Superconductivity across Lifshitz transition and anomalous insulating state in surface K-dosed (Li0.8Fe0.2OH)FeSe
Superconductivity across Lifshitz transition and anomalous insulating state in surface K-dosed (Li0.8Fe0.2OH)FeSe
复制标题
Lifshitz转变的超导性和表面掺钾(Li0.8Fe0.2OH)FeSe中的反常绝缘态
DOI：
10.1126/sciadv.1603238
复制
发表时间：
2017-07-01
期刊：
影响因子：
13.6
通讯作者：
Feng, Dong-Lai
中科院分区：
文献类型：
--
作者：
Ren, Mingqiang;Yan, Yajun;Feng, Dong-Lai
在铁基超导体中，理解掺杂后的超导电性与电子结构之间的关系对于探索配对机制至关重要。最近，人们发现，在硒化铁（FeSe），增强的超导电性（超过40 K的Tc）可以通过电子掺杂实现，费米面只包括M中心的电子口袋。利用表面K掺杂、扫描隧道显微镜/光谱和角分辨光电子能谱，研究了（Li0.8Fe0.2OH）FeSe深电子掺杂体系的电子结构和超导电性.我们发现，一个以伽马为中心的电子带，它最初位于费米能级（E-F）之上，可以不断地被调谐到跨越EF，并在伽马处贡献一个新的电子袋。当这种Lifshitz转变发生时，在M-中心的电子口袋中的超导性被稍微抑制，并且在新的伽马电子口袋上观察到具有小尺寸（高达类似于5 meV）和圆顶状掺杂依赖性的可能的超导间隙。在进一步的K剂量下，系统最终演变成绝缘状态。我们的研究结果提供了新的线索，以了解超导性与费米表面拓扑结构和相关效应的FeSe基超导体。
In iron-based superconductors, understanding the relation between superconductivity and electronic structure upon doping is crucial for exploring the pairing mechanism. Recently, it was found that, in iron selenide (FeSe), enhanced superconductivity (T-c of more than 40 K) can be achieved via electron doping, with the Fermi surface only comprising M-centered electron pockets. By using surface K dosing, scanning tunneling microscopy/spectroscopy, and angle-resolved photoemission spectroscopy, we studied the electronic structure and superconductivity of (Li0.8Fe0.2OH)FeSe in the deep electron-doped regime. We find that a Gamma-centered electron band, which originally lies above the Fermi level (E-F), can be continuously tuned to cross EF and contribute a new electron pocket at Gamma. When this Lifshitz transition occurs, the superconductivity in the M-centered electron pocket is slightly suppressed, and a possible superconducting gap with a small size (up to similar to 5 meV) and a dome-like doping dependence is observed on the new Gamma electron pocket. Upon further K dosing, the system eventually evolves into an insulating state. Our findings provide new clues to understand superconductivity versus Fermi surface topology and the correlation effect in FeSe-based superconductors.