Dichotomy of superconductivity between monolayer FeS and FeSe-猫眼课题宝

DOI：

10.1073/pnas.1912836116

发表时间：

2019-11

期刊：

Proceedings of the National Academy of Sciences of the United States of America

影响因子：

11.1

通讯作者：

中科院分区：

综合性期刊1区

文献类型：

--

作者：

Koshin Shigekawa;K. Nakayama;M. Kuno;G. Phan;K. Owada;K. Sugawara;Takashi Takahashi;Takafumi Sato

在铁基超导体中，SrTiO 3上的单层FeSe显示出最高的超导转变温度（Tc），但起源仍然没有解决。虽然单层FeS具有与FeSe相同的晶体结构，但由于晶体生长困难及其亚稳态性质，因此不知道是否表现出超导性。我们采用拓扑反应和分子束外延方法成功地合成了单层硫化亚铁，并比较了两种方法的电子结构。而强烈的界面电子-声子耦合和电荷转移通过界面提出的来源，高Tc超导单层FeSe中也观察到在FeS中，高Tc超导是令人惊讶的缺席单层FeS。这种显着的差异为铁基超导体中高Tc超导性的机制提供了见解。高温（Tc）超导性在单层FeSe的SrTiO 3的发现提出了一个基本的问题：高Tc是否通常是在单层铁基超导体实现。由于块体FeS是一种超导体，其Tc可与同构FeSe的Tc相媲美，因此四硫化二铁是解决这一问题的关键材料。然而，由于其亚稳态性质，合成四元单层FeS的困难阻碍了进一步的研究。在这里，我们报告的单层硫化亚铁的能带结构的阐明，使在原位topotactic反应和分子束外延的独特组合。我们的角分辨光电子能谱上的FeS和FeSe揭示了显着的相似之处的电子结构，如重电子掺杂和界面的电子-声子耦合，这两者都被认为是可能的来源，高Tc的FeSe。然而，令人惊讶的是，高Tc超导性是不存在的单层FeS。这与电子掺杂多层FeS中的弱超导配对有关，其中界面效应不存在。我们的研究结果强烈表明，跨界面的电子-声子耦合增强Tc只有当它与超导层固有的配对相互作用。这一发现为探索异质界面高温超导体提供了关键的见解。

Significance Monolayer FeSe on SrTiO3 shows the highest superconducting-transition temperature (Tc) among iron-based superconductors, but the origin still remains unresolved. While monolayer FeS has the same crystal structure as FeSe, it is unknown to exhibit the superconductivity because of difficulty in crystal growth and its metastable nature. We have succeeded in synthesizing monolayer FeS by the topotactic reaction and molecular-beam epitaxy method, and compared the electronic structure between the 2. Whereas a strong interfacial electron–phonon coupling and a charge transfer through the interface proposed as a source for high-Tc superconductivity in monolayer FeSe are also observed in FeS, high-Tc superconductivity is surprisingly absent in monolayer FeS. Such striking difference provides insights into the mechanism of high-Tc superconductivity in iron-based superconductors. The discovery of high-temperature (Tc) superconductivity in monolayer FeSe on SrTiO3 raised a fundamental question: Whether high Tc is commonly realized in monolayer iron-based superconductors. Tetragonal FeS is a key material to resolve this issue because bulk FeS is a superconductor with Tc comparable to that of isostructural FeSe. However, difficulty in synthesizing tetragonal monolayer FeS due to its metastable nature has hindered further investigations. Here we report elucidation of band structure of monolayer FeS on SrTiO3, enabled by a unique combination of in situ topotactic reaction and molecular-beam epitaxy. Our angle-resolved photoemission spectroscopy on FeS and FeSe revealed marked similarities in the electronic structure, such as heavy electron doping and interfacial electron–phonon coupling, both of which have been regarded as possible sources of high Tc in FeSe. However, surprisingly, high-Tc superconductivity is absent in monolayer FeS. This is linked to the weak superconducting pairing in electron-doped multilayer FeS in which the interfacial effects are absent. Our results strongly suggest that the cross-interface electron–phonon coupling enhances Tc only when it cooperates with the pairing interaction inherent to the superconducting layer. This finding provides a key insight to explore heterointerface high-Tc superconductors.