论文标题
石墨烯在二维六角BN，ALN和GAN上：电子，自旋轨道和自旋松弛特性
Graphene on two-dimensional hexagonal BN, AlN, and GaN: Electronic, spin-orbit, and spin relaxation properties
论文作者
论文摘要
我们通过DFT计算研究了一系列2D六角氮化物绝缘子HXN，X = B，Al和GA上石墨烯的电子结构。基于对称的模型哈密顿量用于从接近二聚体石墨烯的低能量迪拉克带中提取轨道参数和旋转轨道耦合（SOC）。虽然相称的HBN诱导了大约10 MeV进入狄拉克频段的交错潜力，但较少的晶格匹配的Haln和Hgan的破坏了零点，却少了零点，而交错的间隙低于100美元$ $ $ EV。出乎意料的是，邻近的内在SOC不会超过原始石墨烯值12 $μ$ EV；它留在（1-16）$μ$ eV的窗口中，具体取决于堆叠。然而，当增加硼基组的原子数时，Rashba SoC急剧增加，计算出的最大值为8、15和65 $μ$ EV的B，AL和GA基氮化物。单个RASHBA耦合也很大程度上取决于堆叠，在对称旋转结构中消失，并且可以通过横向电场来调节。基于Chebyshev的扩展，将提取的自旋轨道参数用作自旋传输模拟的输入，从而对自旋期望值的时间进化进行了进化，从而为电子自旋松弛提供了有趣的预测。自旋寿命的幅度和各向异性在很大程度上取决于特定（HXN）/石墨烯/HXN系统，并且可以通过应用的外部电场以及石墨烯层中的载体密度有效调节它们。 A particularly interesting case for experiments is graphene/hGaN, in which the giant Rashba coupling is predicted to induce spin lifetimes of 1-10 ns, short enough to dominate over other mechanisms, and lead to the same spin relaxation anisotropy as observed in conventional semiconductor heterostructures: 50\%, meaning that out-of-plane spins relax twice as fast as in-plane spins.
We investigate the electronic structure of graphene on a series of 2D hexagonal nitride insulators hXN, X = B, Al, and Ga, with DFT calculations. A symmetry-based model Hamiltonian is employed to extract orbital parameters and spin-orbit coupling (SOC) from the low-energy Dirac bands of proximitized graphene. While commensurate hBN induces a staggered potential of about 10 meV into the Dirac bands, less lattice-matched hAlN and hGaN disrupt the Dirac point much less, giving a staggered gap below 100 $μ$eV. Proximitized intrinsic SOC surprisingly does not increase much above the pristine graphene value of 12 $μ$eV; it stays in the window of (1-16) $μ$eV, depending strongly on stacking. However, Rashba SOC increases sharply when increasing the atomic number of the boron group, with calculated maximal values of 8, 15, and 65 $μ$eV for B, Al, and Ga-based nitrides, respectively. The individual Rashba couplings also depend strongly on stacking, vanishing in symmetrically-sandwiched structures, and can be tuned by a transverse electric field. The extracted spin-orbit parameters were used as input for spin transport simulations based on Chebyshev expansion of the time-evolution of the spin expectation values, yielding interesting predictions for the electron spin relaxation. Spin lifetime magnitudes and anisotropies depend strongly on the specific (hXN)/graphene/hXN system, and they can be efficiently tuned by an applied external electric field as well as the carrier density in the graphene layer. A particularly interesting case for experiments is graphene/hGaN, in which the giant Rashba coupling is predicted to induce spin lifetimes of 1-10 ns, short enough to dominate over other mechanisms, and lead to the same spin relaxation anisotropy as observed in conventional semiconductor heterostructures: 50\%, meaning that out-of-plane spins relax twice as fast as in-plane spins.
