We study the effects of an attractive interaction between the boron (B) and the nitrogen (N) atoms doped in a bilayer graphene (BLG), BC$_{14}$N, on the electronic, the thermal and the optical properties for two different types of a doping process: First, both the B and the N atoms are doped in the same layer while the other layer is undoped. Second, the B and N atoms are doped in both layers. An attractive interaction between the B and N atoms does not influence the interlayer interaction in the first case, while it does in the second case. We find that the strong B-N attractive interaction in one layer induces metallic behavior due to the crossing of the valence band and the Fermi energy, while the strong attractive interaction between both layers induces a semiconductor property arising from the emergence a bandgap. We therefore confirm that the metallic-like BLG is not a good material for thermal devices because it has a low figure of merit, while we notice that the semiconductor-like BLG has a high Seebeck coefficient and figure of merit as well as a low thermal conductivity. The strong attractive interaction of the B-N atoms between the layers gives rise to a prominent peak to appear in dielectric function, the excitation and the absorption spectra in the low energy, visible range, while a very weak peak is seen in the case of a strong attractive interaction between the B and N doped in one layer. Controlling the B and N atomic configurations in the BLG may help to improve the material for use in both thermoelectric and optoelectronic devices.
We demonstrate that the electronic, thermal, and optical properties of a graphene bilayer with boron and nitrogen dopant atoms can be controlled by the interlayer distance between the layers in which the interaction energy and the van der Waals interaction between the dopant atoms play an essential role. We find a conversion of an AA- to an AB-stacked bilayer graphene caused by the repulsive interaction between dopant atoms. At a short interlayer distance, a strong repulsive interaction inducing a strong electric dipole moment of the dopant atoms is found. This gives rise to a breaking of the …
We study the effect of twisting on bilayer graphene. The effect of lattice relaxation is included; we look at the electronic structure, piezo-electric charges and spontaneous polarisation. We show that the electronic structure without lattice relaxation shows a set of extremely flat in-gap states similar to Landau-levels, where the spacing scales with twist angle. With lattice relaxation we still have flat bands, but now the spectrum becomes independent of twist angle for sufficiently small angles. We describe in detail the nature of the bands, and study appropriate continuum models, at the sa…
By using the first-principles method based on density of functional theory, we study the electronic properties of twisted bilayer graphene with some specific twist angles and interlayer spacings. With the decrease of the twist angle(the unit cell becomes larger), the energy band becomes narrower and Coulomb repulsion increases, leading to the enhancement of electronic correlation; On the other hand, as the interlayer spacing decreases and the interlayer coupling becomes stronger, the correlation becomes stronger. By tuning the interlayer coupling, we can realize the strongly correlated state w…
First principles calculation of structural and magnetic properties for Fe monolayers and bilayers on W(110)
采用全电子全势线性缀加平面波（FP-LAPW）方法，对5 ML W（110）衬底上的1和2个Fe单层（ML）结构进行了优化。最后，对优化后的结构进行了磁矩计算。我们发现Fe-W和相邻的Fe-Fe层间距与相应的体W-W和Fe-Fe层间距相比有显著的收缩（$\sim$ 10%）。与2.2 $μ_B$的Fe bcc体磁矩相比，Fe的表面层的磁矩增加了（i）对于1 ML Fe/5 ML W（110）增加了15%至2.54 $μ_B$，以及（ii）对于2 ML Fe/5 ML W（110）增加了29%至2.84 $μ_B$。2 ML Fe/5 ML W（110）的内层Fe层具有2.3 $μ_B$的类体磁矩。这些结果与以前的实验数据吻合得很好。
We theoretically investigate topological spin transport of the magnon-polarons in bilayer magnet with two-dimensional square lattices. Our theory is motivated by recent reports on the van der Waals magnets which show the reversible electrical switching of the interlayer magnetic order between antiferromagnetic and ferromagnetic orders. The magnetoelastic interaction opens band gaps and allows the interband transition between different excitation states. In the layered antiferromagnet, due to the interband transition between the magnon-polaron states, the spin Berry curvature which allows the t…
