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Science Advances reports ICQM faculty member Wei Han group’s work on the inverse Edelstein effect in the Rashba-split 2DEG between SrTiO3 and LaAlO3 at room temperature
《Science Advances》刊登量子材料中心韩伟课题组关于全氧化物界面Rashba二维电子气中自旋和电荷转换的研究工作

Recently, Wei Han’s group, from the International Center for Quantum Materials (ICQM), demonstrated the spin injection and observation of inverse Edelstein effect in the Rashba-split 2DEG between SrTiO3 and LaAlO3 at room temperature. This work is cooperated with Jirong Sun’s group from institute of physics, Chinese academy of science. That is the first time to observe the inverse Edelstein effect generated spin signal in the 2DEG between two insulating oxides SrTiO3 and LaAlO3 up to room temperature. The work was reported by Science Advances with the title of “Observation of Inverse Edelstein Effect in Rashba-Split 2DEG between SrTiO3 and LaAlO3 at Room Temperature ”.

In 1990, Edelstein predicted that spin current could be induced by charge current flowing in inversion asymmetric two-dimensional electron gases (2DEGs), which is often referred to as the Edelstein effect (EE). The magnitude of EE highly depends on the Rashba spin-orbit coupling, which provides a locking between the momentum and spin polarization directions, as illustrated in fig (a). The opposite of EE is often called inverse Edelstein effect (IEE), which means that spin accumulation in inversion asymmetric 2DEG could generate an in-plane electric field perpendicular to the spin polarization direction. Because of the potential highly efficient spin-and-charge conversion, both the EE and IEE have attracted a great deal of interest for spintronics, and various experiments have been performed on the Rashba interfaces between two metallic films, two-dimensional materials, and the topological surface states.

Figure. Observation of inverse Edelstein effect (IEE) in Rashba-split 2DEG between SrTiO3 and LaAlO3 at room temperature. A, The energy dispersion for a typical Rashba spin-split 2DEG. B, Schematic drawing of the IEE measurements. C. The gate voltage dependence of IEE of the Rashba-split 2DEG between 3 UC LaAlO3 and SrTiO3 at room temperature. Credit: International Center for Quantum Materials, Peking University.

With the high-quality LAO/STO samples provided by the group of Jirong Sun, Wei Han’s group uses the spin pumping technique to inject the spin current from Py electrode through a LaAlO3 layer with a thickness of up to 40 unit cells into the 2DEG at the junction interface and measured the inverse Edelstein effect at the room temperature, as illustrated in the figure (b). Systematical measurements, including frequency, power, temperature and LAO thickness dependences of the spin signal strongly support the observation. As shown in figure(c), The gate voltage dependence of the spin signal indicate the gate voltage a powerful tool to turn the spin-to-charge conversion efficiency and even to turn the signal on/off.

This work has been published on Science Advances on March 17, 2017 (Science Advances, 3, e1602312 (2017)). PhD student Qi Song from ICQM and Hongrui Zhang from IOP are the co-first authors 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, the support by the 1000 Talents Program for Young Scientists of China.

Besides, it is worth to mention that the France team led by Prof. Fert, 2007 Nobel Laureate in physics, also did a work on the spin and charge conversion at the oxide interface. Their work is published in Nature Materials (Nature Materials 15, 1261–1266 (2016)), which is a little earlier than the work discussed above.

Both these two work reveal that the oxide interface could be used for spintronics devices, such as efficient charge-to-spin conversion for the generation and detection of spin current.

 

Links:

Link to the Science Advances paper:
http://advances.sciencemag.org/content/3/3/e1602312

Link to the Nature Materials paper by the France team led by Prof. Fert (2007 Nobel Laureate): http://www.nature.com/nmat/journal/v15/n12/full/nmat4726.html

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科院物理所孙继荣课题组共同合作,对Rashba自旋分裂的二维电子气进行了自旋注入和自旋电荷转换的研究,并在室温成功的发现逆Edelstein效应产生的自旋信号。该工作被《Science Advances》杂志以标题“Observation of Inverse Edelstein Effect in Rashba-Split 2DEG between SrTiO3 and LaAlO3 at Room Temperature”报道。

  早在上世纪90年代,Edelstein就预言在对称反演破缺的二维电子气中流动的电流会引起自旋流,这种现象被称为Edelstein效应。Edelstein效应的强弱取决于由反演对称性破缺导致的自旋轨道耦合。就像图(a)所示,这种自旋轨道耦合将载流子的动量方向和自旋方向锁定在一起。Edelstein效应的逆过程意味着在对称性破缺的二维电子气中不平衡的自旋注入和积聚可以产生面内电场,这种现象被称为逆Edelstein效应。由于Edelstein效应和逆Edelstein效应中潜在高效的自旋电流转换,近年来人们以Rashba界面、二维材料、拓扑表面态为载体进行了大量的实验。

  如图(b)所示,在孙继荣课题组提供的高质量SrTiO3/LaAlO3薄膜样品上,韩伟课题组使用自旋泵浦技术将自旋流从坡莫合金(Py)磁性电极穿过厚达40uc的LAO绝缘层注入到二维电子气中,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LAO厚度的变化关系,从各个方面证实了所观察到的信号。非常有趣的是,实验在室温下展现了门电压对自旋信号的调控作用,如图(c)所示。这意味着门电压可以被用作一个很强大的工具调节自旋电荷转化效率,甚至自旋信号的开关。

图: 在SrTiO3/LaAlO3异质结界面处Rashba二维电子气中观测到逆 Edelstein效应。A,Rashba自旋分裂的二维电子气的色散关系。B,逆 Edelstein效应测量示意图。C,室温下使用门电压调控SrTiO3/3UC LaAlO3界面处Rashba二维电子气中的逆Edelstein效应信号

  相关文章已于2017年03月17日在Science Advances上在线刊登(Science Advances, 3, e1602312 (2017))。北大博士生宋琪和物理所博士生张洪瑞为共同第一作者,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。

  另外,特别值得一提的是,诺贝尔奖得主法国Fert教授团队也对SrTiO3/LaAlO3界面的自旋和电荷转换进行了研究,他们的文章比韩伟课题组及其合作者的工作略早在Nature Materials上发表(Nature Materials 15, 1261–1266 (2016))。

  这两篇重要论文都揭示出复杂氧化物界面很有希望在未来被用以高效率的产生和探测自旋流,为基于复杂氧化物界面的新颖自旋器件奠定了基础。

  



论文链接: http://advances.sciencemag.org/content/3/3/e1602312

  



诺贝尔奖得主法国Fert教授团队的论文链接:



http://www.nature.com/nmat/journal/v15/n12/full/nmat4726.html

  



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