Effects of Surface Electron Doping and Substrate on the Superconductivity of Epitaxial FeSe Films
Effects of Surface Electron Doping and Substrate on the Superconductivity of Epitaxial FeSe Films
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表面电子掺杂和衬底对外延 FeSe 薄膜超导性的影响
DOI：
10.1021/acs.nanolett.5b05243
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发表时间：
2016
期刊：
影响因子：
10.8
通讯作者：
Feng D. L.
中科院分区：
文献类型：
--
作者：
Zhang W. H.;Liu X.;Wen C. H. P.;Peng R.;Tan S. Y.;Xie B. P.;Zhang T.;Feng D. L.
在SrTiO 3衬底上生长的薄膜中，FeSe的超导电性大大增强，尽管其背后的机制仍不清楚。最近，表面钾（K）掺杂也被证明能够增强FeSe的超导电性。在这里，通过使用扫描隧道显微镜，我们比较了在两个衬底上生长的FeSe薄膜的超导电性的K掺杂的依赖性：SrTiO 3（001）和石墨化SiC（0001）。对于厚膜（20个单元电池（UC）），优化的超导（SC）的差距是类似的大小（109毫电子伏），无论基板。然而，当厚度减少到几个UC，优化SC间隙增加到15毫电子伏的SrTiO 3上的膜，而它保持不变的SiC上的膜。这清楚地表明，FeSe/SrTiO 3界面可以进一步增强超导电性，而不仅仅是掺杂电子。有趣的是，我们发现这种界面增强随着厚度的增加呈指数衰减，衰减长度为2.4 UC，这比晶格应变松弛的长度尺度短得多，指出界面电子-声子耦合是可能的起源。
Superconductivity in FeSe is greatly enhanced in films grown on SrTiO3substrates, although the mechanism behind remains unclear. Recently, surface potassium (K) doping has also proven able to enhance the superconductivity of FeSe. Here, by using scanning tunneling microscopy, we compare the K doping dependence of the superconductivity in FeSe films grown on two substrates: SrTiO3(001) and graphitized SiC (0001). For thick films (20 unit cells (UC)), the optimized superconducting (SC) gaps are of similar size (∼9 meV) regardless of the substrate. However, when the thickness is reduced to a few UC, the optimized SC gap is increased up to ∼15 meV for films on SrTiO3, whereas it remains unchanged for films on SiC. This clearly indicates that the FeSe/SrTiO3interface can further enhance the superconductivity, beyond merely doping electrons. Intriguingly, we found that this interface enhancement decays exponentially as the thickness increases, with a decay length of 2.4 UC, which is much shorter than the length scale for relaxation of the lattice strain, pointing to interfacial electron–phonon coupling as the likely origin.