Consistent theory of magnetism in ferropnictides

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Date/Time:Thursday, 27 Jan 2011 - Thursday, 27 Jan 2011
Location:ROOM 5, PHYSICS
Channel:Condensed Matter Physics
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Vladimir Antropov Ames Laboratory

The discovery of superconductivity in LaFeAsO introduced the ferropnictides as a major new class of superconducting compounds with critical temperatures second only to cuprates. The presence of magnetic iron makes ferropnictides radically different from cuprates.

Antiferromagnetism of the parent compounds strongly suggests that superconductivity and magnetism are closely related. However, the character of magnetic interactions and spin fluctuations in ferropnictides, in spite of vigorous efforts, has until now resisted understanding within any conventional model of magnetism. In this talk I will argue that the most puzzling features can be naturally reconciled within a rather simple effective spin model with biquadratic interactions, which is consistent with electronic structure calculations. By going beyond the Heisenberg model, this description explains numerous experimentally observed properties, including the peculiarities of the spin wave spectrum, thin domain walls, crossover from first to second order phase transition under doping in some compounds, and offers new insight in the occurrence of the nematic phase above the antiferromagnetic phase transition. These results will appear in February issues of Nature Physics and Physical Review.

If time permits I will show new results for recently discovered iron selenides.