Regensburg 2002 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 22: Postersitzung III: Syst. korr. Elektr.: Theorie II (1-15), Metall-Isol.- und Phasenüberg
änge (16-33), SL: Massivmat., Bandl., Pinning, Vortexdyn., Transport, Korngr. (34-43), Niedrigdim. Syst., Magnetotransport (44-63)

TT 22.14: Poster

Donnerstag, 14. März 2002, 14:00–17:30, A

Magnetism, superconductivity and non-Fermi-liquid behavior of 2D systems owing to van Hove singularities — •Andrey Katanin1,2, Valentin Irkhin2, and Mikhail Katsnelson21Institute fur Physik, Theoretische Physik III, Universitat Augsburg, 86135 Augsburg, Germany — 2Institute of Metal Physics, Kovalevskaya st., 18, 620219, Ekaterinburg, Russia

We consider the problem of the influence of van Hove singularities (VHS) on magnetism and superconductivity of 2D systems. This problem is important for high-Tc superconductors where van Hove singularities are close to the Fermi surface. We consider the tt Hubbard model (t<0). The phase diagram of this model near van Hove band filling is investigated within the parquet approach and two-patch approximation. For small t/t we find the antiferromagnetic instability, while for |t/t| close to 1/2 we obtain ferromagnetic ordering. At intermediate values of t/t the d-wave superconducting state occurs. The stability of antiferro- and especially ferromagnetic phase is greatly reduced in comparison with the corresponding mean-field criteria, which demonstrates that mean-field treatment of such systems is completely inapplicable.

The electron self-energy has a nearly-linear energy dependence far from QPT into magnetically ordered or superconducting phase. Close to QPT the real part of the self-energy has pronounced peak at small energies ε ∼ |µ | and the quasiparticle dispersion acquires the flat part. It is shown also that in a broad range of fillings the Fermi surface which is obtained with the account of electron interaction is pinned to van Hove singularities.

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