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MA: Fachverband Magnetismus

MA 3: Bio- and Molecular Magnetism

MA 3.1: Talk

Monday, March 14, 2011, 11:00–11:15, HSZ 401

Transition from the Quantum to the Classical Limit for the Antiferromagnetic Heisenberg Model on the Icosahedron — •Nikolaos P. Konstantinidis — Physikalisches Institut, Universität Freiburg, 79104 Freiburg, Germany

The antiferromagnetic Heisenberg model on the icosahedron, which consists of 20 triangles and belongs to the icosahedral I_h symmetry group, presents unconventional properties at the quantum and classical level. These originate in the frustrated nature of the interactions between the spins. In the quantum limit, there are non-magnetic excitations within the singlet-triplet gap and the specific heat has a multi-peak structure as a function of temperature [1]. For classical spins, the magnetization is discontinuous as a function of an external magnetic field [2]. Here the transition from the full quantum s_i=1/2 to the classical limit is investigated by progressively increasing s_i and focusing on the low-energy spectrum and the magnetization in an external field. The icosahedral I_h symmetry properties of the model are fully taken into account in the characterization of the states and show how the quantum fluctuations yield to the classical properties as s_i is increased.

[1] N. P. Konstantinidis, Phys. Rev. B 72, 064453 (2005).

[2] C. Schröder et al., Phys. Rev. Lett. 94, 207203 (2005).