Berlin 2012 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 45: Correlated Electrons: Poster Session
TT 45.84: Poster
Donnerstag, 29. März 2012, 15:00–19:00, Poster B
ESR spectrum of the spin-1/2 Heisenberg-Ising chain — •Michael Brockmann1, Frank Göhmann1, Michael Karbach1, Andreas Klümper1, and Alexander Weiße2 — 1Bergische Universität Wuppertal, 42097 Wuppertal, Germany — 2Max-Planck-Institut für Mathematik, 53072 Bonn, Germany
We analyze the ESR absorption spectrum of the spin-1/2 Heisenberg-Ising chain, also known as XXZ chain. The moments of the absorbed intensity can be calculated exactly due to the integrability of this model. They can be used to define the shift of the resonance as well as the width of the spectral line, both induced by the anisotropy of the interactions. If the frequency of the incident microwave is varied for fixed Zeeman field, the first four moments are sufficient to explore the exact resonance shift and line width at arbitrary temperatures and Zeeman fields in the full range of anisotropy parameters. In current ESR experiments, however, the Zeeman field is varied for fixed frequency. For this case we can still present results for the shift at small anisotropies and a high-temperature expansion for the line width.
We performed numerical calculations which agree well with exact data. Additionally, we are able to extract an empirical parameter-free model for the line shape at high temperatures which is extremely accurate over a wide range of anisotropy parameters and is exact at the free-fermion point and at the isotropic point. The anisotropic model shows strong absorption even in the zero-field limit. We derive the exact two-spinon ground-state contribution to the spectral line which accounts for more than 96% of the spectral weight at moderate anisotropy.