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TT: Tiefe Temperaturen

TT 8: Mesoskopische Systeme

TT 8.7: Talk

Tuesday, March 27, 2001, 11:45–12:00, A

Symmetry Adapted BCS-Type Trial Functions for Mesoscopic Rings — •Ioan Baldea^1,2, Horst Köppel², and Lorenz S. Cederbaum² — ¹Physikalisches Institut, Universität Karlsruhe, 76128 Karlsruhe — ²Theoretische Chemie, Physikalisch-Chemisches Institut, Universität Heidelberg, INF 229, 69120 Heidelberg

In mesoscopic systems, the symmetry of the wave function cannot be broken and must be considered. We construct symmetry adapted trial wave functions of BCS type for mesoscopic rings described by an extended Hubbard model at half filling. The comparison with exact numerical (Lanczos) diagonalization in small rings indicates that this variational approach is reasonably accurate. Within this aproach, we demonstrate a crossover from a weak correlation regime to a strong correlation one. Particularly interesting is the behavior of the lowest excitation energy, which switches from a HOMO-LUMO gap to a splitting energy related to a collective tunneling of electrons.