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M. Bonitz

Publications and source records attributed to M. Bonitz.

At least 127 records · Page 7Linked to original sources
arXiv2007

Invariance of the Kohn (sloshing) mode in a conserving theory

It is proven that the center of mass (COM or Kohn) oscillation of a many-body system in a harmonic trap coincides with the motion of a single particle as long as conserving approximations are applied to treat the interactions. The two conditions formulated by Kadanoff and Baym \cite{kb-book} are shown to be sufficient to preserve the COM mode. The result equally applies to zero and finite temperature, as well as to nonequilibrium situations, and to the linear and nonlinear response regimes.

cond-mat.stat-mech↗
arXiv2007

Correlation effects in partially ionized mass asymmetric electron-hole plasmas

The effects of strong Coulomb correlations in dense three-dimensional electron-hole plasmas are studied by means of unbiased direct path integral Monte Carlo simulations. The formation and dissociation of bound states, such as excitons and bi-excitons is analyzed and the density-temperature region of their appearance is identified. At high density, the Mott transition to the fully ionized metallic state (electron-hole liquid) is detected. Particular attention is paid to the influence of the hole to electron mass ratio $M$ on the properties of the plasma. Above a critical value of about M=80 formation of a hole Coulomb crystal was recently verified [Phys. Rev. Lett. {\bf 95}, 235006 (2005)] which is supported by additional results. Results are related to the excitonic phase diagram of intermediate valent Tm[Se,Te], where large values of $M$ have been observed experimentally.

cond-mat.str-el↗
arXiv2006

Crystallization in mass-asymmetric electron-hole bilayers

We consider a \textit{mass-asymmetric} electron and hole bilayer. Electron and hole Coulomb correlations and electron and hole quantum effects are treated on first princles by path integral Monte Carlo methods. For a fixed layer separation we vary the mass ratio $M$ of holes and electrons between 1 and 100 and analyze the structural changes in the system. While, for the chosen density, the electrons are in a nearly homogeneous state, the hole arrangement changes from homogeneous to localized, with increasing $M$ which is verified for both, mesoscopic bilayers in a parabolic trap and for a macroscopic system.

cond-mat.mes-hall↗
arXiv2006

Ground state of a confined Yukawa plasma

The ground state of an externally confined one-component Yukawa plasma is derived analytically. In particular, the radial density profile is computed. The results agree very well with computer simulations on three-dimensional spherical Coulomb crystals. We conclude in presenting an exact equation for the density distribution for a confinement potential of arbitrary geometry.

physics.plasm-ph↗
arXiv2006

Path integral Monte Carlo calculations of helium and hydrogen-helium plasma thermodynamics and of the deuterium shock Hugoniot

In this work we calculate the thermodynamic properties of hydrogen-helium plasmas with different mass fractions of helium by the direct path integral Monte Carlo method. To avoid unphysical approximations we use the path integral representation of the density matrix. We pay special attention to the region of weak coupling and degeneracy and compare the results of simulation with a model based on the chemical picture. Further with the help of calculated deuterium isochors we compute the shock Hugoniot of deuterium. We analyze our results in comparison with recent experimental and calculated data on the deuterium Hugoniot.

physics.plasm-ph↗
arXiv2005

Hole crystallization in semiconductors

When electrons in a solid are excited to a higher energy band they leave behind a vacancy (hole) in the original band which behaves like a positively charged particle. Here we predict that holes can spontaneously order into a regular lattice in semiconductors with sufficiently flat valence bands. The critical hole to electron effective mass ratio required for this phase transition is found to be of the order of 80.

cond-mat.str-el↗
arXiv2005

Crystallization in two-component Coulomb systems

The analysis of Coulomb crystallization is extended from one-component to two-component plasmas. Critical parameters for the existence of Coulomb crystals are derived for both classical and quantum crystals. In the latter case, a critical mass ratio of the two charged components is found which is of the order of 80. Thus, holes in semiconductors with sufficiently flat valence bands are predicted to spontaneously order into a regular lattice. Such hole crystals are intimately related to ion Coulomb crystals in white dwarf and neutron stars as well as to ion crystals produced in the laboratory. A unified phase diagram of two-component Coulomb crystals is presented and is verified by first-principle computer simulations.

cond-mat.str-el↗
arXiv2005

Ground and excited states of the bipolaron in two and three dimensions

The properties of large bipolarons in two and three dimensions are investigated by averaging over the relative wavefunction of the two electrons and using the Lee-Low-Pines-Huybrechts variational method. We obtain the ground-state (GS) and excited-state energies of the Fröhlich bipolaron for the whole range of electron-phonon coupling constants. Furthermore, we calculate the energies of the first relaxed excited state (RES) and Franck-Condon (FC) excited state of the bipolaron. Compared with the FC state, the first RES has a lower energy. Our results for the GS and RES energies are lower than those obtained before by the Landau-Pekar method in the whole coupling regime.

cond-mat.str-el↗
arXiv2005

Structural properties of screened Coulomb balls

Small three-dimensional strongly coupled charged particles in a spherical confinement potential arrange themselves in a nested shell structure. By means of experiments, computer simulations and theoretical analysis, it is shown that their structural properties depend on the type of interparticle forces. Using an isotropic Yukawa interaction, quantitative agreement for shell radii and occupation is obtained.

