Wednesday, November 7, 2012

Are the iron pnictide superconductors strongly correlated?

Yes. According to a nice review by Yu, Si, Goswami, and Abrahams.

A key piece of the evidence for strong correlations is recent inelastic neutron scattering experiments reported in this Nature Physics paper.
They show that even in the superconducting materials [which are doped from parent Antiferromagnetic compounds] there are sizeable fluctuating magnetic moments. The figure below shows the dynamical spin susceptibility versus energy. For both superconducting and antiferromagnetic materials the susceptibility is essentially the same for energies above 100 meV.
The area under the curve is equal to the square of the fluctuating local moment. The magnitude is a few Bohr magnetons, as one would expect in a doped Mott insulator.

Furthermore, a weak coupling RPA treatment [which is invoked to explain the superconductivity] cannot capture the magnitude of these spin fluctuations. In contrast, a DMFT treatment from Park, Haule, and Kotliar is consistent with the experimental data, highlighting the role of strong correlations and Hund's rule coupling.


  1. except for this,
    Electronic correlations in the iron pnictides
    M. M. Qazilbash, J. J. Hamlin, R. E. Baumbach, Lijun Zhang, D. J. Singh, M. B. Maple, D. N. Basov
    Journal reference: Nature Physics 5, 647 (2009)
    Cite as: arXiv:0909.0312

    and this,
    arXiv:0905.2633 [pdf, ps, other]
    Evidence for weak electronic correlations in Fe-pnictides
    W. L. Yang, P. O. Velasco, J. D. Denlinger, A. P. Sorini, C-C. Chen, B. Moritz, W.-S. Lee, F. Vernay, B. Delley, J.-H. Chu, J. G. Analytis, I. R. Fisher, Z. A. Ren, J. Yang, W. Lu, Z. X. Zhao, J. van den Brink, Z. Hussain, Z.-X. Shen, T. P. Devereaux
    Phys. Rev. B 80, 014508 (2009

  2. The main point being that probably in the 11-compounds they have stronger correlations than in like the 1111 compounds, and we cant always view the iron-SCs as all the same...

    Since Abrahams and Si and others were very early in suggestions to treat these materials as strongly correlated there possibly maybe could be self interest in promoting that perspective.