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Register a new userRashba interaction and local magnetic moments in a graphene-Boron Nitride heterostructure by intercalation with Au
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We intercalate a van der Waals heterostructure of graphene and hexagonal Boron Nitride with Au, by encapsulation, and show that Au at the interface is two dimensional. A charge transfer upon current annealing indicates redistribution of Au and induces splitting of the graphene bandstructure. The effect of in plane magnetic field confirms that splitting is due to spin-splitting and that spin polarization is in the plane, characteristic of a Rashba interaction with magnitude approximately 25 meV. Consistent with the presence of intrinsic interfacial electric field we show that the splitting can be enhanced by an applied displacement field in dual gated samples. Giant negative magnetoresistance, up to 75%, and a field induced anomalous Hall effect at magnetic fields < 1 T are observed. These demonstrate that hybridized Au has a magnetic moment and suggests the proximity to formation of a collective magnetic phase. These effects persist close to room temperature.
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The relative twist angle in heterostructures of two-dimensional (2D) materials with similar lattice constants result in a dramatic alteration of the electronic properties. Here, we investigate the electrical and magnetotransport properties in bilayer graphene (BLG) encapsulated between two hexagonal boron nitride (hBN) crystals, where the top and bottom hBN are rotationally aligned with bilayer graphene with a twist angle $theta_tsim 0^{circ} text{and}~ theta_b < 1^{circ}$, respectively. This results in the formation of two moire superlattices, with the appearance of satellite resistivity peaks at carrier densities $n_{s1}$ and $n_{s2}$, in both hole and electron doped regions, together with the resistivity peak at zero carrier density. Furthermore, we measure the temperature(T) dependence of the resistivity ($rho$). The resistivity shows a linear increment with temperature within the range 10K to 50K for the density regime $n_{s1} <n<n_{s2}$ with a large slope d$rho$/dT $sim$ 8.5~$Omega$/K. The large slope of d$rho$/dT is attributed to the enhanced electron-phonon coupling arising due to the suppression of Fermi velocity in the reconstructed minibands, which was theoretically predicted, recently in doubly aligned graphene with top and bottom hBN. Our result establishes the uniqueness of doubly aligned moire system to tune the strength of electron-phonon coupling and to modify the electronic properties of multilayered heterostructures.
Even weak van der Waals (vdW) adhesion between two-dimensional solids may perturb their various materials properties owing to their low dimensionality. Although the electronic structure of graphene has been predicted to be modified by the vdW interaction with other materials, its optical characterization has not been successful. In this report, we demonstrate that Raman spectroscopy can be utilized to detect a few % decrease in the Fermi velocity (vF) of graphene caused by the vdW interaction with underlying hexagonal boron nitride (hBN). Our study also establishes Raman spectroscopic analysis which enables separation of the effects by the vdW interaction from those by mechanical strain or extra charge carriers. The analysis reveals that spectral features of graphene on hBN are mainly affected by change in vF and mechanical strain, but not by charge doping unlike graphene supported on SiO2 substrates. Graphene on hBN was also found to be less susceptible to thermally induced hole doping.
Two-dimensional (2D) crystals, such as graphene, hexagonal boron nitride and transitional metal dichalcogenides, have attracted tremendous amount of attention over the past decade due to their extraordinary thermal, electrical and optical properties, making them promising nano-materials for the next-generation electronic systems. A large number of heterostructures have been fabricated by stacking of various 2D materials to achieve different functionalities. In this work, we simulate the electron transport properties of a three-terminal multilayer heterostructure made from graphene nanoribbons vertically sandwiching a boron nitride tunneling barrier. To investigate the effects of the unavoidable misalignment in experiments, we introduce a tunable angular misorientation between 2D layers to the modeled system. Current-Voltage (I-V) characteristics of the device exhibit multiple NDR peaks originating from distinct mechanisms. A unique NDR mechanism arising from the lattice mismatch is captured and it depends on both the twisting angle and voltage bias. Analytical expressions for the positions of the resonant peaks observed in I-V characteristic are developed. To capture the slight degradation of PVR ratios observed in experiments when temperature increases from 2K to 300K, electron-photon scattering decoherence has been added to the simulation, indicating a good agreement with experiment works as well as a robust preservation of resonant tunneling feature.
Graphene has been identified as a promising material with numerous applications, particularly in spintronics. In this paper we investigate the peculiar features of spin excitations of magnetic units deposited on graphene nanoribbons and how they can couple through a dynamical interaction mediated by spin currents. We examine in detail the spin lifetimes and identify a pattern caused by vanishing density of states sites in pristine ribbons with armchair borders. Impurities located on these sites become practically invisible to the interaction, but can be made accessible by a gate voltage or doping. We also demonstrate that the coupling between impurities can be turned on or off using this characteristic, which may be used to control the transfer of information in transistor-like devices.
Experiments on hexagonal graphene-like structures using microwave measuring techniques are presented. The lowest transverse-electric resonance of coupled dielectric disks sandwiched between two metallic plates establishes a tight-binding configuration. The nearest-neighbor coupling approximation is investigated in systems with few disks. Taking advantage of the high flexibility of the disks positions, consequences of the disorder introduced in the graphene lattice on the Dirac points are investigated. Using two different types of disks, a boron-nitride-like structure (a hexagonal lattice with a two-atom basis) is implemented, showing the appearance of a band gap.
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