Saint Petersburg State University , 198504 Saint Petersburg, Russia.
Donostia International Physics Center (DIPC) , 20018 San Sebastián/Donostia, Basque Country, Spain.
ACS Nano. 2017 Jan 24;11(1):368-374. doi: 10.1021/acsnano.6b05982. Epub 2017 Jan 6.
Graphene is one of the most promising materials for nanoelectronics owing to its unique Dirac cone-like dispersion of the electronic state and high mobility of the charge carriers. However, to facilitate the implementation of the graphene-based devices, an essential change of its electronic structure, a creation of the band gap should controllably be done. Brought about by two fundamentally different mechanisms, a sublattice symmetry breaking or an induced strong spin-orbit interaction, the band gap appearance can drive graphene into a narrow-gap semiconductor or a 2D topological insulator phase, respectively, with both cases being technologically relevant. The later case, characterized by a spin-orbit gap between the valence and conduction bands, can give rise to the spin-polarized topologically protected edge states. Here, we study the effect of the spin-orbit interaction enhancement in graphene placed in contact with a lead monolayer. By means of angle-resolved photoemission spectroscopy, we show that intercalation of the Pb interlayer between the graphene sheet and the Pt(111) surface leads to formation of a gap of ∼200 meV at the Dirac point of graphene. Spin-resolved measurements confirm the splitting to be of a spin-orbit nature, and the measured near-gap spin structure resembles that of the quantum spin Hall state in graphene, proposed by Kane and Mele [ Phys. Rev. Lett. 2005 , 95 , 226801 ]. With a bandstructure tuned in this way, graphene acquires a functionality going beyond its intrinsic properties and becomes more attractive for possible spintronic applications.
石墨烯由于其独特的类狄拉克锥形电子态分布和载流子的高迁移率，是纳米电子学中最有前途的材料之一。然而，为了促进基于石墨烯的器件的实现，必须对其电子结构进行必要的改变，可控地产生带隙。通过两种根本不同的机制，亚晶格对称性破缺或诱导强自旋轨道相互作用，可以分别将带隙的出现使石墨烯进入窄带隙半导体或二维拓扑绝缘体相，这两种情况在技术上都很相关。后一种情况，其特征在于价带和导带之间存在自旋轨道间隙，可以产生具有自旋极化的拓扑保护边缘态。在这里，我们研究了在与单层铅接触的情况下增强石墨烯的自旋轨道相互作用的效果。通过角分辨光发射谱，我们表明，在石墨烯片和 Pt(111)表面之间插入 Pb 夹层会导致在石墨烯的狄拉克点处形成约 200 meV 的间隙。自旋分辨测量证实了这种分裂是自旋轨道性质的，并且测量到的近隙自旋结构类似于 Kane 和 Mele 提出的石墨烯中的量子自旋霍尔态[Phys. Rev. Lett. 2005, 95, 226801]。通过这种方式调整能带结构，石墨烯获得了超越其固有特性的功能，并使其更适合于可能的自旋电子应用。
