Fermi-surface-dependent superconducting gap in C6Ca
Fermi-surface-dependent superconducting gap in C6Ca
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DOI：
10.1038/nphys1128
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发表时间：
2009-01-01
期刊：
影响因子：
19.6
通讯作者：
Takahashi, T.
中科院分区：
文献类型：
--
作者：
Sugawara, K.;Sato, T.;Takahashi, T.
C_6Yb和C_6Ca超导电性的发现（参考文献1）引发了关于它是否在传统的Bardeen-Cooper-Schrieffer方案中描述或涉及其他奇异机制的激烈争论，因为超导转变温度（T-c）明显高于20世纪80年代被广泛研究的碱金属石墨层间化合物（参考文献2-4）。理解超导机制的关键在于与超导对形成相关的超导能隙。在这里，我们报告的第一个直接观察的超导间隙C6 Ca的高分辨率角分辨光电子能谱。我们发现在插入费米面上有1.8-2.0meV的超导能隙开放，而在石墨烯π能带的费米面上，差距很小或不存在。这些实验结果明确地表明，层间带在C6 Ca的高温超导性中起着至关重要的作用。
The discovery of superconductivity in C6Yb and C6Ca (ref. 1) has activated fierce debates on whether it is described within the conventional Bardeen-Cooper-Schrieffer scheme or some other exotic mechanisms are involved, because the superconducting transition temperature (T-c) is significantly higher than that of the alkali-metal graphite intercalation compounds intensively studied in the 1980s (refs 2-4). The key to understand the mechanism of superconductivity lies in the superconducting energy gap associated with the formation of superconducting pairs. Here, we report the first direct observation of a superconducting gap in C6Ca by high-resolution angle-resolved photoemission spectroscopy. We found that the superconducting gap of 1.8-2.0meV opens on the intercalant Fermi surface, whereas the gap is very small or absent on the Fermi surface derived from the pi* band of graphene layers. These experimental results unambiguously establish that the interlayer band has an essential role for the high-T-c superconductivity in C6Ca.