多元FeSe基超导材料的结构与物性  

The crystal structure and physical properties of multiple components FeSe-based superconductors

作　　者：郭建刚[1] 陈小龙[1,2,3] 

机构地区：[1]中国科学院物理研究所,北京凝聚态物理国家实验室,北京100190 [2]中国科学院大学物理科学学院,北京100049 [3]量子物质科学协同创新中心,北京100190

出　　处：《科学通报》2017年第34期3967-3980,共14页Chinese Science Bulletin

基　　金：国家重点研发计划(2016YF0300600);国家自然科学基金重点项目(51532010);国家自然科学基金重大研究计划集成项目(91422303)资助

摘　　要：对FeSe基多元超导化合物的制备、晶体结构、相分离和超导性质等进行了详细的介绍.首先,利用碱金属插层的方法,制备出了三元K_xFe_(2–y)Se_2超导体,其超导转变温度为31 K,是当时FeSe基超导体的新纪录.同时,利用高温自助溶剂方法,制备出了K_xFe_(2–y)Se_2的晶体样品,并对其晶体结构、相分离和电子结构进行了细致的研究,从其特殊的费米面构型,可以看出K_xFe_(2–y)Se_2是区别于FeAs基超导体的新型高温超导体系.其次,通过低温液相法的制备手段,获得了多种碱金属插层FeSe的高温超导体,超导转变温度为30~46 K,大幅提高了FeSe基超导体的转变温度记录.在低温和中温区制备的FeSe基超导体中,存在极少量的Fe空位,可以精确标定超导相成分和电子结构,为研究FeSe基超导体甚至Fe基高温超导体的微观机理提供重要的实验证据.The sample preparation, crystallographic structure, phase separation and superconductivity of FeS e-based superconductors are discussed here. First of all, we will introduce the ternary high tempeature superconductor K（0.8）Fe（2-y）Se2 with superconducting transition tempeature（Tc） at 31 K, which creates the record Tc of FeSe-based superconductor under ambient pressure at that time. The single crystals can be grown through the self-flux method at high temperature. The crystal structure at high temperature shows the body-center tetragonal lattice with space group I4/mmm, while the superstructure developes at low tempeature with I4/m symmetry. The Fermi surface measured by angle resolution photoemission spectrum shows that K（0.8）Fe（2-y）Se2 has no any hole pockets at Fermi level, which is strikingly different from that of FeAs-based superconducors. This topology of Fermi surface implies that the superconducting mechanism of K（0.8）Fe（2-y）Se2 also should be distinguished from that of FeAs-based superconductors. The lack of interaction between electron and hole pockets would induce a possible d-wave superconducting gap. However, the mulitiple superstructure types, such as 5-（2/1） ×5-（2/1）, 2-（2/1） ×2-（2/1）, 2×2, etc, have been identified by transimission electron microscopy and neutron diffraction measurements, which reveal that K（0.8）Fe（2-y）Se2 is a phase-separated compound. Secondly, we develop the low tempeature liquid-NH3 method for synthesizing the pure FeSe-based superconducting compounds without phase separation. It is demonstrated that many alkali-metals, alkali-earth metals and rare-earth metals, such as Li, Na, Ca, Sr, Ba, Eu, and Yb, can be intercalated between FeSe layers and induce superconductivity with Tc of 30–46 K, which can further enhance the record Tc. In the Kx（NH3）yFe2Se2, two superconducting phases are discovered with different concentration of K（x≈0.3 and 0.6）. The NH3 molecures play an important role in stabilizing the structures,

关 键 词：FeSe基超导体 碱金属插层 晶体结构 电子结构 亚稳态合成方法 

分 类 号：O511.3[一般工业技术—材料科学与工程]