Reproduction of Experimental Gap Structure in LiFeAs based on the Orbital-Spin Fluctuation Theory: \(s_{++}\)-wave, \(s_\pm\)-wave, and hole-\(s_\pm\)-wave states

• Published in: arXiv.org 2014-06
• Main Authors: Saito, Tetsuro, Onari, Seiichiro, Yamakawa, Youichi, Kontani, Hiroshi, Borisenko, Sergey V, Zabolotnyy, Volodymyr B
• Format: Article
• Language: English
• Subjects: Fluctuation theory; Nesting; Superconductivity
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1402.2398

The absence of nesting between electron and hole-pockets in LiFeAs with \(T_c = 18\)K attracts great attention, as an important hint to understand the pairing mechanism of Fe-based superconductors. Here, we study the five-orbital model of LiFeAs based on the recently-developed orbital-spin fluctuation theories. It is found that the experimentally observed gap structure of LiFeAs, which is a "fingerprint" of the pairing mechanism, is quantitatively reproduced in terms of the orbital-fluctuation-mediated \(s_{++}\)-wave state. Especially, the largest gap observed on the small two hole-pockets composed of (\(d_{xz}, d_{yz}\)) orbitals can be explained, and this is a hallmark of the orbital-fluctuation-mediated superconductivity. The \(s_{++}\)-wave gap structure becomes more anisotropic in the presence of weak spin fluctuations. As the spin fluctuations increase, we obtain the "hole-\(s_\pm\)-wave state", in which only the gap of the large hole-pocket made of \(d_{xy}\)-orbital is sign-reversed, due to the cooperation of orbital and spin fluctuations. %out of the five pockets. This gap structure with "sign-reversal between hole-pockets" is similar to that recently reported in (Ba,K)Fe\(_2\)As\(_2\).