Laboratory of Atomic and Solid State Physics, Department of Physics, Cornell University, Ithaca, NY 14853, USA.
Science. 2010 Jan 8;327(5962):181-4. doi: 10.1126/science.1181083.
The mechanism of high-temperature superconductivity in the newly discovered iron-based superconductors is unresolved. We use spectroscopic imaging-scanning tunneling microscopy to study the electronic structure of a representative compound CaFe1.94Co0.06As2 in the "parent" state from which this superconductivity emerges. Static, unidirectional electronic nanostructures of dimension eight times the inter-iron-atom distance a(Fe-Fe) and aligned along the crystal a axis are observed. In contrast, the delocalized electronic states detectable by quasiparticle interference imaging are dispersive along the b axis only and are consistent with a nematic alpha2 band with an apparent band folding having wave vector q vector congruent with +/-2pi/8a(Fe-Fe) along the a axis. All these effects rotate through 90 degrees at orthorhombic twin boundaries, indicating that they are bulk properties. As none of these phenomena are expected merely due to crystal symmetry, underdoped ferropnictides may exhibit a more complex electronic nematic state than originally expected.
在新发现的铁基超导体中，高温超导的机制尚未解决。我们使用光谱成像-扫描隧道显微镜研究了在这种超导出现的母体状态下具有代表性的化合物 CaFe1.94Co0.06As2 的电子结构。观察到尺寸为铁-铁原子距离 a(Fe-Fe)的八倍且沿晶体 a 轴排列的静态、单向电子纳米结构。相比之下，准粒子干涉成像可探测到的非局域电子态仅沿 b 轴色散，与具有明显带折叠的向列 alpha2 带一致，在 a 轴上沿 q 矢量与 +/-2pi/8a(Fe-Fe)一致。所有这些效应在正交孪晶边界处旋转 90 度，表明它们是体相性质。由于这些现象都不仅仅是由于晶体对称性引起的，因此欠掺杂的亚铁砷化物可能表现出比最初预期更复杂的电子向列态。
