Spinons and covalency effects in one-dimensional spin-½ cuprate antiferromagnets

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• Prof. Toby Perring, Rutherford Appleton Lab
• Thursday 19 November 2009, 13:45-15:00
• Theory Library.

If you have a question about this talk, please contact Dr Dimitri M Gangardt.

The study of simple magnetic Hamiltonians and their experimental realisations in solids is a fertile activity for building an understanding of the complex many-body phenomenon of magnetism. The subject of this seminar is the one-dimensional Heisenberg antiferromaget with spin S=½, which has been studied theoretically and experimentally for almost 80 years. The chain shows no long range magnetic order, and instead of conventional spin waves the elementary excitations are pairs of defects called spinons.

The experimental results presented will centre on our recent work on an almost perfect realisation of the spin ½ Heisenberg antiferromagnetic chain in the cuprate Sr2CuO3 1. The bandwidth of the two-spinon continuum is about 0.75 eV, a significant fraction of the charge gap of about 1.4 eV. We used inelastic neutron scattering to map the spinon dynamics and quantitatively compared the data to the exact dynamical structure factor for the one-dimensional spin ½ Heisenberg Hamiltonian. Although the experimental dynamical structure factor is well described by the model, the magnetic intensity is modified dramatically by strong hybridisation of Cu 3d states with the oxygen p states. Ab initio LDA +U calculations reveal significant spin density on the oxygen sites; the resulting covalent magnetic form factor enables a full quantitative explanation for the measured dynamical structure factor. The implications of the work for an understanding of the magnetic fluctuations in the famous high-TC superconducting cuprates will be discussed.

This talk is part of the Theoretical Physics Seminars series.

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