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Discovery of an Artificial Two Dimensional Superconductor with Graphene-like Structure
《物理评论快报》编辑推荐报道类石墨烯结构的人工二维超导体的发现

Recently, Prof. Jian Wang at Peking University, in collaboration with Prof. Qi-Kun Xue, Prof. Xu-Cun Ma, Prof. Xin-Cheng Xie, Prof. Xi Chen, Prof. Lin Gu, Prof. Hui Yang, Prof. Mingliang Tian, and Prof. Lian Li etc discovered a new 2D superconductor with graphene or silicone-like structure formed by the substrate. It is two-atom layer crystalline Ga grown on GaN(0001) by molecular beam epitaxy (MBE). Both in situ scanning tunneling spectroscopy and ex situ electrical magnetotransport and magnetization measurements show the superconductivity in such two-atom layer crystalline Ga. The superconducting transition temperature TC is 5.4 K, which is 5 times higher than TC in stable bulk Ga phase. The graphene-like structure, which is totally different with Ga bulk structure, might also induce some interesting properties in this two dimensional material. Besides, GaN substrate is a wide used semiconductor in industry, our result demonstrates a pathway for exploring atomic-scale 2D superconductors by surface and interface engineering in a broad range of metal-semiconductor heterostructures, which benefit from present semiconductor technology and ultrathin film fabrication technique. The results were published in Physical Review Letters (PRL 114, 107003(2015)) as an Editors’ Suggestion paper. Jian Wang and Xu-Cun Ma are corresponding authors of this paper. Huimin Zhang, Yi Sun and Wei Li contributed equally to this work.

 

The work was supported by National Basic Research Programs of China, National Natural Science Foundation of China, 1000 Talents Program for Young Scientists of China, the Research Fund for the Doctoral Program of Higher Education (RFDP) of China, and Collaborative Innovation Center of Quantum Matter, China.

 

Figure 1. Transmission electron microscopy (TEM) image of the interface of two-atom layer Ga on GaN substrate.

Figure 2. Transport result showing an onset Tc of 5.4 K. The inset is a schematic measurement structure.

    最近北大量子材料科学中心王健研究员与清华大学薛其坤院士、马旭村研究员、何珂、王立莉、季帅华、宋灿立等老师,以及北京大学谢心澄教授等人合作首次发现了一种新的二维超导相:两个原子层厚(0.556 nm)的晶体Ga生长在GaN(0001)表面上,形成宏观面积的类似石墨烯或硅烯的六角蜂巢结构,是新的一种人造二维晶格,其原子结构与原子间距与所有Ga的体相都不同。通过原位扫描隧道谱的探测以及非原位的电输运和磁化率测量,我们发现类石墨烯的Ga二维结构表现出约为5.4 K的超导转变温度,是Ga体材料稳定相Tc的五倍高,显示出界面增强的超导特性,是一种新的二维超导体。同时类石墨烯的二维蜂巢结构使得Ga薄膜可能具有其它重要特性。此外,这种新的二维极限下的单晶薄膜,超导转变温度Tc超过体材料稳定相,并可以通过覆盖保护层在大气环境下存活,对于常规超导体而言尚属首次。由于GaN为半导体工业中重要的光电材料(2014年诺奖),在其上制备的两原子层厚的超导薄膜就为超导电子学与半导体工艺的结合提供了可能。因此,GaN衬底上的类石墨烯结构的单晶Ga超导薄膜的发现,具有重要的物理意义及应用潜力。这一发现还得到中科院物理所谷林研究员、中科院苏州纳米所杨辉所长、中科院强场中心田明亮研究员以及美国威斯康辛大学Lian Li教授等人的鼎力协助。相关文章于2015310日在《物理评论快报》主页以编辑推荐的形式报道:Physical Review Letters 114, 107003(2015)。北大王健研究员与清华马旭村研究员为文章并列通讯作者。中科院物理所博士生张慧敏与北大孙祎博士、清华李渭博士为并列第一作者。(平均每六篇PRL文章会选出一篇作为编辑推荐文章)

上述研究得到国家重大科学研究计划、国家自然科学基金、中组部“青年千人”计划、高等学校博士学科点专项科研基金以及量子物质科学协同创新中心等项目经费的资助。

1:高分辨透射电镜图揭示两原子层的Ga生长在GaN(0001)表面上的原子排布。

2:电阻随温度的变化关系显示两原子层Ga薄膜的Tc5.4 K。插图为样品电输运测量示意图。