Regensburg 2002 – wissenschaftliches Programm

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MA: Magnetismus

MA 19: Spinstrukturen und magnetische Phasenübergänge (incl. Sensoren(19.11) und Messmethoden(19.12-13))

MA 19.10: Vortrag

Donnerstag, 14. März 2002, 17:30–17:45, H23

Absence of Spontaneous Magnetic Order at Nonzero Temperature in One- and Two-Dimensional Heisenberg and XY Systems with Long-Range Interactions — •Patrick Bruno — Max-Planck-Institut für Mikrostruturphysik, Weinberg 2, O6120 Halle, Germany

The Mermin-Wagner theorem is strengthened so as to rule out magnetic long-range order at T>0 in one- or two-dimensional Heisenberg and XY systems with long-range interactions decreasing as R^−α with a sufficiently large exponent α [1]. For oscillatory interactions, ferromagnetic long-range order at T>0 is ruled out if α ≥ 1 (D = 1) or α >5/2 (D = 2). For systems with monotonically decreasing interactions, ferro- or antiferromagnetic long-range order at T>0 is ruled out if α ≥ 2D.
[1] P. Bruno, Phys. Rev. Lett. 87, 137203 (2001).