80 research outputs found
Phase Transition in Strongly Degenerate Hydrogen Plasma
Direct fermionic path-integral Monte-Carlo simulations of strongly coupled
hydrogen are presented. Our results show evidence for the hypothetical plasma
phase transition. Its most remarkable manifestation is the appearance of
metallic droplets which are predicted to be crucial for the electrical
conductivity allowing to explain the rapid increase observed in recent shock
compression measurments.Comment: 1 LaTeX file using jetpl.cls (included), 5 ps figures. Manuscript
submitted to JETP Letter
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.Comment: accepted for publication in J. Phys. A: Math. Ge
Thermodynamic Properties of Correlated Strongly Degenerate Plasmas
An efficient numerical approach to equilibrium properties of strongly coupled
systems which include a subsystem of fermionic quantum particles and a
subsystem of classical particles is presented. It uses an improved path
integral representation of the many-particle density operator and allows to
describe situations of strong coupling and strong degeneracy, where analytical
theories fail. A novel numerical method is developed, which allows to treat
degenerate systems with full account of the spin scatistics. Numerical results
for thermodynamic properties such as internal energy, pressure and pair
correlation functions are presented over a wide range of degeneracy parameter.Comment: 8 pages, 4 figures, uses sprocl.sty (included) to be published in
"Progress in Nonequilibrium Green's functions", M. Bonitz (Ed.), World
Scientific 200
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.Comment: 10 pages and 8 figures, to appear in PRB April 1
Effective interaction potential and superfluid-solid transition of spatially indirect excitons
Using an adiabatic approximation we derive an effective interaction
potentially for spatially indirect excitons. Using this potential and path
integral Monte Carlo simulations we study exciton crystllization and the
quantum melting phase transition in a macroscopic system of 2D excitons.
Furthermore, the superfluid fraction is calculated as a function of density and
shown to vanish upon crystallization. We show that the commonly used dipole
model fails to correctly describe indirect excitons in quantum well structures
Path integral Monte Carlo simulation of charged particles in traps
This chapter is devoted to the computation of equilibrium (thermodynamic)
properties of quantum systems. In particular, we will be interested in the
situation where the interaction between particles is so strong that it cannot
be treated as a small perturbation. For weakly coupled systems many efficient
theoretical and computational techniques do exist. However, for strongly
interacting systems such as nonideal gases or plasmas, strongly correlated
electrons and so on, perturbation methods fail and alternative approaches are
needed. Among them, an extremely successful one is the Monte Carlo (MC) method
which we are going to consider in this chapter.Comment: 18 pages, based on talks on Hareaus school on computational methods,
Greifswald, September 200
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.Comment: 8 pages, 10 figures, revised version of the contribution to
proceedings of "Int. Workshop on High Density Nuclear Matter", Cape Town,
5-10 Apr., 201
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