1,721,144 research outputs found
Massive Dirac quasiparticles in the optical absorbance of graphene, silicene, germanene, and tinene
No full textWe present first-principles studies of the optical absorbance of the group IV honeycomb crystals graphene, silicene, germanene, and tinene. We account for many-body effects on the optical properties by using the non-local hybrid functional HSE06. The optical absorption peaks are blueshifted due to quasiparticle corrections, while the influence on the low-frequency absorbance remains unchanged and reduces to a universal value related to the Sommerfeld fine structure constant. At the Dirac points spin-orbit interaction opens fundamental band gaps; parabolic bands with a very small effective mass emerge. Consequently, the low-frequency absorbance is modified with a spin-orbit-induced transparency region and an increase of the absorbance at the fundamental absorption edge
Optical properties of two-dimensional honeycomb crystals graphene, silicene, germanene, and tinene from first principles
Full text linkWe compute the optical conductivity of 2D honeycomb crystals beyond the usual Dirac-cone approximation. The calculations are mainly based on the independent-quasiparticle approximation of the complex dielectric function for optical interband transitions. The full band structures are taken into account. In the case of silicene, the influence of excitonic effects is also studied. Special care is taken to derive converged spectra with respect to the number of k points in the Brillouin zone and the number of bands. In this way both the real and imaginary parts of the optical conductivity are correctly described for small and large frequencies. The results are applied to predict the optical properties reflection, transmission and absorption in a wide range of photon energies. They are discussed in the light of the available experimental data
Beyond graphene: Clean, hydrogenated and halogenated silicene, germanene, stanene, and plumbene
No full textThe fascinating electronic and optoelectronic properties of freestanding graphene and the possible inclusion of novel two-dimensional (2D) systems in silicon-based electronics have driven the search for atomic layers consisting of other group-IV elements Si, Ge, Sn, and Pb, which form similar hexagonal lattices and are isoelectronic to graphene. The resulting 2D crystals silicene, germanene, stanene and plumbene, referred as Xenes, but also their functionalized counterparts, e.g. the hydrogenated sheet crystals, named as Xanes, silicane, germanane, and stanane, are in the focus of this review article. In addition, halogenated Xenes are investigated. The consequences of the larger atomic radii on the atomic geometry, the energetic stability, and possible epitaxial preparations are discussed. In the case of honeycomb atomic arrangements, the low-energy electronic excitations are ruled by almost linear bands. Spin–orbit coupling opens small gaps leading to Dirac fermions with finite effective masses. The linear bands give rise to an absorbance of the Xenes determined by the finestructure constant in the long-wavelength regime. While for vanishing photon energies the excitonic influence is still an open question, saddle-point excitons and excitons at M0 van Hove singularities appear at higher frequencies. After opening substantial fundamental gaps by hydrogenation, the absorption edges of the Xanes, silicane, germanane, and stanane, are dominated by bound excitons with extremely large binding energies. Other chemical functionalizations, but also vertical electric fields, yield electronic structures ranging from topological to trivial insulators. Even a quantum spin Hall phase is predicted at room temperature. The topological character and the possible quantization of the spin Hall conductivity are studied versus gap inversion, chemical functionalization, and Rashba spin–orbit interaction. The drastic changes of the electronic properties of Xenes with chemical functionalization, interaction with the substrate, and external perturbations, open future opportunities for tailoring fundamental properties and, therefore, interesting applications in novel electronic and optoelectronic nanodevices
Electronic and Optical properties of cadmium fluoride: the role of many-body effects
No full textElectronic and Optical properties of cadmium fluoride: the role of many-body effect
Efficient quasiparticle band-structure calculations for cubic and non cubic crystals
No full textAn efficient method developed for the calculation of quasiparticle corrections to densityfunctional-
theory —local-density-approximation (DFT-LDA) band structures of diamond and zincblende
materials is generalized for crystals with other cubic, hexagonal, tetragonal, and orthorhombic
Bravais lattices. Local-field efFects are considered in the framework of a LDA-like approximation.
The dynamical screening is treated by expanding the self-energy linearly in energy. The anisotropy
of the inverse dielectric matrix is taken into account. The singularity of the Coulomb potential in
the screened-exchange part of the electronic self-energy is treated using auxiliary functions of the
appropriate symmetry. An application to the electronic quasiparticle band structure of wurtzite 2HSiC
is presented within the approach of norm-conserving, nonlocal, fully separable pseudopotentials
and a plane-wave expansion of the wave functions for the underlying DFT-LDA
Electronic and optical properties of topological semimetal Cd3As2
Full text linkUsing ab initio density functional theory the band structure and the dielectric function of a bct Cd3As2 crystal are calculated. We find a Dirac semimetal with two Dirac nodes k± near the Γ point on the tetragonal axis. The bands near the Fermi level exhibit a linear behavior. The resulting Dirac cones are anisotropic and the electron-hole symmetry is destroyed along the tetragonal axis. Along this axis the symmetry-protected band linearity only exists in a small energy interval. The Dirac cones seemingly found by ARPES in a wider energy range are interpreted in terms of pseudo-linear bands. The behavior as 3D graphene-like material is traced back to As p orbital pointing to Cd vacancies, in directions which vary throughout the unit cell. Because of the Dirac nodes the dielectric functions (imaginary part) show a plateau for vanishing frequencies whose finite value is proportional to the Sommerfeld fine structure constant but varies with the light polarization. The consequences of the anisotropy of the Dirac cones are highlighted for the polarization dependence of the infrared optical conductivity
GIANT QUASI-PARTICLE SHIFTS OF SEMICONDUCTOR SURFACE-STATES
No full textThe differences between the energy positions of surface bands in quasi-particle and local-density approximations are calculated taking into account the different screening properties of a semiconductor and of an electron gas of the same average density. Gap corrections of the order of 1.5 eV are computed for GaP(110) and GaAs(110) surfaces, in good agreement with experiment
Reliable estimates of quasi-particle and excitonic effects in clusters through DVM total energy calculations
No full textTheoretical study of As overlayers on InP(110) surface: optical properties
No full textThe reflectance anisotropy of the As/InP(110) surface is calculated by using an ab initio plane-wave pseudopotential method. We analyze different models of As coverage, ranging from non-reacted epitaxial layers to exchange-reacted geometries. Comparison with experimental data confirms that the annealed, highly ordered surface phase can be described by an InAs monolayer on the InP substrate (exchange reacted model), whereas the reflectance anisotropy of the as-grown, poorly ordered As/InP surface probably is dominated by disorder effects. (C) 1998 Elsevier Science B.V. All rights reserved
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