Mou Daixiang, Kong Tai, Meier William R, Lochner Felix, Wang Lin-Lin, Lin Qisheng, Wu Yun, Bud'ko S L, Eremin Ilya, Johnson D D, Canfield P C, Kaminski Adam
Division of Materials Science and Engineering, Ames Laboratory, Ames, Iowa 50011, USA.
Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA.
Phys Rev Lett. 2016 Dec 30;117(27):277001. doi: 10.1103/PhysRevLett.117.277001. Epub 2016 Dec 28.
We use high resolution angle resolved photoemission spectroscopy and density functional theory with measured crystal structure parameters to study the electronic properties of CaKFe_{4}As_{4}. In contrast to the related CaFe_{2}As_{2} compounds, CaKFe_{4}As_{4} has a high T_{c} of 35 K at stochiometric composition. This presents a unique opportunity to study the properties of high temperature superconductivity in the iron arsenides in the absence of doping or substitution. The Fermi surface consists of several hole and electron pockets that have a range of diameters. We find that the values of the superconducting gap are nearly isotropic (within the explored portions of the Brillouin zone), but are significantly different for each of the Fermi surface (FS) sheets. Most importantly, we find that the momentum dependence of the gap magnitude plotted across the entire Brillouin zone displays a strong deviation from the simple cos(k_{x})cos(k_{y}) functional form of the gap function, proposed by the scenario of Cooper pairing driven by a short range antiferromagnetic exchange interaction. Instead, the maximum value of the gap is observed on FS sheets that are closest to the ideal nesting condition, in contrast to previous observations in other ferropnictides. These results provide strong support for the multiband character of superconductivity in CaKFe_{4}As_{4}, in which Cooper pairing forms on the electron and the hole bands interacting via a dominant interband repulsive interaction, enhanced by band nesting.
我们使用高分辨率角分辨光电子能谱以及结合实测晶体结构参数的密度泛函理论来研究CaKFe₄As₄的电子性质。与相关的CaFe₂As₂化合物不同，化学计量比组成的CaKFe₄As₄具有35K的高转变温度。这为在不进行掺杂或替代的情况下研究铁砷化物中的高温超导特性提供了独特的机会。费米面由几个具有不同直径的空穴和电子口袋组成。我们发现超导能隙的值几乎是各向同性的（在布里渊区的探测范围内），但对于每个费米面（FS）片层而言显著不同。最重要的是，我们发现在整个布里渊区绘制的能隙大小的动量依赖性与由短程反铁磁交换相互作用驱动的库珀对形成的情景所提出的简单cos(kₓ)cos(kᵧ)能隙函数形式有很大偏差。相反，与之前在其他铁基氮化物中的观察结果不同，可以在最接近理想嵌套条件的FS片层上观察到能隙的最大值。这些结果为CaKFe₄As₄中超导的多带特性提供了有力支持，其中库珀对在通过主导的带间排斥相互作用相互作用的电子和空穴带上形成，并因能带嵌套而增强。
