Department of Chemistry, Graduate School of Science, Kyoto University, Japan.
Phys Rev Lett. 2011 Aug 5;107(6):066404. doi: 10.1103/PhysRevLett.107.066404. Epub 2011 Aug 4.
We addressed the so-far unresolved issue concerning the Co valence in the superconducting bilayer hydrated Na(x)CoO(2) · yH(2)O (x∼0.35, y∼1.3) using soft x-ray absorption spectroscopy at the Co-L(2,3) and O-K edges. We find that the valence state of the Co lies in a narrow range from +3.3 to +3.4 for all studied Na(x)CoO(2) · yH(2)O samples and their deuterated analogue with T(c)'s ranging from 3.8 to 4.7 K. These valence values are far from the often claimed +3.7, the number based on the Na content only. We propose to modify the phase diagram accordingly, where the basic electronic structure of the superconducting phase is very close to that of the Na(0.7)CoO(2) system, suggesting that the presence of in-plane spin fluctuations could play an important role for the superconductivity.
我们使用软 X 射线吸收光谱在 Co-L(2,3) 和 O-K 边缘解决了迄今为止关于超导双层水合 Na(x)CoO(2)·yH(2)O(x∼0.35,y∼1.3)中 Co 配位数的未解决问题。我们发现，对于所有研究的 Na(x)CoO(2)·yH(2)O 样品及其 T(c)范围为 3.8 到 4.7 K 的氘代类似物，Co 的价态在+3.3 到+3.4 的狭窄范围内。这些价态值远低于通常声称的+3.7，这个数值仅基于 Na 的含量。我们建议相应地修改相图，其中超导相的基本电子结构非常接近于 Na(0.7)CoO(2)系统，表明面内自旋涨落的存在可能对超导性起着重要作用。
