Solid State Chemistry, Max Planck Institute for Chemical Physics of Solids, D-01187 Dresden, Germany.
New Technologies Research Centre, University of West Bohemia, 306 14 Pilsen, Czech Republic.
Proc Natl Acad Sci U S A. 2017 Nov 21;114(47):12425-12429. doi: 10.1073/pnas.1702234114. Epub 2017 Nov 6.
The superconducting phase in iron-based high-[Formula: see text] superconductors (FeSC), as in other unconventional superconductors such as the cuprates, neighbors a magnetically ordered one in the phase diagram. This proximity hints at the importance of electron correlation effects in these materials, and Hund's exchange interaction has been suggested to be the dominant correlation effect in FeSCs because of their multiband nature. By this reasoning, correlation should be strongest for materials closest to a half-filled [Formula: see text] electron shell (Mn compounds, hole-doped FeSCs) and decrease for systems with both higher (electron-doped FeSCs) and lower (Cr-pnictides) [Formula: see text] counts. Here we address the strength of correlation effects in nonsuperconducting antiferromagnetic BaCrAs by means of angle-resolved photoemission spectroscopy (ARPES) and first-principles calculations. This combination provides us with two handles on the strength of correlation: First, a comparison of the experimental and calculated effective masses yields the correlation-induced mass renormalization. In addition, the lifetime broadening of the experimentally observed dispersions provides another measure of the correlation strength. Both approaches reveal a reduction of electron correlation in BaCrAs with respect to systems with a [Formula: see text] count closer to five. Our results thereby support the theoretical predictions that Hund's exchange interaction is important in these materials.
铁基高温超导（FeSC）中的超导相，与铜酸盐等其他非常规超导体一样，在相图中与磁有序相相邻。这种接近表明电子相关效应在这些材料中的重要性，由于其多带性质，Hund 交换相互作用被认为是 FeSCs 中的主要相关效应。根据这一推理，对于最接近半满[Formula: see text]电子壳层的材料（Mn 化合物、空穴掺杂的 FeSCs），相关性应该最强，而对于具有更高（电子掺杂的 FeSCs）和更低（Cr-磷化物）[Formula: see text]数的系统，相关性应该减弱。在这里，我们通过角分辨光电子能谱（ARPES）和第一性原理计算来研究非超导反铁磁 BaCrAs 中的相关效应强度。这种组合为我们提供了两种衡量相关强度的方法：首先，通过比较实验和计算得出的有效质量，得出了关联引起的质量重整化。此外，实验观察到的色散的寿命展宽提供了另一种衡量关联强度的方法。这两种方法都表明，与[Formula: see text]计数更接近五的系统相比，BaCrAs 中的电子关联有所减弱。我们的结果支持了理论预测，即 Hund 交换相互作用在这些材料中很重要。
