关于3d过渡金属化合物的非常规超导研究

The efforts that followed the discovery of the Fe-based superconductors in 2008, for which China played and is still playing a major role, has led us to reconsider the uniqueness of the cuprates. In order to push further our understanding of high-temperature superconductivity as a first step towards the engineering of novel superconductors with enhanced superconducting transition temperatures, the primary goal of the current proposal is to establish whether other superconductors, also based on 3d transition metals bridged by intermediate atoms, can be regarded as unconventional superconductors. With its capability to resolve the electronic structure of materials in the momentum space, Angle-Resolved Photoemission Spectroscopy (ARPES) is a powerful toll to characterize the electronic structure of materials directly in the momentum space. However, ARPES is mainly a surface sensitive technique, and it is often necessary to support ARPES data with other experimental techniques. By taking advantage of optical selection rules and the polarization flexibility of lasers, electronic Raman scattering allows one to measure superconducting gaps in the bulk of materials with some momentum information...Here we propose to combine Raman scattering and ARPES measurements to determine the electronic features common to all superconductors based on 3d transition metals. This new perspective where the Cu- and Fe-based superconductors are put side by side to the Ti-, Cr-, Co-, and Ni-based superconductors, is probably the only one that can unravel the keys for high-temperature superconductivity. We our convince that our results will stimulate and guide the search for new superconductors and that China should keep its role of International leader in this field.

自从2008年发现铁基超导体，人们重新审视铜基超导体的独特性，中国在这项研究中一直扮演着主要角色。寻找转变温度更高的新型超导体的第一步，就是深刻理解高温超导电性。此项目的首要目标就是研究由中间原子桥接的3d过渡金属组成的其它超导体是不是非常规超导体。角分辨光电子能谱（ARPES）具有动量空间分辨率，对于直接表征材料在动量空间的电子结构功能十分强大。但是由于ARPES是表面敏感的技术，它往往需要其他体相测量实验手段的支持。电子拉曼散射可以测量体材料中具有一定动量信息的超导能隙。..因此，我们在研究计划中提出，结合拉曼散射和ARPES测量手段来确定所有基于3d过渡金属超导体的电子性质。在新的视角下并排审视铜基、铁基超导体与钛、铬、钴、镍基超导体，这可能是揭示高温超导机制的唯一途径。我们相信我们的研究结果将激励和引导新超导体的发现。中国在这一领域应该继续保持国际领先地位。

非常规超导体研究是现代凝聚态物理领域的重要课题，对其深入了解可以带来电子器件的革命。3d过渡金属超导体令人感兴趣的电子性质在于它们的电子能带结构，特别是费米能级附近的电子态，这些电子态是非局域化的，因此迫切需要对其电子结构开展全面的研究。角分辨光电子能谱是一种能够直接获取费米面拓扑结构，超导能隙大小和对称性，以及动量空间分辨的能带结构的有力工具。然而，角分辨光电子能谱是一种表面敏感的分析技术，通常需要其他实验技术得到的结果作为参照。我们结合了角分辨光电子能谱和拉曼散射光谱两种技术来表征3d过渡金属超导体，着重表征超导能隙，超导能隙能直接反映配对机制。得益于拉曼光谱的光学选择定则和激光的偏振可调节性，我们可以获得带有部分动量信息的超导材料体相的超导能隙性质，从而为角分辨光电子能谱数据提供很好的佐证。.我们的主要成就是对在铁基超导材料122体系的向列序、超导态电子能隙，以及钛基、铬基超导体和一些新型拓扑材料的电子和晶体结构进行了研究。包括系统研究了K掺杂的BaFe2As2体系中的向列序涨落和超导能隙对称性，提出了不同的解释来阐明拉曼集合模式的产生机理；研究了LiTi2O4超导薄膜中的电声子耦合强度；研究了BaCr2As2体系中的能带重整化，并与同结构的铁基超导体作比较；对拓扑绝缘体KHgSb和外尔半金属NbAs的晶体结构及表面性质进行研究。我们获得的实验数据对进一步探讨和求证这些材料中的超导电子配对机制大有帮助。

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