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Edge-dependent reflection and inherited fine structure of higher-order plasmons in graphene nanoribbons
摘要： We investigate higher-order plasmons in graphene nanoribbons, and we present how electronic edge states and wave-function fine structure influence the graphene plasmons. Based on nearest-neighbor tight-binding calculations, we find that a standing-wave model based on nonlocal bulk plasmon dispersion is surprisingly accurate for armchair ribbons of widths even down to a few nanometers, and we determine the corresponding phase shift upon edge reflection and an effective ribbon width. Wider zigzag ribbons exhibit a similar phase shift, whereas the standing-wave model describes few-nanometer zigzag ribbons less satisfactorily, to a large extent because of their edge states. We directly confirm that also the larger broadening of plasmons for zigzag ribbons is due to their edge states. Furthermore, we report a prominent fine structure in the induced charges of the ribbon plasmons, which for armchair ribbons follows the electronic wave-function oscillations induced by intervalley coupling. Interestingly, the wave-function fine structure is also found in our analogous density-functional theory calculations, and both these and tight-binding numerical calculations are explained quite well with analytical Dirac theory for graphene ribbons.
关键词： plasmons,edge states,tight-binding,density-functional theory,Dirac theory,graphene nanoribbons
更新于2025-09-23 15:23:52
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Lateral interfaces of transition metal dichalcogenides: A stable tunable one-dimensional physics platform
摘要： We study in-plane lateral heterostructures of commensurate transition-metal dichalcogenides, such as MoS2-WS2 and MoSe2-WSe2, and find interfacial and edge states that are highly localized to these regions of the heterostructure. These are one-dimensional (1D) in nature, lying within the band gap of the bulk structure and exhibiting complex orbital and spin structure. We describe such heteroribbons with a three-orbital tight-binding model that uses first principles and experimental parameters as input, allowing us to model realistic systems. Analytical modeling for the 1D interfacial bands results in long-range hoppings due to the hybridization along the interface, with strong spin-orbit couplings. We further explore the Ruderman-Kittel-Kasuya-Yosida indirect interaction between magnetic impurities located at the interface. The unusual features of the interface states result in effective long-range exchange noncollinear interactions between impurities. These results suggest that transition-metal dichalcogenide interfaces could serve as stable, tunable 1D platform with unique properties for possible use in exploring Majorana fermions, plasma excitations, and spintronics applications.
关键词： spin-orbit coupling,interface states,transition metal dichalcogenides,RKKY interaction,tight-binding model,lateral heterostructures
更新于2025-09-23 15:23:52
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[IEEE 2018 International Conference on Simulation of Semiconductor Processes and Devices (SISPAD) - Austin, TX, USA (2018.9.24-2018.9.26)] 2018 International Conference on Simulation of Semiconductor Processes and Devices (SISPAD) - The Impact of Dopant Diffusion on Random Dopant Fluctuation in Si Nanowire FETs: A Quantum Transport Study
摘要： In this work, we perform statistical quantum transport simulations with 3×3 nm2 Si nanowire (NW) field-effect transistors (FETs) to investigate the impact of dopant diffusion on random dopant fluctuation. First, we use an effective mass Hamiltonian for the transport where the confinement and transport effective masses are extracted from the tight-binding band structure calculations. The dopant diffusion along the transport direction from the source/drain regions to the channel region is modeled by the Gaussian doping profile. To generate random discrete dopants, we adopt a rejection scheme considering the 3-dimensional atomic arrangement of the NW structures. Our statistical simulation results show that the diffused dopants into the channel region cause large variability problems in Si NW FETs.