physics.plasm-ph↗
arXiv2005

Exciton formation and dissociation in mass-asymmetric electron-hole plasmas

First-principle path integral Monte Carlo simulations were performed in order to analyze correlation effects in complex electron-hole plasmas, particularly with regard to the appearance of excitonic bound states. Results are discussed in relation to exciton formation in unconventional semiconductors with large electron hole mass asymmetry.

cond-mat.str-el↗
arXiv2004

Structure of mesoscopic Coulomb balls

An analysis of the structural properties of three-dimensional Coulomb clusters confined in a spherical parabolic trap is presented. Based on extensive high accuracy computer simulations the shell configurations and energies for particle numbers in the range $60 \le N\le 160$ are reported. Further, the intrashell symmetry and the lowest metastable configurations are analyzed for small clusters and a novel type of excited state which does not involve a change of shell configuration is identified.

physics.plasm-ph↗
arXiv2004

Tables of mesoscopic 3D Coulomb balls

Detailed numerical results for the structural properties of three-dimensional classical Coulomb clusters confined in a spherical parabolic trap are presented. Based on extensive high accuracy computer simulations the shell configurations and energies for particle numbers in the range $2 \le N\le 160$ are reported. Further, the mean shell radii and shell widths are calculated.

physics.plasm-ph↗
arXiv2004

Monte Carlo results for the hydrogen Hugoniot

We propose a theoretical Hugoniot obtained by combining results for the equation of state (EOS) from the Direct Path Integral Monte Carlo technique (DPIMC) and those from Reaction Ensemble Monte Carlo (REMC) simulations. The main idea of such proposal is based on the fact that DPMIC provides first-principle results for a wide range of densities and temperatures including the region of partially ionized plasmas. On the other hand, for lower temperatures where the formation of molecules becomes dominant, DPIMC simulations become cumbersome and inefficient. For this region it is possible to use accurate REMC simulations where bound states (molecules) are treated on the Born-Oppenheimer level using a binding potential calculated by Kolos and Wolniewicz. The remaining interaction is then reduced to the scattering between neutral particles which is reliably treated classically applying effective potentials. The resulting Hugoniot is located between the experimental values of Knudson {\textit{et al.}} \cite{1} and Collins {\textit{et al.}} \cite{2}.

physics.plasm-ph↗
arXiv2004

Influence of well width fluctuations on the binding energy of excitons, charged excitons and biexcitons in GaAs-based quantum wells

We present a first-principle path integral Monte-Carlo (PIMC) study of the binding energy of excitons, trions (positively and negatively charged excitons) and biexcitons bound to single-island interface defects in quasi-two-dimensional GaAs/Al$_{x}$Ga$_{1-x}$As quantum wells. We discuss in detail the dependence of the binding energy on the size of the well width fluctuations and on the quantum-well width. The numerical results for the well width dependence of the exciton, trions and biexciton binding energy are in good quantitative agreement with the available experimental data.

cond-mat.mes-hall↗
arXiv2004

Temperature-dependent quantum pair potentials and their application to dense partially ionized hydrogen plasmas

Extending our previous work \cite{filinov-etal.jpa03ik} we present a detailed discussion of accuracy and practical applications of finite-temperature pseudopotentials for two-component Coulomb systems. Different pseudopotentials are discussed: i) the diagonal Kelbg potential, ii) the off-diagonal Kelbg potential iii) the {\em improved} diagonal Kelbg potential, iv) an effective potential obtained with the Feynman-Kleinert variational principle v) the ``exact'' quantum pair potential derived from the two-particle density matrix. For the {\em improved} diagonal Kelbg potential a simple temperature dependent fit is derived which accurately reproduces the ``exact'' pair potential in the whole temperature range. The derived pseudopotentials are then used in path integral Monte Carlo (PIMC) and molecular dynamics (MD) simulations to obtain thermodynamical properties of strongly coupled hydrogen. It is demonstrated that classical MD simulations with spin-dependent interaction potentials for the electrons allow for an accurate description of the internal energy of hydrogen in the difficult regime of partial ionization down to the temperatures of about $60 000$ K. Finally, we point out an interesting relation between the quantum potentials and effective potentials used in density functional theory.

cond-mat.stat-mech↗
arXiv2002

Interacting electrons in a one-dimensional random array of scatterers - A Quantum Dynamics and Monte-Carlo study

The quantum dynamics of an ensemble of interacting electrons in an array of random scatterers is treated using a new numerical approach for the calculation of average values of quantum operators and time correlation functions in the Wigner representation. The Fourier transform of the product of matrix elements of the dynamic propagators obeys an integral Wigner-Liouville-type equation. Initial conditions for this equation are given by the Fourier transform of the Wiener path integral representation of the matrix elements of the propagators at the chosen initial times. This approach combines both molecular dynamics and Monte Carlo methods and computes numerical traces and spectra of the relevant dynamical quantities such as momentum-momentum correlation functions and spatial dispersions. Considering as an application a system with fixed scatterers, the results clearly demonstrate that the many-particle interaction between the electrons leads to an enhancement of the conductivity and spatial dispersion compared to the noninteracting case.

cond-mat.dis-nn↗
arXiv2001

Single-electron control of Wigner crystallization

Wigner crystallization in mesoscopic quantum dots containing only few ($N < 50$) electrons exhibits a number of interesting peculiarities: (i) there exist two distinct crystal phases, and (ii) the phase boundary sensitively depends on the precise particle number. In this paper we demonstrate that this behavior can be used to control the {\em collective} transport properties by adding or removing a {\em single electron}.

cond-mat.mes-hall↗