论文标题
电场和底物在石墨烯中急剧加速自旋松弛
Electric fields and substrates dramatically accelerate spin relaxation in graphene
论文作者
论文摘要
从理论上讲，石墨烯中的电子保留旋转状态的时间比大多数材料长得多，这使石墨烯成为旋转和量子信息技术的有前途的平台。在这里，我们使用第一原理密度 - 矩阵（FPDM）动力学模拟，以表明与电场和底物的相互作用可通过与声子散射强烈增强自旋松弛。因此，室温下的松弛时间从六角形硝酸硼（HBN）底物上的石墨烯中的微秒降低到石墨烯的纳米秒，这是实验中通常测量的数量级。此外，与传统的D'Yakonov-perel'（DP）模型预测，HBN的反转对称性破裂引入了电子和孔自旋寿命更强的不对称性。与常规DP模型的偏差对于平面自旋松弛更强，导致平面外至平面内寿命比大于1/2，最大接近DIRAC点。这些FPDM结果与特定于对称性的假设或材料依赖性参数无关，还验证了DP模型的最新修改以解释此类偏差。总体而言，我们的结果表明，在底物存在下的自旋 - 音波松弛可能比通常假设更重要，需要在室温下考虑基于石墨烯的自旋技术。
Electrons in graphene are theoretically expected to retain spin states much longer than most materials, making graphene a promising platform for spintronics and quantum information technologies. Here, we use first-principles density-matrix (FPDM) dynamics simulations to show that interaction with electric fields and substrates strongly enhance spin relaxation through scattering with phonons. Consequently, the relaxation time at room temperature reduces from microseconds in free-standing graphene to nanoseconds in graphene on hexagonal boron nitride (hBN) substrate, the order of magnitude typically measured in experiments. Further, inversion symmetry breaking by hBN introduces a stronger asymmetry in electron and hole spin lifetimes, than predicted by the conventional D'yakonov-Perel' (DP) model for spin relaxation. Deviations from the conventional DP model are stronger for in-plane spin relaxation, resulting in out-of-plane to in-plane lifetime ratios much greater than 1/2 with a maximum close to the Dirac point. These FPDM results, independent of symmetry-specific assumptions or material-dependent parameters, also validate recent modifications of the DP model to explain such deviations. Overall, our results indicate that spin-phonon relaxation in the presence of substrates may be more important in graphene than typically assumed, requiring consideration for graphene-based spin technologies at room temperature.
