Pnictogen height as a possible switch between high-Tc nodeless and low-Tc nodal pairings in the iron-based superconductors
Pnictogen height as a possible switch between high-Tc nodeless and low-Tc nodal pairings in the iron-based superconductors
复制标题
DOI：
10.1103/physrevb.79.224511
复制
发表时间：
2009-06-01
影响因子：
3.7
通讯作者：
Aoki, Hideo
中科院分区：
文献类型：
--
作者：
Kuroki, Kazuhiko;Usui, Hidetomo;Aoki, Hideo
我们采用几种LaFeAsO的虚拟晶格结构的五波段模型，以及从最大局域化万尼轨道得到的NdFeAsO和LaFePO等实际材料，研究了晶格结构对铁粒子自旋波动介导的超导性的影响。将随机相位近似应用于模型求解Eliashberg方程。这表明，间隙函数和超导不稳定性的强度是由费米表面不相连的碎片之间的多个嵌套产生的多个自旋涨落模式之间的合作或竞争决定的，而这些模式受晶格结构的影响。具体来说，在未展开布里温区（pi,pi）周围的费米表面伽马的出现对从Fe平面测量的光子原高度h（Pn）很敏感，其中h（Pn）显示为高t -c无节点和低t -c节点配对之间的开关。我们还发现，晶格常数的降低通常会抑制超导性。然后，我们可以将这些结合起来，得到一个关于pnicogen高度和晶格常数的通用超导相图。这表明与LaFeAsO相比，NdFeAsO有望表现出具有更高T-c的全间隙、符号反转的s波超导性，而LaFePO有望呈现出具有低T-c的节点配对，这与实验结果一致。
We study the effect of the lattice structure on the spin-fluctuation-mediated superconductivity in the iron pnictides adopting the five-band models of several virtual lattice structures of LaFeAsO, as well as actual materials such as NdFeAsO and LaFePO obtained from the maximally localized Wannier orbitals. Random phase approximation is applied to the models to solve the Eliashberg equation. This reveals that the gap function and the strength of the superconducting instability are determined by the cooperation or competition among multiple spin-fluctuation modes arising from several nestings among disconnected pieces of the Fermi surface, which is affected by the lattice structure. Specifically, the appearance of the Fermi surface gamma around (pi,pi) in the unfolded Brillouin zone is sensitive to the pnictogen height h(Pn) measured from the Fe plane, where h(Pn) is shown to act as a switch between high-T-c nodeless and low-T-c nodal pairings. We also find that reduction in the lattice constants generally suppresses superconductivity. We can then combine these to obtain a generic superconducting phase diagram against the pnictogen height and lattice constant. This suggests that NdFeAsO is expected to exhibit a fully gapped, sign-reversing s-wave superconductivity with a higher T-c than in LaFeAsO, while a nodal pairing with a low T-c is expected for LaFePO, which is consistent with experiments.