关键词： non-equilibrium Green's function,tight-binding,dopant diffusion,random discrete dopants,silicon nanowire
更新于2025-09-23 15:22:29
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Valley engineering by strain in Kekulé-distorted graphene
摘要： A Kekulé bond texture in graphene modi?es the electronic band structure by folding the Brillouin zone and bringing the two inequivalent Dirac points to the center. This can result in the opening of a gap (Kek-O) or the locking of the valley degree of freedom with the direction of motion (Kek-Y). We analyze the effects of uniaxial strain on the band structure of Kekulé-distorted graphene for both textures. Using a tight-binding approach, we introduce strain by considering the hopping renormalization and corresponding geometrical modi?cations of the Brillouin zone. We numerically evaluate the dispersion relation and present analytical expressions for the low-energy limit. Our results indicate the emergence of a Zeeman-like term due to the coupling of the pseudospin with the pseudomagnetic strain potential which separates the valleys by moving them in opposite directions away from the center of the Brillouin zone. For the Kek-O phase, this results in a competition between the Kekulé parameter that opens a gap and the magnitude of strain which closes it, while for the Kek-Y phase, it results in a superposition of two shifted Dirac cones. As the Dirac cones are much closer in the superlattice reciprocal space than in pristine graphene, we propose strain as a control parameter for intervalley scattering.
关键词： Brillouin zone,tight-binding,strain,graphene,valley engineering,Kekulé distortion
更新于2025-09-23 15:22:29
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Integral Characteristics of Wave Packets in the Problem of the Evolution of A Wave Function on A One-Dimensional Lattice
摘要： We consider the quantum dynamics of charge transfer on a lattice in the tight-binding approximation and analytically calculate the integral characteristics of the wave packet propagating along the lattice. We focus on calculating the mean and root-mean-square displacements. We also obtain expressions for higher-order moments as series for squares of Bessel functions, which might be independently interesting.
关键词： moments of distribution function,quantum dynamics,tight-binding approximation
更新于2025-09-23 15:22:29
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Bond versus charge disproportionation in the bismuth perovskites
摘要： We develop a theory describing a parameter-based phase diagram to be associated with materials incorporating skipped-valence ions [Phys. Rev. Lett. 61, 2713 (1988)]. We use a recently developed tight-binding approach for the bismuthates to study the phase diagram exhibiting a crossover from a bond disproportionated (BD) to a charge disproportionated (CD) system in addition to the presence of a new metallic phase. We argue that three parameters determine the underlying physics of the BD-CD crossover when electron correlation effects are small: the hybridization between O-2pσ and Bi-6s orbitals (tspσ ), the charge-transfer energy between Bi-6s and O-a1g molecular orbitals ((cid:2)), and the width of the oxygen sublattice band (W ). In the BD system, we estimate the effective attractive interaction U between the two holes on the same hybrid A1g orbital composed of a linear combination of O-a1g and Bi-6s orbitals. Although we concentrate here on the example of the bismuthates, the basic ideas can be directly transferred to other perovskites with negative charge-transfer energy, like ReNiO3 (Re: rare-earth element), Ca(Sr)FeO3, CsTIF3, and CsTlCl3.
关键词： phase diagram,bismuth perovskites,tight-binding model,bond disproportionation,charge disproportionation
更新于2025-09-23 15:21:21
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Hopping parameters for tunnel coupling in 2D materials
摘要： Using Bardeen’s approach and orbital wave functions obtained by the algorithm of Herman and Skillman, we calculated interatomic matrix elements for tunnel interaction between the atoms from the set of B, C, N, Si, P, S, Ti, V, Se, Mo, Te and W, which constitute many 2D materials. In a wide range of interatomic distances, these values are approximated by simple functions with a small set of parameters. The results are presented in reference tables. These results will be useful for describing different tunnel phenomena in low-dimensional materials using the tight-binding approach.
