arXiv subjects

M. Bonitz

Publications and source records attributed to M. Bonitz.

At least 73 records · Page 4Linked to original sources

arXiv2012

Magnetized strongly coupled plasmas and how to realize them in a dusty plasma setup

Strongly coupled plasmas in which the interaction energy exceeds the kinetic energy play an important role in many astrophysical and laboratory systems including compact stars, laser plasmas and dusty plasmas. They exhibit many unusual collective properties, such as liquid or crystalline behaviour, peculiar oscillation spectra and transport properties. Recently, strongly coupled plasmas were studied in the presence of a strong magnetic field by computer simulations, and strong modifications of their transport properties and oscillation spectra were observed. While strong magnetization is common in stellar systems it is practically impossible to achieve in complex plasmas due to the large mass of the dust particles. Here we discuss a recently demonstrated approach to achieve very strong "magnetization" by a rotation of the neutral gas, and we present new results for macroscopic two-dimensional systems.

physics.plasm-ph↗

arXiv2012

Magnetizing a complex plasma without a magnetic field

We propose and demonstrate a concept that mimics the magnetization of the heavy dust particles in a complex plasma while leaving the properties of the light species practically unaffected. It makes use of the frictional coupling between a complex plasma and the neutral gas, which allows to transfer angular momentum from a rotating gas column to a well-controlled rotation of the dust cloud. This induces a Coriolis force that acts exactly as the Lorentz force in a magnetic field. Experimental normal mode measurements for a small dust cluster with four particles show excellent agreement with theoretical predictions for a magnetized plasma.

physics.plasm-ph↗

arXiv2012

Non-equilibrium Green's function approach to inhomogeneous quantum many-body systems using the Generalized Kadanoff Baym Ansatz

In non-equilibrium Green's function calculations the use of the Generalized Kadanoff-Baym Ansatz (GKBA) allows for a simple approximate reconstruction of the two-time Green's function from its time-diagonal value. With this a drastic reduction of the computational needs is achieved in time-dependent calculations, making longer time propagation possible and more complex systems accessible. This paper gives credit to the GKBA that was introduced 25 years ago. After a detailed derivation of the GKBA, we recall its application to homogeneous systems and show how to extend it to strongly correlated, inhomogeneous systems. As a proof of concept, we present results for a 2-electron quantum well, where the correct treatment of the correlated electron dynamics is crucial for the correct description of the equilibrium and dynamic properties.

cond-mat.str-el↗

arXiv2012

Theoretical description of field-assisted post-collision interaction in Auger decay of atoms

In a recent publication [B. Schuette, S. Bauch et al., accepted for publication in Phys. Rev. Lett. 2012] it was demonstrated both, experimentally and theoretically, that Auger electrons are subject to an energetic chirp if a three-body-interaction dubbed post-collision interaction (PCI) is involved. Here, we extend previous theoretical work and give a detailed analysis of field-assisted PCI based on numerical solutions of the time-dependent Schrödinger equation, extensive Monte-Carlo averaged molecular dynamics simulations and analytical theory. The dependence on various streaking and excitation conditions is investigated, and we discuss, how these findings may help to improve XUV pulse characterization as well as understanding of ultrafast atomic processes.

physics.atom-ph↗

arXiv2012

Electronic double-excitations in quantum wells: solving the two-time Kadanoff-Baym equations

For a quantum many-body system, the direct population of states of double-excitation character is a clear indication that correlations importantly contribute to its nonequilibrium properties. We analyze such correlation-induced transitions by propagating the nonequilibrium Green's functions in real-time within the second Born approximation. As crucial benchmarks, we compute the absorption spectrum of few electrons confined in quantum wells of different width. Our results include the full two-time solution of the Kadanoff-Baym equations as well as of their time-diagonal limit and are compared to Hartree-Fock and exact diagonalization data.

cond-mat.str-el↗

arXiv2012

Color path-integral Monte Carlo simulations of quark-gluon plasma

Thermodynamic properties of a strongly coupled quark-gluon plasma (QGP) of constituent quasiparticles are studied by a color path-integral Monte Carlo simulations (CPIMC). For our simulations we have presented QGP partition function in the form of color path integral with new relativistic measure instead of Gaussian one used in Feynman and Wiener path integrals. For integration over color variable we have also developed procedure of sampling color variables according to the group SU(3) Haar measure. It is shown that this method is able to reproduce the available quantum lattice chromodynamics (QCD) data.

