Physics – Condensed Matter – Superconductivity
Scientific paper
2010-04-12
J. Phys.: Condens. Matter 22 203203 (2010)
Physics
Condensed Matter
Superconductivity
To be published as a topical review for Journal of Physics: Condensed Matter (13 figures)
Scientific paper
10.1088/0953-8984/22/20/203203
In this review, we present a summary of experimental studies of magnetism in Fe-based superconductors. The doping dependent phase diagram shows strong similarities to the generic phase diagram of the cuprates. Parent compounds exhibit magnetic order together with a structural phase transition both of which are progressively suppressed with doping allowing superconductivity to emerge. The stripe-like spin arrangement of Fe moments in the magnetically ordered state shows the identical in-plane structure for the RFeAsO (R=rare earth) and AFe2As2 (A=Sr, Ca, Ba, Eu and K) parent compounds, notably different than the spin configuration of the cuprates. Interestingly, Fe1+yTe orders with a different spin order despite very similar Fermi surface topology. Studies of the spin dynamics in the parent compounds shows that the interactions are best characterized as anisotropic three-dimensional (3D) interactions. Despite the room temperature tetragonal structure, analysis of the low temperature spin waves under the assumption of a Heisenberg Hamiltonian indicates strong in-plane anisotropy with a significant next-near neighbor interaction. In the superconducting state, a resonance, localized in both wavevector and energy is observed in the spin excitation spectrum as in the cuprates. This resonance is observed at a wavevector compatible with a Fermi surface nesting instability independent of the magnetic ordering of the relevant parent compound. The resonance energy (Er) scales with superconducting transition temperature (TC) as Er ~4.9 kBTC consistent with the canonical value of ~5 kBTC observed in the cuprates. Moreover, the relationship between the resonance energy and the superconducting gap, \Delta, is similar to that observed in many unconventional superconductors (Er/2\Delta ~ 0.64).
Christianson Andrew D.
Lumsden Mark D.
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