PbBi_(3)低温合金薄膜的制备和超导性质  

Structural and superconducting properties of low-temperature ultrathin PbBi_(3) films

作　　者：王巨丰 田明阳 杜宏健 马传许 王兵 Wang Ju-Feng;Tian Ming-Yang;Du Hong-Jian;Ma Chuan-Xu;Wang Bing(Department of Physics,Hefei National Laboratory for Physical Sciences at the Microscale,University of Science and Technology of China,Hefei 230026,China)

机构地区：[1]中国科学技术大学合肥微尺度物质科学国家研究中心,物理系,合肥230026

出　　处：《物理学报》2022年第12期322-331,共10页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:12074359);中国科学院(批准号:XDB36020200)资助的课题。

摘　　要：铋(Bi)和铅(Pb)都是重元素,有很强的自旋-轨道耦合作用,由于原子半径接近,可形成丰富的原子取代合金结构.尽管对高温合金相有了较深入的研究,但对其低温物相的结构和超导物性的认识还很不全面.本文采用低温共沉积和低温退火的方法,在Si(111)-(7×7)衬底上制备了一种基于Bi(110)单晶结构中部分Bi原子被Pb取代的铅铋合金低温相超薄膜新结构,利用扫描隧道显微术(STM)对其结构和电子学性质进行了表征.通过结构表征,确定了合金薄膜表面呈现√2×√2R45°重构的PbBi_(3)合金相,其母体Bi(110)结构中25%的Bi原子被Pb取代了.通过STM谱学测量,发现合金相PbBi_(3)为超导相.变温实验表明,PbBi_(3)相的超导转变温度为6.13 K.在外加垂直磁场下出现的磁通涡旋结构表明PbBi_(3)薄膜是第Ⅱ类超导体,估算出上临界磁场的下限为0.92 T.测量了由Bi(110)-PbBi_(3)组成的共面型和台阶型正常金属-超导体异质结中的邻近效应,并研究了外加磁场对超导穿透深度影响.采用超导针尖与PbBi_(3)衬底形成超导-真空-超导隧道结,在超导能隙中观察到零偏压电导峰,进一步证实了PbBi_(3)的超导转变温度.Bismuth(Bi),as a stable heaviest element in the periodic table of elements,has strong spin-orbit coupling,which has attracted a lot of attention as the parent material of various known topological insulators.Previous calculations predicted that Bi(111)with a thickness less than eight bilayers and the ultrathin black-phosphoruslike Bi(110)films are single-element two-dimensional(2D)topological insulators.However,it is generally believed that these crystalline bismuth phases are not superconducting or their transition temperature should be lower than 0.5 mK.Lead(Pb)is a good superconducting elementary material,and there is a relatively small difference in radius between the Bi atom and Pb atom.According to the Hume-Rothery rule,it is expected that Pb/Bi alloys in an arbitrary ratio should be superconducting.One may thus expect to form crystalline Bi based superconductors by Pb substitution,which might host intriguing topological superconductivity.While our previous work has demonstrated a low-temperature stable Pb_(1-x)Bi_(x)(x~0.1)alloy phase in which Pb in the Pb(111)structure is partially replaced by Bi,the Bi crystalline structure-based phases of the superconducting alloys still lack in-depth research.Here,we report a new low-temperature phase of Pb-Bi alloy thin film,namely PbBi_(3),on the Si(111)-(7×7)substrate,by co-depositing Pb and Bi at a low temperature of about 100 K followed by an annealing treatment of 200 K for 2 h.Using low-temperature scanning tunneling microscopy and spectroscopy(STM/STS),we characterize in situ the surface structure and superconducting properties of the Pb-Bi alloy film with a nominal thickness of about 4.8 nm.Two spatially separated phases with quasitetragonal structure are observed in the surface of the Pb-Bi alloy film,which can be identified as the pure Bi(110)phase and the PbBi_(3)phase,respectively,based on their distinct atomic structures,step heights and STS spectra.The PbBi_(3)film has a base structure similar to Bi(110),where about 25% of the Bi atoms are replaced by P

关 键 词：铅铋合金 超导相干长度 邻近效应 零偏压电导峰 

分 类 号：O469[理学—凝聚态物理]