Regensburg 2002 – wissenschaftliches Programm

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M: Metallphysik

M 11: Quasikristalle IV

M 11.1: Fachvortrag

Dienstag, 12. März 2002, 16:30–16:45, H6

Structure Formation at Early Stages Decribed as an Effect of Optimized Resonances between Subsystems — •P. Häussler and J. Barzola-Quiquia — Institut für Physik, Technische Univ. Chemnitz, 09107 Chemnitz

Any sort of structure starts to evolve from the disordered state. Under the given restrictrons, in this state the total system finds many ways to optimize the total energy. In recent years it became clear that disordered metals and semiconductors, as well as ionic glasses show structure formation under the influence of resonances between subsystems like all the valence electrons together as one of them and the forming static structure as the other. Gaps or pseudogaps get formed at the Fermi energy which are stabilizing the phase. Resonances based on momentum transfer between the subsystems cause spherical-periodic order at short- and medium-range distances which are strongly interpenetrating each other. Resonances based on angular-momentum transfer, in addition, cause angular correlations, enhancing the stability of the phase even further. By annealing the amorphous quasicrystals, the resonances get more pronounced and, finally, extending angular correlation triggers the formation of the quasicrystalline state.

In order to optimize the resonance, besides the adjustement of the atomic sites, the electronic subsystem may also adjust by varying the electronic density via charge transfer, correlated to changes of the atomic volume, as well as via hybridisation effects, correlated to variations of the effective valency.