Symmetry Points Of Brillouin Zone Research Articles

Investigations of Optical Functions and Optical Transitions of 2D Semiconductors by Spectroscopic Ellipsometry and DFT.

Optical functions and transitions are essential for a material to reveal the light-matter interactions and promote its applications. Here, we propose a quantitative strategy to systematically identify the critical point (CP) optical transitions of 2D semiconductors by combining the spectroscopic ellipsometry (SE) and DFT calculations. Optical functions and CPs are determined by SE, and connected to DFT band structure and projected density of states via equal-energy and equal-momentum lines. The combination of SE and DFT provides a powerful tool to investigate the CP optical transitions, including the transition energies and positions in Brillouin zone (BZ), and the involved energy bands and carries. As an example, the single-crystal monolayer WS2 is investigated by the proposed method. Results indicate that six excitonic-type CPs can be quantitatively distinguished in optical function of the monolayer WS2 over the spectral range of 245-1000 nm. These CPs are identified as direct optical transitions from three highest valence bands to three lowest conduction bands at high symmetry points in BZ contributed by electrons in S-3p and W-5d orbitals. Results and discussion on the monolayer WS2 demonstrate the effectiveness and advantages of the proposed method, which is general and can be easily extended to other materials.

First-Principles Study of the Optical Properties of Zinc Antimonide Using the mBJ Approximation

This computational study focused on the optical properties of zinc antimonide ZnSb. It relates to the complex dielectric function ε (ω), the refractive index n (ω), the extinction function k (ω), the optical conductivity σ (ω), the reflectivity R(ω), the absorption coefficient α (ω) and the energy loss spectrum L(ω). These properties are calculated and discussed for a growing energy of the incident electromagnetic radiation ranging from 0 to 14 eV, comprising infrared, visible and ultraviolet regions. All these properties are obtained using the Full Potential Linearized Augmented Plane Wave (FP-LAPW), by solving Kohn-Sham equations. This method based on Density Functional Theory (DFT), implemented in Wien2k simulation package. This compound is already used in photo-optical applications, it is for this reason that we interested in the calculation of its optical properties according to the energy of the incident photons, in order to open up for it other use ways. Since the zinc antimonide ZnSb is a semiconductor, its optical properties are investigated using Generalized Gradient Approximation plus modified Becke–Johnson as the exchange correlation (GGA-mBJ). Our calculations are performed by considering only the interband transition of electrons between the occupied states in valence band and unoccupied conduction band states along high symmetry points in Brillouin zone. In addition, the relations of the optical properties to these transitions are discussed in detail. We have also verified the Penn’s model by showing the inverse relationship between the static real part of dielectric function ε1(0) and the optical band gap Eg. The results obtained are compared with other results existing in the literature.

Electron transport in NH3/NO2 sensed buckled antimonene

The structural and electronic properties of buckled antimonene have been analysed using density functional theory based ab-initio approach. Geometrical parameters in terms of bond length and bond angle are found close to the single ruffle mono-layer of rhombohedral antimony. Inter-frontier orbital analyses suggest localization of lone pair electrons at each atomic centre. Phonon dispersion along with high symmetry point of Brillouin zone does not signify any soft mode. With an electronic band gap of 1.8eV, the quasi-2D nano-surface has been further explored for NH3/NO2 molecules sensing and qualities of interaction between NH3/NO2 gas and antimonene scrutinized in terms of electronic charges transfer. A current-voltage characteristic has also been analysed, using Non Equilibrium Green's function (NEGF), for antimonene, in presence of incoming NH3/NO2 molecules.

Research progress of topological quantum states in iron-based superconductor

Iron-based superconductors and topological quantum states have been two important research frontiers in condensed matter physics in recent years. It is a very significant question whether the nontrivial topological phenomena can occur in iron-based superconductors. In this paper, the basic characteristics of the electronic structure of iron-based superconducting are analyzed from three aspects:crystal symmetry, effective model near the high symmetry points in Brillouin zone, and spin-orbit coupling interaction. On this basis, this paper focuses on how the nontrivial topological quantum states occur in the normal state, the states with long-range order near superconducting state and the superconducting state. Furthermore, the relevant theoretical models and results are introduced in detail, the related experimental progress is reviewed, and the development in this field is prospected.

Analysis of linear defect modes in two-dimensional photonic lattices by employing Brillouin zone spectroscopy

The formation of defect modes in optically induced photonic lattices with one_and two_dimensional defects are analyzed by combining the diffraction relationship of uniform lattices and the Brillouin zone spectra. The defect modes associated with different high symmetry points in Brillouin zone are obtained, including the positive and negative defect modes bifurcating from the X1 point, which is “embedded” in the photonic bandgap. It is revealed that, for two_dimensional defects, the positive （negative） defect modes exist only in the regions corresponding to normal （anomalous） diffraction along both principal axes in k-space, whereas for one_dimensional defects, the positive （negative） defect modes can exist in the regions corresponding to normal （anomalous） diffraction along a single direction. The positive defect mode at X1 point predicates the existence of in-band solitons under self-focusing nonlinearity. The conclusions obtained above could be helpful to understanding the formation of lattice solitons （especially in_band solitons） in photonic lattices.

Semi-empirical tight binding modelling of CdSTe/CdTe, ZnSSe/ZnSe and ZnSSe/ CdSe heterostructures

We present a semi-empirical sp 3s ⁎ tight binding model to calculate the effects of alloy composition and strain on electronic band structure of Cd and Zn based group II–VI heterostructures for photovoltaic devices. The semi-empirical sp 3 s ⁎ TB model Hamiltonian includes second nearest neighbor interactions and spin-orbit splitting of p-states. Bond lengths and atomic energies of cation and anion forming ternary semiconductors are taken as nonlinear function of composition. The 2NN sp 3 s ⁎ tight binding model calculations are compared with those of the package program WIEN2k which uses the generalized gradient approximation (GGA) and local spin density approximation (LSDA) based scaling law for the scissor operator for the self energy corrections to the DFT energy band gaps of semiconductors. We found that both the GGA and LSDA corrected WIEN 2k simulations and 2NN sp 3 s ⁎ TB model accurately reproduces the band gaps and both the valence band and conduction band dispersion curves at Γ, X and L high symmetry points of Brillouin zone, also in good agreement with experiment.