β型烧绿石结构氧化物超导体AOs_2O_6(A=K,Rb,Cs)电子能带结构的第一性原理计算

用全势线性缀加平面波方法计算β型烧绿石结构氧化物超导体AOs2O6(A=K,Rb,Cs)的电子能带结构及态密度.计算发现电子自旋轨道耦合和在位库仑势U的作用增大了费米面处态密度值.通过计算还得到这三种化合物电子关联常数λc分别为1.55,1.12和0.73.由实验测量与能带计算得到的电子比热容系数的比值得到电子质量提高参数.通过分析这三种化合物电子质量提高参数,推算出它们的电声子耦合常数λep分别为1.56,0.78和1.08.由此提出KOs2O6为强电子关联和强电声子耦合系统,而RbOs2O6和CsOs2O6的电子关联性与电声子耦合为中等.

电场下应变层量子阱AlN/GaN(001)的子带结构

采用有效质量理论６带模型，研究了电场下应变层量子阱ＡｌＮ／ＧａＮ（００１）的价带子能带结构．具体计算了价带子能级的色散曲线，分析了电场和应变效应对子能带的影响．还计算了不同电场和不同阱宽的空穴子能级．

Highly Sensitive Photodetectors Based on WS_(2) Quantum Dots/GaAs Heterostructures

The performance of the photodetector is significantly impacted by the inherent surface faults in GaAs nanowires(NWs).We combined three-dimensional(3D)gallium arsenide nanowires with zero-dimensional(0D)WS_(2) quantum dot(QDs)materials in a simple and convenient way to form a heterogeneous structure.Various performance enhancements have been realized through the formation of typeⅡenergy bands in heterostructures,opening up new research directions for the future development of photodetector devices.This work successfully fabricated a high-sensitivity photodetector based on WS_(2)QDs/GaAs NWs heterostructure.Under 660 nm laser excitation,the photodetector exhibits a responsivity of 368.07 A/W,a detectivity of 2.7×10^(12)Jones,an external quantum efficiency of 6.47×10^(2)%,a low-noise equivalent power of 2.27×10^(-17)W·Hz^(-1/2),a response time of 0.3 s,and a recovery time of 2.12 s.This study provides a new solution for the preparation of high-performance GaAs detectors and promotes the development of optoelectronic devices for GaAs NWs.

Temperature Dependence of the Energy-Band Structure for the Holstein Molecular-Crystal Model

We study the influences of the temperature on the energy-band structure for the Holstein molecular-crystal model. We show that the energy-band width and the energy-gap width of a solid are relevant to both the interaction between an electron and thermal phonons and to thermal expansion. For a one-dimensional Li atom lattice chain, under the chosen parameters,the width of the ls and 2s energy bands narrows as the temperature increases and the energy-gap width between the two bands widens. These results agree qualitatively with those observed experimentally. Studying temperature dependence of the energy-band structure is of great importance for understanding optical and transporting characteristics of a solid.

Quantum Anti-Zeno Effect in Artificial Quantum Systems

In this paper, we study a quantum anti-Zeno effect （QAZE） purely induced by repetitive measurements for an artificial atom interacting with a structured bath. This bath can be artificially realized with coupled resonators in one dimension and possesses photonic band structure like Bloeh electron in a periodic potential. In the presence of repetitive measurements, the pure QAZE is discovered as the observable decay is not negligible even for the atomic energy level spacing outside of the energy band of the artificial bath. If there were no measurements, the decay would not happen outside of the band. In this sense, the enhanced decay is completely induced by measurements through the relaxation channels provided by the bath. Besides, we also discuss the controversial golden rule decay rates originated from the van Hove＇s singularities and the effects of the counter-rotating terms.

Electronic and Magnetic Properties of Double Perovskite Ca_2CrSbO_6

First-principles calculations have been performed for the study of the electronic band structure and ferromagnetic properties of double perovskite Ca2CrSbO6. The density of states, total energy, spin magnetic moment, and charge density were calculated and analyzed in details. It is found that Ca2CrSbO6 has a stable ferromagnetic ground state and the spin magnetic moment per molecule is about 2.99#B. The chromium contributes the most in the total magnetic moments. The results indicate that Ca2CrSbO6 is half-metallic.

Electronic structure and magnetism of RMn6Sn6 （R=Tb, Dy）

This article reports first-principles band structure calculations for RMn6Sn6 (R= Tb, Dy). The calculation uses the linear muffin-tin orbitals (LMTO) method in the atomic-sphere-approximation (ASA),and yields results showing that both TbMn6Sn6 and DyMn6Sn6 are ferrimagnetic compounds with antiparallel aligned moments of R and Mn atoms. In this research the 4f states of R atoms are treated as localized states,i. e., the hybridization of 4f states with other valence electrons is neglected. The moments of Mn in both compounds were determined to be 2.43μB and 2.38μB, respectively. The considerably small additional moments for Mn from the spin-orbit coupling indicates that the spin-orbital coupling is not dominated for Mn atoms. The total moments of Tb and Dy atoms are 10.28μB and 11.20μB. All the calculation findings accorded well with experimental results.

Electronic and Optical Properties of Rock-Salt A1N under High Pressure via First-Principles Analysis

Electronic and optical properties of rock-salt AIN under high pressure are investigated by first-principlesmethod based on the plane-wave basis set.Analysis of band structures suggests that the rock-salt AIN has an indirectgap of 4.53 eV,which is in good agreement with other results.By investigating the effects of pressure on the energygap,the different movement of conduction band at X point below and above 22.5 GPa is predicted.The opticalproperties including dielectric function,absorption,reflectivity,and refractive index are also calculated and analyzed.Itis found that the rock-salt AIN is transparent from the partially ultra-violet to the visible light area and hardly does thetransparence affected by the pressure.Furthermore,the curve of optical spectrum will shift to high energy area (blueshift) with increasing pressure.