hep-ph↗

arXiv2011

Oscillation Spectrum of a Magnetized Strongly Coupled One-Component-Plasma

A first-principle study of the collective oscillation spectrum of a strongly correlated one-component plasma in a strong magnetic field is presented. The spectrum consists of six fundamental modes which are found to be in good agreement with results from the Quasi-Localized Charge approximation. At high frequencies additional modes are observed that include Bernstein-type oscillations and their transverse counterparts which are of importance for the high-frequency optical and transport properties of these plasmas.

physics.plasm-ph↗

arXiv2011

Diffusion and growth of metal clusters in nanocomposites: a Kinetic Monte Carlo study

Nobel metals that are deposited on a polymer surface exhibit surface diffusion and diffusion into the bulk. At the same time the metal atoms tend to form clusters because their cohesive energy is about two orders of magnitude higher than the cohesive energy of polymers. To selfconsistently simulate these coupled processes, we present in this paper a Kinetic Monte Carlo approach. Using a simple model with diffusion coefficients taken as input parameters allows us to perform a systematic study of the behavior of a large ensemble of metal atoms on a polymer surface eventually leading to polymer nanocomposites. Special emphasis is placed on the cluster growth, cluster size distribution and the penetration of clusters into the substrate. We also study the influence of surface defects and analyze how the properties of the resulting material can be controlled by variation of the deposition rate.

physics.plasm-ph↗

arXiv2011

Diffusion in a strongly coupled magnetized plasma

A first-principle study of diffusion in a strongly coupled one-component plasma in a magnetic field B is presented. As in a weakly coupled plasma, the diffusion coefficient perpendicular to the field exhibits a Bohm-like 1/B-behavior in the strong-field limit, but its overall scaling is substantially different. The diffusion coefficient parallel to the field is strongly affected by the field as well and also approaches a 1/B scaling, in striking contrast to earlier predictions.

physics.plasm-ph↗

arXiv2011

Crystallization of an exciton superfluid

Indirect excitons -- pairs of electrons and holes spatially separated in semiconductor bilayers or quantum wells -- are known to undergo Bose-Einstein condensation and to form a quantum fluid. Here we show that this superfluid may crystallize upon compression. However, further compression results in quantum melting back to a superfluid. This unusual behavior is explained by the effective interaction potential between indirect excitons which strongly deviates from a dipole potential at small distances due to many-particle and quantum effects. Based on first principle path integral Monte Carlo simulations, we compute the complete phase diagram of this system and predict the relevant parameters necessary to experimentally observe exciton crystallization in semiconductor quantum wells.

cond-mat.quant-gas↗

arXiv2011

Higher Harmonics Generation in Strongly Coupled Magnetized Two-Dimensional Yukawa Liquids

The excitation spectra of two-dimensional strongly coupled (liquid-like) Yukawa systems under the influence of a magnetic field perpendicular to the plane are found to sustain additional high-frequency modes at multiples of the magnetoplasmon. These modes are reminiscent of the well-known Bernstein modes but show a number of important differences due to the strong coupling of the particles.

physics.plasm-ph↗

arXiv2011

Quantum simulations of thermodynamic properties of strongly coupled quark-gluon plasma

A strongly coupled quark-gluon plasma (QGP) of heavy constituent quasi-particles is studied by a path-integral Monte-Carlo method. This approach is a quantum generalization of the model developed by Gelman, Shuryak and Zahed. It is shown that this method is able to reproduce the QCD lattice equation of state and also yields valuable insight into the internal structure of the QGP. The results indicate that the QGP reveals liquid-like rather than gas-like properties. At temperatures just above the critical one it was found that bound quark-antiquark states still survive. These states are bound by effective string-like forces and turns out to be colorless. At the temperature as large as twice the critical one no bound states are observed. Quantum effects turned out to be of prime importance in these simulations.

nucl-th↗

arXiv2010

Higher harmonics of the magnetoplasmon in strongly coupled Coulomb and Yukawa systems

