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TT: Fachverband Tiefe Temperaturen

TT 44: Poster Session Correlated Electrons

TT 44.72: Poster

Thursday, March 17, 2011, 10:00–13:00, P1

Investigation of giant spin rings with DMRG — •Jörg Ummethum and Jürgen Schnack — Universität Bielefeld, Fakultät für Physik, Postfach 100131, D-33501 Bielefeld

Giant antiferromagnetic molecules like Fe₁₈ [1], which consists of 18 s=5/2 spins on a ring, are much too large for exact diagonalization so that simplifying models or approximate numerical methods like Quantum Monte Carlo or DMRG have to be used. For one-dimensional systems DMRG is known to yield very accurate results.

We use static and dynamical DMRG methods to investigate the low-lying spectrum of a Heisenberg spin ring consisting of 18 spins (neglecting the small single-ion anisotropy which is present in Fe₁₈) with spin quantum numbers s=1/2 and s=5/2. We calculate the lowest energies in subspaces of total magnetic quantum number, the T=0 magnetization curve, and the spectral function S^zz(q,ω) for different values of q. Since the momentum of the ground state is known, the momenta of low-lying excited states in the S=1 subspace can be calculated by looking for peaks in S^zz(q,ω).

We find that the lowest energies in subspaces of total magnetic quantum number form a rotational band and that transitions from the S=0 ground state to the S=1 ground state within the first rotational band are dominant. This agrees with the results of [2] where much smaller spin rings have been investigated using exact diagonalization.
O. Waldmann, T. C. Stamatatos, G. Christou, H. U. Güdel, I. Sheikin, and H. Mutka, Phys. Rev. Lett. 102, 157202 (2009)
O. Waldmann, Phys. Rev. B 65, 024424 (2001).