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{\Large \bf Plasma Phase Transitions in Dense Coulomb Systems}\\[2ex]

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{\large V.~Filinov$^{1}$, M.~Bonitz$^{2}$, P.~Levashov$^{1}$, V.E.~Fortov$^{1}$,
W.~Ebeling$^{3}$, M.~Schlanges$^{4}$ and S.W.~Koch$^{5}$}

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$^1$High Energy Density Center of the RAS, Moscow\\
$^{2}$FB Physik, Rostock University, D-18051 Rostock, Germany\\
$^{3}$FB Physik, Humboldt University Berlin, Germany\\
$^4$FB Physik, Universit\"at Greifswald, Germany \\
$^5$FB Physik, Philipps-Universit\"at Marburg, Germany

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%\centerline{\large Abstract}
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\noindent
Many years ago Landau, and later Norman and Starostin, predicted that the homogeneous state of a dense
partially ionized Coulomb system may become unstable at temperatures below 0.1 Ry. Since then this has
been confirmed by many authors based on chemical models for the plasma composition, [1,2].
However, in the region of this plasma phase transition (PPT) drastic changes
of the composition (Mott effect, pressure dissociation and ionization) lead to failure of the chemical picture,
and only first-principle results may give a conclusive answer. We, therefore, have performed
detailed path integral Monte Carlo (PIMC) simulations for hydrogen and hydrogen-helium mixtures [3,4]
 confirming the existence of the PPT at densities around $3\cdot 10^{23}$cm$^{-3}$.
Moreover, they allow us to give a microscopic picture of the plasma state -- it consists of dense
droplets with delocalized electrons.
As a further test, the simulations are extended to semiconductors, where similar (electron-hole)
droplet formation
is well established experimentally and theoretically. Our PIMC simulations for Ge and GaAs show good
agreement with the experiments. 




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\noindent [1] M.~Schlanges, M.~Bonitz, and A.~Tschttschjan,
Contrib. Plasma Phys. {\bf 35},  109 (1995)

\noindent [2] for a recent overview, see D.~Beule et al., Phys. Rev. B {\bf 59}, 14177 (1999 )

\noindent [3] V.~Filinov, M.~Bonitz, W.~Ebeling, and V.E.~Fortov,
Plasma Physics and Controlled Fusion {\bf 43}, 743-759 (2001)

\noindent [4] V.~Filinov, V.E.~Fortov, M.~Bonitz, and P.~Levashov,
JETP Letters {\bf 74}, 384 (2001)

%\noindent [5] S.W.~Koch

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