Evidence for superconducting gap nodes in the zone-centered hole bands of KFe2As2 from magnetic penetration-depth measurements
K. Hashimoto, A. Serafin, S. Tonegawa, R. Katsumata, R. Okazaki, T. Saito, H. Fukazawa, Y. Kohori, K. Kihou, C. H. Lee, A. Iyo, H. Eisaki, H. Ikeda, Y. Matsuda,… 展开作者
K. Hashimoto, A. Serafin, S. Tonegawa, R. Katsumata, R. Okazaki, T. Saito, H. Fukazawa, Y. Kohori, K. Kihou, C. H. Lee, A. Iyo, H. Eisaki, H. Ikeda, Y. Matsuda, A. Carrington, T. Shibauchi
备注：
6 pages, 6 figures, 1 table. Extended version to be published in Phys. Rev. B
在铁基磷属元素化物超导体中，KFe $_2$ As $_2$的特殊之处在于它的费米面不是由准嵌套的电子和空穴口袋组成。在这里，我们报告测量的温度依赖的伦敦渗透深度非常干净的晶体，这种化合物与剩余电阻率比$>1200$。我们发现，在低温下的超流密度表现出很强的线性温度依赖性，这意味着有线节点的能隙的大区域中心的孔片。结果表明，KFe $_2$ As $_2$是一种非常规的强电子关联超导体.
英文摘要：
Among the iron-based pnictide superconductors the material KFe$_2$As$_2$ is unusual in that its Fermi surface does not consist of quasi-nested electron and hole pockets. Here we report measurements of the temperature dependent London penetration depth of very clean crystals of this compound with residual resistivity ratio $>1200$. We show that the superfluid density at low temperatures exhibits a strong linear-in-temperature dependence which implies that there are line nodes in the energy gap on the large zone-centered hole sheets. The results indicate that KFe$_2$As$_2$ is an unconventional superconductor with strong electron correlations.
Observation of an isotropic superconducting gap at the Brillouin zone center of Tl$_{0.63}$K$_{0.37}$Fe$_{1.78}$Se$_2$
利用高分辨角分辨光电子能谱研究了超导体（SC）Tl $_{0.63}$ K $_{0.37}$ Fe $_{1.78}$ Se $_2$（$T_c=29$ K）在整个布里渊区（BZ）的结构.除了位于M $(π,0,0)$ -A $(π,0,π)$周围的准2D电子费米表面（FS）上的近各向同性$\sim$ 8.2 meV二维（2D）SC带隙（$2Δ/k_BT_c\sim7$）之外，我们还观察到Z中心电子FS上的$\sim 6.2$ meV各向同性SC带隙（$2Δ/k_BT_c\sim5$），该带隙排除了任何d波配对对称性，而是有利于s波对称性。所有各向同性SC间隙振幅可以通过来自局部强耦合方法的单个间隙函数拟合，这表明铁硫族化物超导体中的下一个相邻交换相互作用的增强。
Orbital-dependent electron correlation effect on the two- and three-dimensional Fermi surfaces in KFe2As2 revealed by angle-resolved photoemission spectroscopy
