我们表明，在石墨烯与小浓度的吸附原子，总的磁矩$μ_T$可以打开和关闭通过改变费米能量$E_F$，无论是通过施加栅极电压或通过适当的化学掺杂。我们的计算是使用一个简单的紧束缚模型，结合平均场处理的吸附原子上的电子-电子相互作用。通过石墨烯片和吸附原子之间的跳跃强度、吸附原子的原位能量和电子-电子相关能U的强度来控制开启或关闭时刻的$E_F$的值。我们的结果与Nair { \it et al.} [Nat.\ Commun. { \bf 4}，2010（2013）]。
英文摘要：
We show that, in graphene with a small concentration of adatoms, the total magnetic moment $μ_T$ can be switched on and off by varying the Fermi energy $E_F$, either by applying a gate voltage or by suitable chemical doping. Our calculation is carried out using a simple tight-binding model described previously, combined with a mean-field treatment of the electron-electron interaction on the adatom. The values of $E_F$ at which the moment is turned on or off are controlled by the strength of the hopping between the graphene sheet and the adatom, the on-site energy of the adatom, and the strength of the electron-electron correlation energy U. Our result is in qualitatively consistent with recent experiments by Nair {\it et al.} [Nat.\ Commun.\ {\bf 4}, 2010 (2013)].
The electronic transport of monolayer graphene devices is studied before and after \emph{in situ} deposition of a sub-monolayer coating of osmium adatoms. Unexpectedly, and unlike all other metallic adatoms studied to date, osmium adatoms shift the charge neutrality point to more positive gate voltages. This indicates that osmium adatoms act as electron acceptors and thus leave the graphene hole-doped. Analysis of transport data suggest that Os adatoms behave as charged impurity scatterers, albeit with a surprisingly low charge-doping efficiency. The charge neutrality point of graphene is foun…
Intervalley scattering of carriers in graphene at `top' adatoms may give rise to a hidden Kekulé ordering pattern in the adatom positions. This ordering is the result of a rapid modulation in the electron-mediated interaction between adatoms at the wavevector $K- K'$, which has been shown experimentally and theoretically to dominate their spatial distribution. Here we show that the adatom interaction is extremely sensitive to strain in the supporting graphene, which leads to a characteristic spatial modulation of the Kekulé order as a function of adatom distance. Our results suggest that the s…
The metal atoms, the alkali ones excepted, might provide the multiple outermost orbitals for the multi-orbital hybridizations with the out-of-plane $π$ bondings on the honeycomb lattice. This will dominate the fundamental properties of Al-, Ti- and Bi-adsorbed graphene nanoribbons, in which they are explored thoroughly by using the first-principles calculations. The principle focuses are the adatom-dependent binding energies, the adatom-carbon lengths, the optimal position, the maximum adatom concentrations, the free electron density transferred per adatom, the adatom-related valence and condu…
We have performed density functional theory calculations of graphene decorated with carbon adatoms, which bind at the bridge site of a C--C bond. Earlier studies have shown that the C adatoms have magnetic moments and have suggested the possibility of ferromagnetism with high Curie temperature. Here we propose to use a gate voltage to fine tune the magnetic moments from zero to 1$μ_B$ while changing the magnetic coupling from antiferromagnetism to ferromagnetism and again to antiferromagnetism. These results are rationalized within the Stoner and RKKY models. When the SCAN meta-GGA correction …
Early experiments on alkali-doped graphene demonstrated that the dopant adatoms modify the conductivity of graphene significantly, as extra carriers enhance conductivity while Coulomb scattering off the adatoms suppresses it. However, conductivity probes the overall scattering rate, so a dominant channel associated with long-range Coulomb scattering will mask weaker short-range channels. We present weak localization measurements of epitaxial graphene with lithium adatoms that separately quantify intra- and intervalley scattering rates, then compare the measurements to tight-binding calculation…
Fano-shaped impurity spectral density, electric-field-induced in-gap state and local magnetic moment of an adatom on trilayer graphene
最近，在石墨烯上的氢吸附原子中局部磁矩的存在已被实验证实[González-Herrero et al.，Science，2016，352，437]。受这一突破的启发，我们采用自洽平均场方法求解Anderson杂质模型，对三层石墨烯（TLG）上的顶位吸附原子进行了理论研究。详细考虑了堆积顺序、吸附位置和外加电场等因素的影响。我们发现，由于其独特的电子结构，TLG的情况是完全不同的单层石墨烯。首先，当杂质能级在费米能级附近时，菱面体堆叠TLG（r-TLG）上的吸附原子可以具有Fano形杂质谱密度，而不是正常的类洛伦兹谱密度。第二，外加电场可以将r-TLG上吸附原子的杂质能级调谐到隙内态，这强烈依赖于外加电场的方向，并且可以显著影响局部磁矩的形成。最后，我们系统地计算了杂质的磁相图，考虑了不同的堆垛级、吸附位置、掺杂和电场。研究表明，由于带隙态的存在，r-TLG的杂质磁相位也明显依赖于外加电场的方向。所有的理论结果都能在实验中得到验证，从而对TLG上吸附原子的局域磁矩有一个全面的认识。
We present a theoretical study of resonance characteristics in graphene from adatoms with $s$ or $p_z$ character binding in top, bridge, and hollow positions. The adatoms are described by two tight-binding parameters: onsite energy and hybridization strength. We explore a wide range of different magnitudes of these parameters by employing T-matrix calculations in the single adatom limit and by tight-binding supercell calculations for dilute adatom coverage. We calculate the density of states and the momentum relaxation rate and extract the resonance level and resonance width. Top position with…
We study the spectral function and quasiparticle scattering in Li-decorated graphene (Li@graphene) with an atomistic $T$-matrix formalism and uncover adatom-induced spectral effects which shed light on experimentally observed angle-resolved photoemission spectroscopy (ARPES) features. From transport studies, alkali adatoms are known to introduce charged-impurity scattering limiting the carrier mobility. Here, we demonstrate that Li adatoms furthermore give rise to a low-energy impurity band centered at the $Γ$ point which originates from the hybridization between the atomic 2s state of the Li …
The so-called spin-orbit proximity effect experimentally realized in graphene (G) on several different heavy metal surfaces opens a new perspective to engineer the spin-orbit coupling (SOC) for new generation spintronics devices. Here, via large-scale density functional theory (DFT) calculations performed for two distinct graphene/metal models, G/Pt(111) and G/Au/Ni(111), we show that the spin-orbit splitting of the Dirac cones (DCs) in these stuctures might be enhanced by either adsorption of adatoms on top of graphene (decoration) or between the graphene and the metal (intercalation). While …
A systematic study is made on geometric, electronic and magnetic properties of one-dimensional graphene nanoribbons using the first-principles calculations. The feature-rich essential properties result from the various orbital hybridizations in chemical bonds and the edge-carbon- and adatom-induced spin states. Pristine nanoribbons, with honeycomb lattices, can exhibit the planar, curving, scrolling, folding, and stacking configurations. Adatom adsorptions on surface and edge, respectively, create the buckled structures and the non-hexagonal/non-planar edges. There exist six kinds of of spin-d…
Hydrogen adatoms on graphene are investigated using DFT and analytical approaches. We demonstrate that the level of lattice deformation due to the hydrogen adsorption does not substantially change the coupling between the graphene $p_{z}$ orbitals. The hybridization primarily takes place between the adsorbate's s orbital and the graphene $p_{z}$ orbitals. We also show that the impurity interaction with the graphene atoms is limited to only a few nearest neighbors, allowing us to construct a compact TB model for the impurity-graphene system with an arbitrary impurity distribution. The complexit…