关键词： tunnel coupling,2D materials,interatomic matrix elements,Bardeen’s approach,tight-binding approach
更新于2025-09-23 15:21:21
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revealed by angle-resolved photoemission spectroscopy
摘要： We revisit charge density wave (CDW) behavior in the archetypal quasi-one-dimensional (quasi-1D) material NbSe3 by high-resolution angle-resolved photoemission spectroscopy measurements utilizing a microfocused laser with a photon energy of 6.3 eV. We present a detailed view of the electronic structure of this complex multiband system and unambiguously resolve CDW gaps at the Fermi level (EF). By employing a tight-binding model, we argue that these gaps are the result of interband coupling between electronic states that reside predominantly on distinct 1D chains within the material. Two such localized states are found to couple to an electronic state that extends across multiple 1D chains, highlighting the importance of a higher-dimensional interaction in stabilizing the CDW ordering in this material. In addition, the temperature evolution of intrachain gaps caused by the CDW periodicities far below EF deviate from the behavior expected for a Peierls-type mechanism driven by nesting; the upper and lower bands of the renormalized CDW dispersions maintain a fixed peak-to-peak distance while the gaps are gradually removed at higher temperatures. This points toward a gradual loss of long-range phase coherence as the dominant effect in reducing the CDW order parameter, which may correspond to the loss of coherence between the coupled chains. Furthermore, one of the gaps is observed above the bulk and surface CDW transition temperatures, implying the persistence of short-range incoherent CDW order. The influence of such higher-dimensional interactions likely plays an important role in a range of low-dimensional systems.
关键词： angle-resolved photoemission spectroscopy,tight-binding model,charge density wave,phase coherence,interband coupling,quasi-one-dimensional,NbSe3
更新于2025-09-23 15:21:01
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[IEEE 2018 IEEE International Conference on Electron Devices and Solid State Circuits (EDSSC) - Shenzhen (2018.6.6-2018.6.8)] 2018 IEEE International Conference on Electron Devices and Solid State Circuits (EDSSC) - Local Modification of Defective Edge Hamiltonian for Graphene Nanoribbon Devices
摘要： The impact of edge defect on C-C bond is revealed to be localized in short range by ab initio calculation. Thus we propose a the tight-bind (TB) Hamiltonian. Except for the edge parameter correction, local C-C bond distortion and the diversity of different armchair GNRs. It is demonstrated that this method significantly reduces TB fitting errors with two typical GNR edge defects. In addition, using the modified Hamiltonian, device simulation results are shown.
关键词： tight-binding (TB) Hamiltonian,local modification,Graphene nanoribbon FETs (GNR FETs),edge defect
更新于2025-09-23 15:21:01
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Valley polarization reversal and spin ferromagnetism and antiferromagnetism in quantum dots of the topological insulator monolayer bismuthene on SiC
摘要： The valley and spin polarizations associated with electronic transport in quantum dots of the large-gap topological insulator (TI) monolayer bismuthene on SiC are investigated in the linear response regime using a minimal tight-binding model that accurately describes the low-energy electronic band structure of this TI. It is found that for zigzag edges the electronic edge states are strongly valley polarized if the Fermi energy lies in the bulk energy band gap. We predict the edge-state valley polarizations to switch between valleys K and K (cid:2) as the Fermi energy varies from the top of the valence band to the bottom of the conduction band or if the direction of electric current through the dot is reversed. If the electrostatic potential in the dot is nonuniform, we predict that the valley polarization of an electron can reverse as it travels through the dot. The valley polarization reversal is due to the zigzag edge-state dispersion crossing the center of the Brillouin zone that separates valleys K and K (cid:2) and is therefore predicted to be a general phenomenon. Although the spin polarization within the edge states is ferromagnetic, as expected for spin Hall devices, our calculations reveal the out-of-plane component of the spin polarization of the bulk valence band scattering states to be antiferromagnetic, and the direction of the out-of-plane component of the Neel vector to depend on whether the electronic accumulation belongs primarily to valley K or K (cid:2).
关键词： quantum dots,ferromagnetism,bismuthene,topological insulator,spin polarization,antiferromagnetism,SiC,tight-binding model,valley polarization
更新于2025-09-23 15:19:57