The generation of higher harmonics of the magnetoplasmon frequency which has recently been reported in strongly coupled two-dimensional Yukawa systems is investigated in detail and, in addition, extended to two-dimensional Coulomb systems. We observe higher harmonics over a much larger frequency range than before and compare the theoretical prediction with the simulations. The influence of the coupling, structure, and thermal energy on the excitation of these modes is examined in detail. We also report on the effect of friction on the mode spectra to make predictions about the experimental observability of this new effect.

physics.plasm-ph↗

arXiv2010

Collective excitations of a spherically confined Yukawa plasma

The results of a recent fluid theory for the multipole modes of a Yukawa plasma in a spherical confinement [H. Kählert and M. Bonitz, Phys. Rev. E \textbf{82}, 036407 (2010)] are compared with molecular dynamics simulations and the exact $N$-particle eigenmodes in the crystalline phase. Simulations confirm the existence of high order modes found in cold fluid theory. We investigate the influence of screening, coupling and friction on the mode spectra in detail. Good agreement between theory and simulation is found for weak to moderate screening and low order modes. The relations between the breathing mode in the fluid theory, simulation and the crystal eigenmode are investigated in further detail.

physics.plasm-ph↗

arXiv2010

Quantum simulations of strongly coupled quark-gluon plasma

A strongly coupled quark-gluon plasma (QGP) of heavy constituent quasiparticles is studied by a path-integral Monte-Carlo method, which improves the corresponding classical simulations by extending them to the quantum regime. It is shown that this method is able to reproduce the lattice equation of state and also yields valuable insight into the internal structure of the QGP. The results indicate that the QGP reveals liquid-like rather than gas-like properties. At temperatures just above the critical one it was found that bound quark-antiquark states still survive. These states are bound by effective string-like forces. Quantum effects turned out to be of prime importance in these simulations.

nucl-th↗

arXiv2010

Effective coupling parameter for 2D Yukawa liquids and non-invasive measurement of plasma parameters

We derive an effective coupling parameter for two-dimensional Yukawa systems based on the height of the first maximum of the pair distribution function. Two variants -- one valid in the high-coupling range, the other for arbitrary couplings of the liquid -- are derived. Comparison to previous approaches to Yukawa coupling parameters shows that the present concept is more general and more accurate. Using, in addition, dynamical information contained in the velocity autocorrelation function, we outline a reference data method that can be employed as a non-invasive measurement scheme of the plasma parameters -- the coupling strength and the screening length. This approach requires only input from a time-series of configuration snapshots and particle velocities with no recourse to additional information about the system. Our results should be directly applicable as a simple, yet reliable diagnostic method for a variety of experiments, including dusty plasmas, colloidal suspensions and ions in traps, and can be employed to facilitate comparisons between experiments, theory and simulations.

physics.plasm-ph↗

arXiv2010

Two-photon ionization of Helium studied with the multiconfigurational time-dependent Hartree-Fock method

The multiconfigurational time-dependent Hartree-Fock method (MCTDHF) is applied for simulations of the two-photon ionization of Helium. We present results for the single- and double ionization from the groundstate for photon energies in the non-sequential regime, and compare them to direct solutions of the Schrödinger equation using the time-dependent (full) Configuration Interaction method (TDCI). We find that the single-ionization is accurately reproduced by MCTDHF, whereas the double ionization results correctly capture the main trends of TDCI.

physics.atom-ph↗

arXiv2010

Time-dependent second Born calculations for model atoms and molecules in strong laser fields

Using the finite-element discrete variable representation of the nonequilibrium Green's function (NEGF) we extend previous work [K.~Balzer et al., Phys. Rev. A \textbf{81}, 022510 (2010)] to nonequilibrium situations and compute---from the two-time Schwinger-Keldysh-Kadanoff-Baym equations---the response of the helium atom and the heteronuclear molecule lithium hydride to laser fields in the uv and xuv regime. In particular, by comparing the one-electron density and the dipole moment to time-dependent Hartree-Fock results on one hand and the full solution of the time-dependent Schrödinger equation on the other hand, we demonstrate that the time-dependent second Born approximation carries valuable information about electron-electron correlation effects. Also, we outline an efficient distributed memory concept which enables a parallel and well scalable algorithm for computing the NEGF in the two-time domain.

physics.atom-ph↗