Electrical Engineering Institute and Institute of Materials Science and Engineering, École Polytechnique Fédérale de Lausanne (EPFL) , Lausanne CH 1015, Switzerland.
Centre for Advanced 2D Materials, National University of Singapore , Singapore 117542, Singapore.
ACS Nano. 2017 Nov 28;11(11):11678-11686. doi: 10.1021/acsnano.7b06800. Epub 2017 Nov 1.
The observation of micrometer size spin relaxation makes graphene a promising material for applications in spintronics requiring long-distance spin communication. However, spin dependent scatterings at the contact/graphene interfaces affect the spin injection efficiencies and hence prevent the material from achieving its full potential. While this major issue could be eliminated by nondestructive direct optical spin injection schemes, graphene's intrinsically low spin-orbit coupling strength and optical absorption place an obstacle in their realization. We overcome this challenge by creating sharp artificial interfaces between graphene and WSe monolayers. Application of circularly polarized light activates the spin-polarized charge carriers in the WSe layer due to its spin-coupled valley-selective absorption. These carriers diffuse into the superjacent graphene layer, transport over a 3.5 μm distance, and are finally detected electrically using Co/h-BN contacts in a nonlocal geometry. Polarization-dependent measurements confirm the spin origin of the nonlocal signal. We also demonstrate that such signal is absent if graphene is contacted to bilayer WSe where the inversion symmetry is restored.
微米级自旋弛豫的观测使得石墨烯成为自旋电子学中需要远距离自旋通信的应用的有前途的材料。然而，接触/石墨烯界面处的自旋相关散射会影响自旋注入效率，从而阻止材料发挥其全部潜力。虽然通过无损的直接光学自旋注入方案可以消除这个主要问题，但石墨烯固有的低自旋轨道耦合强度和光吸收使其难以实现。我们通过在石墨烯和 WSe 单层之间创建锐利的人工界面来克服这一挑战。由于其自旋耦合的谷选择性吸收，圆偏振光会激活 WSe 层中的自旋极化载流子。这些载流子扩散到上覆的石墨烯层中，在 3.5μm 的距离上传输，最后通过 Co/h-BN 接触在非局域几何结构中进行电检测。偏振相关测量证实了非局域信号的自旋起源。我们还证明，如果石墨烯与双层 WSe 接触，其中反转对称性得到恢复，则不存在这种信号。
