Structure, melting, and potential barriers in mesoscopic clusters of repulsive particles |
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Authors: | Yu E Lozovik E A Rakoch |
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Institution: | (1) Institute of Spectroscopy, Russian Academy of Sciences, 142092 Troitsk, Moscow Region, Russia |
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Abstract: | This paper discusses two-dimensional mesoscopic clusters of particles that repel according to dipole, Coulomb, and logarithmic
laws and are confined by an external parabolic potential. These models describe a number of physical systems, in particular,
electrons in semiconductor structures or on a liquid-helium surface allowing for image forces, indirect excitons in coupled
semi-conductor dots, and a small number of vortices in an island of a second-order superconductor or in superfluid helium.
Two competing forms of ordering are detected in the particles in the mesoscopic clusters-the formation of a triangular lattice
or of a shell structure. The temperature dependences of the potential energy, the mean-square radial and angular deviations,
the radial and angular distributions of the particles, and the distribution of the particles over the local minima are studied.
Melting in mesoscopic clusters occurs in two stages: at lower temperatures, there is orientation melting, from the frozen
phase into a phase with rotational reorientation of “crystalline” shells with respect to each other; subsequently, a transition
occurs in which the radial order disappears. Melting in dipole macroclusters occurs in a single stage. However, in Coulomb
and logarithmic macroclusters, orientation melting occurs only for the outer pairs of shells. Orientation melting is also
detected in three-dimensional Coulomb clusters. A connection is established between the character of the melting and the ratio
of the energy barriers that describe the breakdown of the orientational and radial structure of a cluster.
Zh. éksp. Teor. Fiz. 116, 2012–2037 (December 1999) |
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