Recently, the Shanghai Institute of Microsystem and Information Technology of the Chinese Academy of Sciences has achieved an important breakthrough in superconducting research. The state key laboratory of information functional materials, superconducting laboratory, Jiang Da, Hu Tao, etc., realized a graphene/ultra-thin superconducting Bi2Sr2CaCu2O8+x(Bi2212) heterojunction through mechanical peeling, in single cell cell and even half cell cell. Superconducting transitions above liquid nitrogen temperatures were found in thick Bi2212 materials.
The research paper High-Tc superconductivity in ultrathin Bi2Sr2CaCu2O8+x down to half-unit-cell thickness by protection with graphene was published on December 8th at Nature Communications (5:5708 doi: 10.1038/ncomms6708 (2014)).
Bi2212 is an important member of copper-based superconductors. Due to its strong anisotropy in copper-based superconducting materials, Bi2212 is one of the best systems for the study of quasi-2D superconductors. The international peers have used thin film deposition and single crystal etching methods to study the characteristics of ultra-thin Bi2212, but due to the limitations of material preparation and so on, whether the single-layer Bi2212 superconducting has been controversial.
In 2012, the team of graphene Nobel Prize winners used the mechanical stripping method to successfully prepare single-cell thick Bi2212 thin films. The material was found to be insulating. The Shanghai Institute of Microsystems superconducting team prepared graphene/ultra-thin Bi2212 heterojunction and found that Bi2212 with single and half-layer cell thickness exhibited superconductivity, and the transition temperature was higher than liquid nitrogen temperature. The study also found that the resistance temperature transition coefficient can accurately reflect the thickness information, and although the temperature coefficient of resistance and the surface resistance change in magnitude, the superconducting transition temperature does not change substantially.
The results suggest that the normal-state resistance transport properties of Bi222 materials may not be related to the superconducting mechanism. This finding has important reference significance for the further study of copper-based superconducting mechanism. The results also show that the graphene/ultra-thin Bi2212 heterojunction exhibits a distinct nonlinear IV characteristic, which provides a possibility for the development of new superconducting devices.
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