We present a multi-scale density functional theory (DFT) informed molecular dynamics and tight-binding (TB) approach to capture the interdependent atomic and electronic structures of twisted bilayer graphene. We calibrate the flat band magic angle to be at $θ_{\rm M} = 1.08^{\circ}$ by rescaling the interlayer tunneling for different atomic structure relaxation models as a way to resolve the indeterminacy of existing atomic and electronic structure models whose predicted magic angles vary widely between $0.9^\circ \sim 1.3^\circ$. The interatomic force fields are built using input from various…
Physical properties of two-dimensional van der Waals (vdWs) structures depend sensitively on both stacking orders and interlayer interactions. Yet, in most cases studied to date, the interlayer interaction is considered to be a static property of the vdWs structures. Here we demonstrate that applying a scanning tunneling microscopy (STM) tip pulse on twisted bilayer graphene (TBG) can induce sub-Angstrom fluctuations of the interlayer separation in the TBG, which are equivalent to dynamic vertical external pressure of about 10 GPa on the TBG. The sub-Angstrom fluctuations of the interlayer sep…
We explore a network of electronic quantum valley Hall (QVH) states in the moiré crystal of minimally twisted bilayer graphene. In our transport measurements we observe Fabry-Pérot and Aharanov-Bohm oscillations which are robust in magnetic fields ranging from 0 to 8T, in strong contrast to more conventional 2D systems where trajectories in the bulk are bent by the Lorentz force. This persistence in magnetic field and the linear spacing in density indicate that charge carriers in the bulk flow in topologically protected, one dimensional channels. With this work we demonstrate coherent electron…
We study ferromagnetism and its stability in twisted bilayer graphene. We work with a Hubbard-like interaction that corresponds to the screened Coulomb interaction in a well-defined limit where the Thomas-Fermi screening length $l_\text{TF}$ is much larger than monolayer graphene's lattice spacing $l_g \ll l_\text{TF}$ and much smaller than the Moiré super lattice's spacing $ l_\text{TF} \ll l_{\text{Moiré}}$. We show that in the perfectly flat band "chiral" limit and at filling fractions $\pm 3/4$, the saturated ferromagnetic (spin and valley polarized) states are ideal ground states candidat…
Large-angle twisted bilayer graphene (tBLG) is known to be electronically decoupled due to the spatial separation of the Dirac cones corresponding to individual graphene layers in the reciprocal space. The close spacing between the layers causes strong capacitive coupling, opening possibilities for applications in atomically thin devices. Here, we present a self-consistent quantum capacitance model for the electrostatics of decoupled graphene layers, and further generalize it to deal with decoupled tBLG at finite magnetic field and large-angle twisted double bilayer graphene at zero magnetic f…
We model bilayer graphene-like materials with Si$_2$C$_{14}$ and BC$_{14}$N stoichiometry, where the interlayer interactions play important roles shaping the physical properties of the systems. We find the interlayer interaction in Si$_2$C$_{14}$ to be repulsive due to the interaction of Si-Si atoms, and in BC$_{14}$N it is attractive due to B and N atoms for both the AA- and the AB-stacking. The repulsive interlayer interaction opens up a bandgap in Si$_2$C$_{14}$ while the attractive interlayer interaction in BC$_{14}$N induces a small indirect bandgap or overlaping of the valence conduction…
Photo- and thermally-induced huge layer decoupling in twisted bilayer WSe$_2$
RIKEN Center for Emergent Matter Science（RIKEN 新兴物质科学中心）；Quantum-Phase Electronics Center and Department of Applied Physics, The University of Tokyo（东京大学量子相电子中心及应用物理系）；Institute of Industrial Science, The University of Tokyo（东京大学工业科学研究所）；Research Center for Electronic and Optical Materials, National Institute for Materials Science（国立材料研究所电子与光学材料研究中心）；Research Center for Materials Nanoarchitectonics, National Institute for Materials Science（国立材料研究所材料纳米架构研究中心）
Controlling the phase behaviour of ultraconfined water via bilayer graphene stacking
University College London（伦敦大学学院）；Thomas Young Centre and London Centre for Nanotechnology（托马斯·杨中心与伦敦纳米技术研究中心）；Flatiron Institute（平顿研究所）；Columbia University（哥伦比亚大学）；University of Cambridge（剑桥大学）；Tohoku University（东北大学）；Yusuf Hamied Department of Chemistry, University of Cambridge（剑桥大学尤瑟夫·哈米德化学系）；Lennard-Jones Centre, University of Cambridge（剑桥大学伦纳德-琼斯中心）
