分子束外延硒化铁薄膜的超导电性  

Research on superconductivity of epitaxial Fe Se films

作　　者：宋灿立[1] 王立莉[1] 马旭村[1] 薛其坤[1] 

机构地区：[1]清华大学物理系,北京100084

出　　处：《科学通报》2015年第28期2739-2749,共11页Chinese Science Bulletin

基　　金：国家自然科学基金(11374336);国家重点基础研究发展计划(2015CB921001)资助

摘　　要：铁基超导体是继铜氧化合物高温超导体之后于2008年被发现的一类新型高温超导材料.在所有铁基超导体中,β-Fe Se因具有最简单的化学组分和结构而被认为是探索超导机制的理想体系.借助于半导体工业中成熟的分子束外延生长技术,研究者实现了对Fe Se超导薄膜生长、形貌和组分在原子水平上的精确控制,并在此基础上深入研究了其超导性质.最近研究者又把Fe Se薄膜的分子束外延生长拓展到Sr Ti O3(001)衬底,发现单层Fe Se/Sr Ti O3体系的超导转变温度有超过77 K的迹象.这些研究成果为解决高温超导体的配对机制以及进一步提高超导转变温度提供了全新的途径和思路,引起高温超导和材料科学等领域的广泛关注.The newly discovered iron-based superconductors in 2008 have become the second class of high temperature superconductor besides the cuprates. Among all these iron-based compounds, β-Fe Se has the simplest chemical structure and can be an archetype system for unraveling the mechanism of superconductivity. By using state-of-the-art molecular beam epitaxy（MBE） technique, high-quality superconducting Fe Se single crystalline films with finely controllable topography and composition have been successfully prepared, with their superconducting properties extensively investigated. The low-temperature scanning tunneling spectra reveal that the superconducting gap in the quasiparticle density of states is visible down to two unit cells of Fe Se films, and evidence for a gap function with nodal lines. Electron pairing with two-fold symmetry has also been demonstrated by direct imaging of quasiparticle excitations in the vicinity of magnetic vortex cores, Fe adatoms and Se vacancies. The two-fold pairing symmetry is supported by our observation of striped electronic nanostructures in the slightly Se-doped samples, primarily due to the orbital ordering. Twin boundaries run at approximately 45° to the Fe–Fe bond directions, and noticeably suppress the superconducting gap and pin magnetic vortices. This is likely caused by the increased Se height in the vicinity of twin boundaries, providing the first local evidence for the importance of this height to the mechanism of superconductivity. Furthermore, we reveal signatures of a bosonic mode in the local quasiparticle density of states of superconducting Fe Se films, whose energy reduces with decreasing gap magnitude ？. Recently, the growth recipe has been further extended to grow Fe Se film on Sr Ti O3（001） substrate, leading to the high-T c superconductivity in the very Fe Se/Sr Ti O3 interface. A superconducting gap as large as 20 me V and the magnetic field induced vortex state revealed by in situ scanning tunneling microscopy suggest that the superconductivity o

关 键 词：分子束外延 扫描隧道显微镜硒化铁 配对对称性 高温界面超导 

分 类 号：O511[理学—低温物理] O484[理学—物理]