Spin relaxation in fluorinated single and bilayer graphene
Spin relaxation in fluorinated single and bilayer graphene
复制标题
DOI：
10.1103/physrevb.100.035421
复制
发表时间：
2019-03
影响因子：
3.7
通讯作者：
Susanne Wellnhofer;A. Stabile;D. Kochan;M. Gmitra;Ya-Wen Chuang;Jun Zhu;J. Fabian
中科院分区：
文献类型：
--
作者：
Susanne Wellnhofer;A. Stabile;D. Kochan;M. Gmitra;Ya-Wen Chuang;Jun Zhu;J. Fabian
我们提出了一个联合的实验和理论研究的作用，氟吸附原子的自旋和动量散射的电荷载流子在稀氟化石墨烯和双层石墨烯。实验自旋翻转和动量散射率和它们对氟和载流子掺杂的密度的依赖性，分别通过弱本地化和电导率测量，并建议氟作为共振磁性杂质的作用。对于几百ppm的估计氟浓度，观察到的自旋寿命在1-10 ps的范围内。理论上，我们通过拟合密度泛函超原胞计算建立了氟化石墨烯和双层石墨烯的紧束缚电子结构，并对相同器件内的自旋翻转和动量散射率进行了全面分析，旨在对两种散射通道进行一致的描述。我们发现，在石墨烯中的共振散射是非常敏感的共振能级的精确位置，以及巡回载体和本地化的自旋之间的交换耦合的大小。实验数据表明存在弱自旋翻转散射体，同时强烈地放松电子动量，几乎保持了电子-空穴对称性。这种散射体的共振能比密度泛函理论在稀释极限下预测的更接近中性点。列入氟吸附原子上的磁矩使我们能够定性地捕获的实验速率的载流子密度的依赖性，但预测更大（弱）的自旋（动量）弛豫率比测量。我们讨论可能的情况下，可能负责的差异。我们的系统研究揭示了准确捕捉石墨烯上吸附原子行为的复杂性。
We present a joint experiment-theory study on the role of fluorine adatoms in spin and momentum scattering of charge carriers in dilute fluorinated graphene and bilayer graphene. The experimental spin-flip and momentum scattering rates and their dependence on the density of fluorine and carrier doping are obtained through weak localization and conductivity measurements, respectively, and suggest the role of fluorine as resonant magnetic impurities. For the estimated fluorine concentration of a few hundred ppm, the observed spin lifetimes are in the range of 1–10 ps. Theoretically, we established tight-binding electronic structures of fluorinated graphene and bilayer graphene by fitting to density-functional supercell calculations and performed a comprehensive analysis of the spin-flip and momentum scattering rates within the same devices, aiming to develop a consistent description of both scattering channels. We find that resonant scattering in graphene is very sensitive to the precise position of the resonance level, as well as to the magnitude of the exchange coupling between itinerant carriers and localized spins. The experimental data point to the presence of weak spin-flip scatterers that, at the same time, relax the electron momentum strongly, nearly preserving the electron-hole symmetry. Such scatterers would exhibit resonance energies much closer to the neutrality point than what density-functional theory predicts in the dilute limit. The inclusion of a magnetic moment on fluorine adatoms allowed us to qualitatively capture the carrier-density dependence of the experimental rates but predicts a greater (weaker) spin (momentum) relaxation rate than the measurements. We discuss possible scenarios that may be responsible for the discrepancies. Our systematic study exposes the complexities involved in accurately capturing the behavior of adatoms on graphene.