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Nature Communications reports ICQM faculty member Wei Han group’s work on spin to charge conversion of the topological surface states of SmB6
《自然通讯》刊登量子材料中心韩伟课题组关于拓扑表面态中自旋性质的研究工作

Recently, Prof. Wei Han’s group, from the International Center for Quantum Materials (ICQM), demonstrated the spin injection and observation of inverse Edelstein effect in the surface state of a topological Kondo insulator (TKI), SmB6. This work is cooperated with Jing Shi’s group, Chi Zhang’s group from ICQM, Tao Wu’s group and Xian Hui Chen’s group from University of Science and Technology of China. That’s the first time to observe the inverse Edelstein effect generated spin signal in pure surface states of topological insulators, by excluding the contributions from the bulk states. The work was reported by Nature Communications with the title of “Spin injection and inverse Edelstein effect in the surface states of topological Kondo insulator SmB6”.

Spintronics aims to use the spin degrees of freedom for information storage and computing technologies. Topological insulators, a class of quantum materials, have special gapless surface states, where the spin polarization of the Dirac fermions is locked to the momentum direction as illustrated in the figure (a). This spin-momentum locking property gives rise to very interesting spin-dependent physical phenomena such as the Edelstein and inverse Edelstein effects. However, a major obstacle to the clean demonstration of the Edelstein/inverse Edelstein effects for the spin–momentum locked surface states is the presence of unavoidable bulk carriers which dominate the conduction in these Bi2Se3-based three-dimensional TI. Recently, SmB6, a Kondo insulator, has been found to be a new type of TI. At temperatures below 3K, the bulk states are insulating, and only surface carriers contribute to the conduction, as demonstrated in figure (b) and the previous surface Hall measurements from other groups. 

With the SmB6 samples provided by the group of Tao Wu and Xian Hui Chen and low temperature microwave techniques in the He-3 refrigerator provided by Jian Mi and Chi Zhang, Wei Han’s group use the spin pumping technique to inject the spin current from Py to SmB6 and measured the inverse Edelstein effect as illustrated in the figure (c) and (d). Systematical measurements, including frequency, power, temperature and the magnetic field angle dependences of the spin signal strongly support the observation. This observation could lead to future studies of the role of strong correlation in TKIs for spintronics and highly efficient spin current generation in the surface states of TIs via the materials design and engineering.

This work has been published online in Nature communications on Nov. 11th, 2016(Nature Communications, 7, 13485 (2016); doi: 10.1038/ncomms13485. ICQM PhD student Qi Song is the first author of this paper. This work was supported by National Basic Research Programs of China, National Natural Science Foundation of China, the Strategic Priority Research Program of the Chinese Academy of Sciences, Recruitment Program of Global Experts, CAS Hundred Talent Program, the DOE BES Award, and the support by the 1000 Talents Program for Young Scientists of China.

Links:
Link to the paper: http://www.nature.com/articles/ncomms13485
Link to Prof. Wei Han’s group page: http://www.phy.pku.edu.cn/~LabSpin/home.html
 

  近日, 北京大学量子材料科学中心韩伟课题组与中心施靖课题组、张弛课题组、谢心澄课题组、中国科学技术大学的陈仙辉、吴涛课题组共同合作,对近藤拓扑绝缘体SmB6的表面态进行了自旋注入的实验,并成功发现了拓扑表面态中的逆Edelstein效应。这是人们首次成功地排除了拓扑绝缘体体态的干扰,更为纯净地展示来自拓扑绝缘体表面态的逆Edelstein效应。该工作被《自然通信》杂志以标题“Spin injection and inverse Edelstein effect in the surface states of topological Kondo insulator SmB6”报道。

  自旋电子学一直致力于利用自旋自由度来研发新型的信息存储和信息技术。拓扑绝缘体作为一种新型的量子物质,在其表面态上狄拉克费米子的自旋极化方向和其动量方向是锁定在一起的,如图(a)所示。这种自旋轨道锁定会引起一些非常有趣的自旋相关的现象,比如Edelstein效应和逆Edelstein效应。但是当人们以基于Be2Se3 的三维拓扑绝缘体为载体去展示这种来自表面态的自旋轨道锁定的性质时,体态自旋轨道耦合效应的存在成为了一个很难排除的干扰。近几年研究发现SmB6是一种新型的近藤拓扑绝缘体。正如图(b)所示,当温度低于~3K时,SmB6的体态将变得绝缘,只有表面态的载流子对导电有贡献。因此,近藤拓扑绝缘体是一种更为理想的研究拓扑绝缘体表面态性质的载体。

  如图(c)和图(d)所示,在陈仙辉课题组提供的SmB6样品和张弛课题组提供的微波氦3低温环境的帮助下,韩伟课题组使用自旋泵浦技术从坡莫合金(Py)向SmB6 注入自旋流,并进行逆Edelstein效应的测量。工作系统地测量了逆Edelstein效应随频率、功率、温度和磁场角度的变化关系,从各个方面证实了所观察到的信号。在新型近藤拓扑绝缘体SmB6的表面态中对逆Edelstein效应的发现,将会进一步推动关于近藤拓扑绝缘体中的强关联物理的研究,并进一步推进人们在拓扑绝缘体表面态中探索如何更高效率地产生自旋流的步伐。

  此文章已于2016年11月11日在《自然通信》上在线刊登(Nature Communications, 7, 13485 (2016); doi: 10.1038/ncomms13485),北大博士生宋琪为第一作者,该项工作得到了国家自然科学基金委、国家科技部、中科院、中科院百人计划以及中组部千人计划的经费支持。

 

  链接:



  论文链接: http://www.nature.com/articles/ncomms13485



  韩伟研究员实验室主页: http://www.phy.pku.edu.cn/~LabSpin/home.html