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Movement of dirac points and band gaps in graphyne under rotating strain

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Nano Research 2017年第6期10卷 2005-2020页

作者： Zhenzhu Li Zhongfan Liu Zhirong Liu College of Chemistry and Molecular Engineering Center for Nanochemistry State Key Laboratory for Structure Chemistry of Unstableand Stable Species and Beijing National Laboratory for Molecular Sciences (BNLMS) Peking University Beijing 100871 China

The introduction of lattice anisotropy causes dirac cones to shift in response to the applied strain, leaving a pseudogap at the original dirac points. Here, a group-theory analysis is combined with first-principles calculations to reveal the movement characteristics of dirac points and band gaps in various graphynes under rotating uniaxial and shear strains. Graphene, where linear effects dominate, is different from α-,β-, and γ-graphynes, which generate strong nonlinear responses due to their bendable acetylenic linkages. However, the linear components of the electronic response, which are essential in determining material performance such as intrinsic carrier mobility due to electron-phonon coupling, can be readily separated, and are well described by a unified theory. The movement of the dirac points in α-graphyne is circular under a rotating strain, and the pseudogap opening is isotropic with a magnitude of only 2% that in graphene. In comparison, the movement in β-graphyne is elliptical and the center is displaced from the origin. For γ-graphyne, three branches of gaps change with the applied strains with a sine/cosine dependence on the strain angle. The developed methodology is useful in determining the electronic response to various strains of dirac materials and two-dimensional semiconductors,

关键词： graphene graphyne dirac point band gap first-principles strain effect

Light response and adsorption interaction of black phosphorus quantum dots and single‑layer graphene phototransistor

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Frontiers of Optoelectronics 2023年第2期16卷 15-23页

作者： Qi Han Yadong Jiang Xianchao Liu Chaoyi Zhang Jun Wang School of Optoelectronic Science and Engineering University of Electronic Science and Technology of ChinaChengdu 610054China State Key Laboratory of Electronic Thin Films and Integrated Devices University of Electronic Science and Technology of ChinaChengdu 610054China

Black phosphorus quantum dots(BPQDs)are synthesized and combined with graphene *** fabricated BPQDs/graphene devices are capable of detecting visible and near infrared *** adsorption efect of BPQDs in graphene is clarifed by the relationship of the photocurrent and the shift of the dirac point with diferent *** dirac point moves toward a neutral point under illumination with both SiO_(2)/Si and Si(3)N_(4)/Si substrates,indicating an anti-doped feature of *** our knowledge,this provides the frst observation of photoresist induced photocurrent in such *** the infuence of the photoresist the device can respond to infrared light up to 980 nm wavelength in vacuum in a cryostat,in which the photocurrent is positive and photoconduction efect is believed to dominate the ***,the adsorption efect is modeled using a frst-principle method to give a picture of charge transfer and orbital contribution in the interaction of phosphorus atoms and single-layer graphene.

关键词： Black phosphorus quantum dots dirac point Photoconduction Adsoprtion

Polyelectrolyte multilayer electrostatic gating of graphene field-effect transistors

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Nano Research 2014年第11期7卷 1650-1658页

作者： Yung Yu Wang Peter J. Burke Department of Chemical Engineering and Materials Science University of California Irvine Irvine California 92697 USA Department of Electrical Engineering and Computer Science University of California Irvine Irvine California 92697 USA

We apply polyelectrolyte multilayer films by consecutive alternate adsorption of positively charged polyallylamine hydrochloride and negatively charged sodium polystyrene sulfonate to the surface of graphene field effect transistors. Oscillations in the dirac voltage shift with alternating positive and negative layers clearly demonstrate the electrostatic gating effect in this simple model system. A simple electrostatic model accounts well for the sign and magnitude of the dirac voltage shift. Using this system, we are able to create p-type or n-type graphene at will. This model serves as the basis for understanding the mechanism of charged polymer sensing using graphene devices, a potentially technologically important application of graphene in areas such as DNA sequencing, biomarker assays for cancer detection, and other protein sensing applications.

关键词： dirac point graphene transistor electrostatic gating polyallylaminehydrochloride (PAH) sodium polystyrenesulfonate (PSS)

Photonic dirac cone and topological transition in a moving dielectric slab

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Chinese Physics B 2023年第10期32卷 672-677页

作者：潘昕阳李海涛董为杰周萧溪王钢侯波 School of Physical Science and Technology&Collaborative Innovation Center of Suzhou Nano Science and Technology Soochow UniversitySuzhou 215006China School of Optical and Electronic Information Suzhou City UniversitySuzhou 215104China Wave Functional Metamaterial Research Facility The Hong Kong University of Science and TechnologyGuangzhou 511400China

The moving media theory is applied to a photonic confined structure which is a continuous dielectric slab waveguide with the uniaxial anisotropy and without the discrete translational *** moving effect not only brings about non-reciprocity to the whole photonic band structure in the co-moving and counter-moving directions,but also leads to the topological transition of local degenerate points within the band *** demonstrate through calculation that the type-Ⅱdirac point can be turned into type-Ⅰdirac point when the uniaxial slab is moving over certain *** results provide a new approach to regulate the topology of degeneracy for two-dimensional photonic bands in the continuous translational symmetry condition.

关键词： dirac point transition moving guided mode

Topological states switching and group velocity control in two-dimensional non-reciprocal Hermitian photonic lattice

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Chinese Physics B 2023年第11期32卷 56-62页

作者：林宇王元旦杨俊豪符艺萱齐新元 School of Physics Northwest UniversityXi’an 710127China

We proposed a model with non reciprocal coupling coefficients, in which the imaginary parts γ indicate the phase delay or exceed term. The distributions of band structure and the group velocity are both characterized as a function of the coupling. we studied the system’s topological states and group velocity control. The results show that the movement and breaking of dirac points exist in the energy band of the system. By changing the coupling coefficients, the conversion between any topological states corresponds to different Chern number. Topological edge states exist in topological nontrivial systems that correspond to the two different Chern numbers. Besides, it is also found that both the coupling coefficient and the wave vector can cause the oscillation of the pulse group velocity. At the same time, the topological state can suppress the amplitude of the group velocity profiles. Our findings enrich the theory of light wave manipulation in high-dimensional photonic lattices and provide a novel view for realizing linear localization and group velocity regulation of light waves,which has potential application in high-speed optical communication and quantum information fields.

关键词： dirac point imaginary coupling Chern number group velocity

Novel carbon nanotubes from 6,6,12-Graphyne

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Novel carbon nanotubes from 6,6,12-Graphyne