State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, 865 Changning Road, Shanghai 200050, China.
Institute of Precision Optical Engineering, School of Physics Science and Engineering, Tongji University, Shanghai 200092, China.
Nat Commun. 2014 Dec 8;5:5708. doi: 10.1038/ncomms6708.
High-Tc superconductors confined to two dimension exhibit novel physical phenomena, such as superconductor-insulator transition. In the Bi2Sr2CaCu2O(8+x) (Bi2212) model system, despite extensive studies, the intrinsic superconducting properties at the thinness limit have been difficult to determine. Here, we report a method to fabricate high quality single-crystal Bi2212 films down to half-unit-cell thickness in the form of graphene/Bi2212 van der Waals heterostructure, in which sharp superconducting transitions are observed. The heterostructure also exhibits a nonlinear current-voltage characteristic due to the Dirac nature of the graphene band structure. More interestingly, although the critical temperature remains essentially the same with reduced thickness of Bi2212, the slope of the normal state T-linear resistivity varies by a factor of 4-5, and the sheet resistance increases by three orders of magnitude, indicating a surprising decoupling of the normal state resistance and superconductivity. The developed technique is versatile, applicable to investigate other two-dimensional (2D) superconducting materials.
限制在二维空间的高温超导体表现出新颖的物理现象，例如超导体-绝缘体转变。在 Bi2Sr2CaCu2O(8+x)（Bi2212）模型体系中，尽管已经进行了广泛的研究，但在薄膜极限下的固有超导性质仍难以确定。在这里，我们报告了一种方法，可以在石墨烯/Bi2212 范德华异质结构中制造高质量的单晶 Bi2212 薄膜，厚度低至半单位晶胞，在其中观察到尖锐的超导转变。由于石墨烯能带结构的狄拉克性质，该异质结构还表现出非线性电流-电压特性。更有趣的是，尽管临界温度在 Bi2212 的厚度减小的情况下基本保持不变，但正常态 T-线性电阻率的斜率变化了 4-5 倍，而面电阻增加了三个数量级，这表明正常态电阻和超导性的惊人解耦。所开发的技术具有通用性，可用于研究其他二维（2D）超导材料。
