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TT: Tiefe Temperaturen
TT 11: Postersitzung II (Metall-Isolator-Überg
änge, Phasenüberg
änge in Quantensystemen, Theorie: Systeme korrelierter Elektronen)
TT 11.24: Poster
Dienstag, 25. März 2003, 14:30–19:00, P2c, P2d
Cyclic Carbohydrates: Nanoscopic SQUIDs? — •Markus Himmerich1, P. G. J. van Dongen1, and R. M. Noack2 — 1Institut für Physik, Johannes Gutenberg-Universität, Staudinger Weg 7, D-55099 Mainz — 2Institut für Theoretische Physik III, Universität Stuttgart, Pfaffenwaldring 57 V, D-70550 Stuttgart
We present a nonperturbative method for calculating persistent currents in nanoscopic quantum rings. Starting from the extended Hubbard model on a ring, threaded by an Aharonov-Bohm type flux, we add a feedback term through which the current can generate magnetic flux. Another additional term of the Hamiltonian describes the energy stored in the internally generated field. This model is evaluated using exact diagonalization and an iterative scheme to find the minima of the free energy with respect to the current. The results are: (1) A novel mechanism for ferromagnetism in quantum rings, analog to the one in π-SQUIDs. (2) The magnetic properties of conjugated carbohydrates like benzene can be investigated at intense external magentic flux densities.