders by connecting the evolution to the BBGKY hierarchy [40].…”

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confidence: 99%

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Microscopic Phase-Space Exploration Modeling ofFm258Spontaneous Fission

2017

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We show that the total kinetic energy (TKE) of nuclei after the spontaneous fission of 258 Fm can be well reproduced using simple assumptions on the quantum collective phase-space explored by the nucleus after passing the fission barrier. Assuming energy conservation and phase-space exploration according to the stochastic mean-field approach, a set of initial densities is generated. Each density is then evolved in time using the nuclear time-dependent density-functional theory with pairing. This approach goes beyond mean-field by allowing spontaneous symmetry breaking as well as a wider dynamical phase-space exploration leading to larger fluctuations in collective space. The total kinetic energy and mass distributions are calculated. New information on the fission process: fluctuations in scission time, strong correlation between TKE and collective deformation as well as pre-scission particle emission, are obtained. We conclude that fluctuations of TKE and mass are triggered by quantum fluctuations.PACS numbers: 21.60. Jz, 24.75.+i, 25.85.Ca, 27.90.+b The dynamical modeling of a nuclear Fermi quantum droplet that spontaneously breaks into two pieces represents one of the most exciting challenges of nuclear physics today. Beside its description, a deeper microscopic understanding of spontaneous fission (SF) is of great importance to form the heaviest elements at the frontier of the nuclear chart [1][2][3] or to further improve our knowledge about the competition between the r-process and fission during the primordial nucleosynthesis [4]. Motivated also by its importance in nuclear energy production, intensive experimental efforts have been made to accumulate precise measurements [5][6][7][8][9]. In recent years, an increasing effort was made to remove empirical ingredients that are employed in macroscopic modeling of fission and use microscopic theories [10,11]. The nuclear Density Functional Theory (DFT) is a suitable starting point to describe some aspects related to the large amplitude collective motion (LACM). A minimal information obtained from DFT is the adiabatic collective energy landscape [11]. One challenge to describe spontaneous fission (SF) is the necessity to explicitly treat the evolution as a quantum dynamic in collective space. Progresses have been made with the Time-Dependent Generator Coordinate Method (TDGCM) [12][13][14]. This theory by treating quantally collective degrees of freedom (DOF) is promising. However, the adiabatic assumption often made becomes critical especially close to scission [15]. Dissipation of the collective motion into internal excitations also plays a key role to understand the excitation energy and kinetic energy sharing during fragments separation [16]. Understanding this dissipation requires to include many-body states beyond the adiabatic limit [17]. It is yet unclear how the pre-scission neutron and proton emissions can be incorporated in the TDGCM.The nuclear time-dependent DFT (TDDFT) overcomes some of these limitations. With recently developed symmetry unrest...

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“…[41]. Although the stochastic mean-field technique was applied to simple models [37][38][39]42] or to obtain expressions of transport coefficients [40,[43][44][45][46], we present here the first application to a realistic physical phenomena where the phasespace sampling is explicitly made.…”

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Microscopic Phase-Space Exploration Modeling ofFm258Spontaneous Fission

2017

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“…[14] to describe small superfluid systems and shown to be competitive with most recent NEGF theories applied to lattice systems in Ref. [15].…”

Section: Introductionmentioning

confidence: 99%

“…This has been misleadingly interpreted in Refs. [13][14][15] as a generic defect of SMF. These two figures clearly demonstrate that this overdamping can disappear simply by changing the initial distribution.…”

Section: B Initial Phase-space Associated To Coherent and Correlatedmentioning

confidence: 99%

Importance of realistic phase-space representations of initial quantum fluctuations using the stochastic mean-field approach for fermions

2014

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In the stochastic mean-field (SMF) approach, an ensemble of initial values for a selected set of one-body observables is formed by stochastic sampling from a phase-space distribution that reproduces the initial quantum fluctuations. Independent mean-field evolutions are performed with each set of initial values followed by averaging over the resulting ensemble. This approach has been recently shown to be rather versatile and accurate in describing the correlated dynamics beyond the independent particle picture. In the original formulation of SMF, it was proposed to use a Gaussian assumption for the phase-space distribution. This assumption turns out to be rather effective when the dynamics of an initially uncorrelated state is considered, which was the case in all applications of this approach up to now. Using the Lipkin-Meshkov-Glick (LMG) model, we show that such an assumption might not be adequate if the quantum system under interest is initially correlated and presents configuration mixing between several Slater determinants. In this case, a more realistic description of the initial phase-space is necessary. We show that the SMF approach can be advantageously combined with standard methods to describe phase-space in quantum mechanics. As an illustration, the Husimi distribution function is used here to obtain a realistic representation of the phase-space of a quantum many-body system. This method greatly improves the description of initially correlated fermionic many-body states. In the LMG model, while the Gaussian approximation failed to describe these systems in all interaction strength range, the novel approach gives a perfect agreement with the exact evolution in the weak coupling regime and significantly improves the description of correlated systems in the strong coupling regime.

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“…The lowest order for the correlation selfenergy is given by the second order Born (2B) approximation. The relaxation dynamics of finite Hubbard clusters in nonequilibrium revealed [24,27,30] that the Born approximation works well for weak coupling, U 0.1. For larger coupling, the simulations have a limited time range where they are valid that shrinks as U −1 .…”

Section: Nonequilibrium Green Functions T-matrix Approximationmentioning

confidence: 99%

Toward a Nonequilibrium Green Functions Approach to Diffusion in Strongly Coupled Finite Quantum Systems

Bönitz

Schlünzen

Hermanns

2014

Contrib. Plasma Phys.

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Transport properties of strongly correlated quantum systems are of central interest in condensed matter, ultracold atoms and in dense plasmas. There, the proper treatment of strong correlations poses a great challenge to theory. Here, we apply a Nonequilibrium Green Functions approach using a lattice model as a basic system. This allow us to treat a finite spatially inhomogeneous system with an arbitrary nonequilibrium initial state. Placing all particles initially to one side of the system allows for a nonequilibrium study of diffusion. Strong correlation effects are incorporated via T‐matrix selfenergies. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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Ultrafast dynamics of finite Hubbard clusters: A stochastic mean-field approach

Cited by 43 publications

References 33 publications

Microscopic Phase-Space Exploration Modeling ofFm258Spontaneous Fission

Microscopic Phase-Space Exploration Modeling ofFm258Spontaneous Fission

Importance of realistic phase-space representations of initial quantum fluctuations using the stochastic mean-field approach for fermions

Toward a Nonequilibrium Green Functions Approach to Diffusion in Strongly Coupled Finite Quantum Systems

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