铁基超导体K_xFe_(2-y)Se_2的研究进展  

Research Progress of Iron-Based Superconductors K_xFe_(2-y)Se_2

作　　者：丁夏欣[1] 闻海虎[1] 

机构地区：[1]南京大学物理学院固体微结构国家重点实验室超导物理与材料研究中心,江苏南京210093

出　　处：《中国材料进展》2013年第9期513-521,561,共10页Materials China

基　　金：国家自然科学基金资助项目(A0402/11034011;A0402/11190023);科技部973计划项目(2011CBA00100;2012CB821403;2012CB21400)

摘　　要：自2008年在F掺杂的LaOFeAs化合物中发现高达26 K的超导电性后,高温超导研究迎来了新一轮热潮。随后一系列不同结构的铁基超导材料被发现,到目前为止,铁基超导体的最高临界温度记录为56 K。在2010年末,临界温度高达32 K的KxFe2-ySe2这一新的铁硫族超导体被发现。与其他铁磷族超导体相比,这个系统有着许多不同寻常的性质。角分辨光电子谱实验与能带结构计算都表明此材料在费米能附近没有空穴型费米面。这一性质强烈地挑战了被广为接受的S±超导配对图像:理论物理学家提出在铁基超导体中,电子在空穴型费米面与电子型费米面之间散射,通过交换反铁磁自旋涨落来达到超导配对。不久之后,在此材料中又确定了相分离的性质。其中一个主要的相是具有K2Fe4Se5结构的反铁磁绝缘相,另一个是少量的超导相。闻海虎小组最近的一篇论文认定了此材料的超导相以三维网络状的细丝形态存在,相关实验数据表明每8个Fe原子位置中存在1个空位,并由此提出超导的母体相是由Fe空位形成的槡槡8×10这种有序平行四边形结构组成。文章比较全面地介绍这一快速发展领域的研究进展,包括晶体生长与淬火处理,Fe空位有序与块反铁磁相,相分离与超导相的探索,配对对称性与能隙结构。最后列举了一些重要的问题,并且展望了将来的研究内容。Since the discovery in 2008 of superconductivity at 26 K in fluorine-doped LaFeAsO, the research has been tuned to a new direction on high temperature superconductivity. So far, several types of iron-based superconductors with different structures have been discovered, with the highest transition temperature to date being 56 K. By the end of 2010, the iron-chalcogenide superconductor KxFe2-ySe2 with Tc - 32 K was discovered. This system shows a set of distinctive properties as compared with other iron-pnictide compounds. Both angle resolved photoemission spectroscopy experiments and band structure calculations indicate that the hole pockets are missing at the Fermi energy. This greatly challenges the widely perceived picture that the superconducting pairing is established by exchanging antiferromagnetic （AF） spin fluctu- ations and the electrons are scattered between the electron and hole pockets. Later, it was found that this material sepa- rates into two phases-a dominant AF insulating phase with a K2 Fe4 Se5 structure, and a minority superconducting phase. A recent paper of Hai-Hu Wen＇ s group identifies a three-dimensional network of superconducting filaments within this mate- rial and present evidence for the existence of K2 Fe7 Ses which may be the possible parent phase for superconductivity. This 278 phase has a Fe structure of a single Fe vacancy out of every eight Fe-sites arranged in a √8×√10 parallelogram struc- ture. The status of research in this rapidly growing field is reviewed which includes crystal growth and quenching tech- nique, Fe-vacancy orders and the block-AF state, phase separation and the hunt for the superconducting phase, pairing symmetry and the gap structure. In the end, important issues are listed as perspective for future research.

关 键 词：铁基超导 高温超导体 相分离 超导母体 KxFe2-ySe2 

分 类 号：TH142.8[一般工业技术—材料科学与工程]