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Register a new userFirst-principles theory of low-energy electron diffraction and quantum interference in few-layer graphene
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We present a computationally efficient method to incorporate density-functional theory into the calculation of reflectivity in low-energy electron microscopy. The reflectivity is determined by matching plane waves representing the electron beams to the Kohn-Sham wave functions calculated for a finite slab in a supercell. We show that the observed quantum interference effects in the reflectivity spectra of a few layers of graphene on a substrate can be reproduced well by the calculations using a moderate slab thickness.
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The inter-Landau level transitions observed in far-infrared transmission experiments on few-layer graphene samples show a behaviour characteristic of the linear dispersion expected in graphene. This behaviour persists in relatively thick samples, and is qualitatively different from that of thin samples of bulk graphite.
Two-dimensional (2D) antimony (Sb, antimonene) recently attracted interest due to its peculiar electronic properties and its suitability as anode material in next generation batteries. Sb however exhibits a large polymorphic/allotropic structural diversity, which is also influenced by the Sbs support. Thus understanding Sb heterostructure formation is key in 2D Sb integration. Particularly 2D Sb/graphene interfaces are of prime importance as contacts in electronics and electrodes in batteries. We thus study here few-layered 2D Sb/graphene heterostructures by atomic-resolution (scanning) transmission electron microscopy. We find the co-existence of two Sb morphologies: First is a 2D growth morphology of layered beta-Sb with beta-Sb(001)||graphene(001) texture. Second are one-dimensional (1D) Sb nanowires which can be matched to beta-Sb with beta-Sb[2-21] perpendicular to graphene(001) texture and are structurally also closely related to thermodynamically non-preferred cubic Sb(001)||graphene(001). Importantly, both Sb morphologies show rotational van-der-Waals epitaxy with the graphene support. Both Sb morphologies are well resilient against environmental bulk oxidation, although superficial Sb-oxide layer formation merits consideration, including formation of novel epitaxial Sb2O3(111)/beta-Sb(001) heterostructures. Exact Sb growth behavior is sensitive on employed processing and substrate properties including, notably, the nature of the support underneath the direct graphene support. This introduces the substrate underneath a direct 2D support as a key parameter in 2D Sb heterostructure formation. Our work provides insights into the rich phase and epitaxy landscape in 2D Sb and 2D Sb/graphene heterostructures.
We demonstrate that surface relaxation, which is insignificant in trilayer graphene, starts to manifest in Bernal-stacked tetralayer graphene. Bernal-stacked few-layer graphene has been investigated by analyzing its Landau level spectra through quantum capacitance measurements. We find that in trilayer graphene, the interlayer interaction parameters were similar to that of graphite. However, in tetralayer graphene, the hopping parameters between the bulk and surface bilayers are quite different. This shows a direct evidence for the surface relaxation phenomena. In spite of the fact that the Van der Waals interaction between the carbon layers is thought to be insignificant, we suggest that the interlayer interaction is an important factor in explaining the observed results and the symmetry-breaking effects in graphene sublattice are not negligible.
We report electron transport studies in an encapsulated few-layer WTe$_2$ at low temperatures and high magnetic fields. The magnetoconductance reveals a temperature-induced crossover between weak antilocalization (WAL) and weak localization (WL) in quantum diffusive regime. We show that the crossover clearly manifests coexistence and competition among several characteristic lengths, including the dephasing length, the spin-flip length, and the mean free path. In addition, low temperature conductance increases logarithmically with the increase of temperature indicating an interplay of electron-electron interaction (EEI) and spin-orbit coupling (SOC). We demonstrate the existences and quantify the strengths of EEI and SOC which are considered to be responsible for gap opening in the quantum spin hall state in WTe2 at the monolayer limit.
We report a systematic first-principles investigation of the influence of different magnetic insulators on the magnetic proximity effect induced in graphene. Four different magnetic insulators are considered: two ferromagnetic europium chalcogenides namely EuO and EuS and two ferrimagnetic insulators yttrium iron garnet (YIG) and cobalt ferrite (CFO). The obtained exchange-splitting varies from tens to hundreds of meV. We also find an electron doping induced by YIG and europium chalcogenides substrates, that shift the Fermi level up to 0.78 eV and 1.3 eV respectively, whereas hole doping up to 0.5 eV is generated by CFO. Furthermore, we study the variation of the extracted exchange and tight binding parameters as a function of the EuO and EuS thicknesses. We show that those parameters are robust to thickness variation such that a single monolayer of magnetic insulator can induce a large magnetic proximity effect on graphene. Those findings pave the way towards possible engineering of graphene spin-gating by proximity effect especially in view of recent experiments advancement.
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