Wei Li, Jian Li, Jian-Xin Zhu, Yan Chen, C. S. Ting
We perform the first-principles band structure calculation on the iron-pnictide superconductor KFe$_2$As$_2$ and show that the Fe-$3d_{z^2}$ orbital character is quite strong around Z point. Based on this band structure, we propose an effective model, and examine all possible pairing symmetries for this compound. We find that the $k_z$-dependent s-wave pairing symmetry is most favored, if the interlayer pairing strength is comparable to the intralayer one. This pairing symmetry with nodes is originated from the large size of the hole pocket at the zone center and can be used to explain the neutron scattering experiments. However, the pairing symmetry appears to be $S_{x^2+y^2}$ like, if the magnetic exchange couplings obtained by first-principles calculation are used as pairing interactions.
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http://arxiv.org/abs/1203.2581
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