一种铅铋合金薄膜低温相的结构及超导物性表征  

Characterization of structure and superconducting properties of low-temperature phase of Pb-Bi alloy films

作　　者：田明阳 王巨丰 杜宏健 马传许 王兵[1] Tian Ming-Yang;Wang Ju-Feng;Du Hong-Jian;Ma Chuan-Xu;Wang Bing(Hefei National Laboratory for Physical Sciences at the Microscale,Department of Physics,University of Science and Technology of China,Hefei 230026,China)

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

出　　处：《物理学报》2021年第17期92-99,共8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：铅铋(Pb-Bi)合金超导材料被广泛研究,但对其低温物相的结构和超导物性却知之甚少.本文采用低温共沉积和低温退火的方法,在Si(111)-(7×7)衬底生长的Bi(111)超薄薄膜上制备了铅铋合金薄膜,利用扫描隧道显微术对其结构和电子学性质进行表征.通过结构表征,确定了薄膜中存在相分离,同时存在具有三次对称性的纯Bi(111)相和合金相Pb_(1-x)Bi_(x),可归属于部分铋取代的Pb(111)结构.通过电子学性质测量,进一步证实了Bi(111)相中特征的电子学结构及合金相中的超导行为.变温实验表明,合金相Pb_(1-x)Bi_(x)的超导转变温度是7.77 K,属于强耦合超导体.测量了由Bi(111)-Pb_(1-x)Bi_(x)组成的正常金属-超导体异质结和超导体-正常金属-超导体异质结中的邻近效应,指出了超导穿透深度可能受界面接触面积的影响.考虑到铋可能具有的拓扑属性,Bi(111)-Pb_(1-x)Bi_(x)面内异质结界面结构可进一步用于研究其新奇物理效应.Lead-bismuth(Pb-Bi)alloys,as a superconducting material,have been widely studied at their superconducting transition temperatures and the critical magnetic fields for different composition ratios.Most of experimental studies focused on the stable e phase formed at high temperatures,but less on the Pb-Bi alloys grown at low temperatures.So far,the structural and superconducting properties of the low-temperature Pb-Bi phases are far from good understanding.Here,we report our investigation of structural and superconducting properties of a low-temperature phase of Pb-Bi alloy.The Pb-Bi alloy films with a nominal thickness of about 6 nm are prepared by co-depositing Bi and Pb on Bi(111)/Si(111)-(7×7)substrates at a low temperature of 100 K followed by annealing at a treatment of 200 K for 2 h.The structural and superconducting properties of the Pb-Bi alloy films are characterized in situ by using low-temperature scanning tunneling microscopy/spectroscopy(STM/STS).It is observed that the spatially separated phases of nearly pure Bi(111)domains and Pb_(1-x)Bi_(x) alloy domains are formed in the films,where these phases can be identified by their distinct differences in the atomic structure and the distributions of step heights in the atomically resolved STM images,as well as by their distinguished STS spectra.The Pb_(1-x)Bi_(x) alloy phase presents the structure of Pb(111),in which about x≈0.1 Bi is substituted for Pb.The STS spectra show that the Pb_(1-x)Bi_(x) alloy phase is superconducting,with a transition temperature Tc=7.77 K derived from the variable-temperature measurements.This transition temperature is higher than that in pure Pb film(6.0-6.5 K),which can be well explained by the Mattias rules,with considering the fact that the average number of valance electrons increases after Bi atoms with five valance-electrons have been substituted for Pb atoms with four valance-electrons.The analysis shows that the ratio 2Δ(0)/k_(B)T_(C)is about 4.94 with the superconducting gapΔ(0)=1:66 meV at 0 K,indicating that t

关 键 词：铅铋合金 超导转变温度 邻近效应 扫描隧道显微术 

分 类 号：O511.3[一般工业技术—材料科学与工程]