New method of preparing 2D photonic crystals with big scale based on UV photosensitivity

A new method based on UV photosensitivity is proposed to fabricate big scale two dimensional photonic crystal.The optical transmission properties of designed periodic structure are investigated by numerical analysis.The results show that the 2D photonic crystal fabricated by the new method has a desirable photonic bandgap of TE mode.

Band Structure and Electron Transport of Bulk Based on an Ensemble Monte Carlo Calculation

The current demand growth of new components capable of operating at high power, high frequency, high temperatures and convergence towards miniaturization has lead to the development of new fields of nanotechnology based on II-VI semiconductor Interest in nanostructure：s based on II-VI semiconductor narrow gap containing mercury （such as super lattices HgTe/CdTe） was due to their advantages over alloys with cadmium telluride Mercury （MCT： HgCdTe）. The ternary alloy is a semiconductor band-gap direct, in that work the main interest is about the ternary compound. The results obtained are very satisfactory, they are compared with experimental results, and are in good agreement. These results are very promising and open new perspectives for the realization of solar cells and applications in the field of sensors.

Strain-induced direct-indirect bandgap transition and phonon modulation in monolayer WS2

In situ strain photoluminescence （PL） and Raman spectroscopy have been employed to exploit the evolutions of the electronic band structure and lattice vibrational responses of chemical vapor deposition （CVD）-grown monolayer tungsten disulphide （WS2） under uniaxial tensile strain. Observable broadening and appearance of an extra small feature at the longer-wavelength side shoulder of the PL peak occur under 2.5% strain, which could indicate the direct-indirect bandgap transition and is further confirmed by our density-functional-theory calculations. As the strain increases further, the spectral weight of the indirect transition gradually increases. Over the entire strain range, with the increase of the strain, the light emissions corresponding to each optical transition, such as the direct bandgap transition （K-K） and indirect bandgap transition （F-K, ≥2.5%）, exhibit a monotonous linear redshift. In addition, the binding energy of the indirect transition is found to be larger than that of the direct transition, and the slight lowering of the trion dissociation energy with increasing strain is observed. The strain was used to modulate not only the electronic band structure but also the lattice vibrations. The softening and splitting of the in-plane E＇ mode is observed under uniaxial tensile strain, and polarization-dependent Raman spectroscopy confirms the observed zigzag-oriented edge of WS2 grown by CVD in previous studies. These findings enrich our understanding of the strained states of monolayer transition-metal dichalcogenide （TMD） materials and lay a foundation for developing applications exploiting their strain-dependent optical properties, including the strain detection and light-emission modulation of such emerging two-dimensional TMDs.

Growth and low-energy electron microscopy characteri- zation of monolayer hexagonal boron nitride on epitaxial cobalt

Low-energy electron microscopy （LEEM） has been used to study the structure, initial growth orientation, growth progression, and the number of layers of atomically thin hexagonal boron nitride （h-BN） films. The h-BN films are grown on heteroepitaxial Co using chemical vapor deposition （CVD） at low pressure. Our findings from LEEM studies include the growth of monolayer film having two, oppositely oriented, triangular BN domains commensurate with the Co lattice. The growth of h-BN appears to be self-limiting at a monolayer, with thicker domains only appearing in patches, presumably initiated between domain boundaries. Reflectivity measurements of the thicker h-BN films show oscillations resulting from the resonant electron transmission through quantized electronic states of the h-BN films, with the number of minima scaling up with the number of h-BN layers. First principles density functional theory （DFT） calculations show that the positions of oscillations are related to the electronic band structure of h-BN.

Topological flat bands in twisted trilayer graphene

Twisted trilayer graphene(TLG)may be the simplest realistic system so far,which has flat bands with nontrivial topology.Here,we give a comprehensive calculation about its band structures and the band topology,i.e.,valley Chern number of the nearly flat bands,with the continuum model.With realistic parameters,the magic angle of twisted TLG is about 1.12°,at which two nearly flat bands appears.Unlike the twisted bilayer graphene,a small twist angle can induce a tiny gap at all the Dirac points,which can be enlarged further by a perpendicular electric field.The valley Chern numbers of the two nearly flat bands in the twisted TLG depends on the twist angleθand the perpendicular electric field E⊥.Considering its topological flat bands,the twisted TLG should be an ideal experimental platform to study the strongly correlated physics in topologically nontrivial flat band systems.And,due to its reduced symmetry,the correlated states in twisted TLG should be quite different from that in twisted bilayer graphene and twisted double bilayer graphene.

Enhancement of photoresponsive electrical characteristics of multilayer MoS2 transistors using rubrene patches

Multilayer MoS2 is a promising active material for sensing, energy harvesting, and optoelectronic devices owing to its intriguing tunable electronic band structure. However, its optoelectronic applications have been limited due to its indirect band gap nature. In this study, we fabricated a new type of phototransistor using multilayer MoS2 crystal hybridized with p-type organic semiconducting rubrene patches. Owing to the outstanding photophysical properties of rubrene, the device characteristics such as charge mobility and photoresponsivity were considerably enhanced to an extent depending on the thickness of the rubrene patches. The enhanced photoresponsive conductance was analyzed in terms of the charge results of the nanoscale laser confocal time-resolved PL measurements. transfer doping effect, validated by the microscope photoluminescence （PL） and

Photonic band structure of one-dimensional metal/dielectric structures calculated by the plane-wave expansion method

The plane-wave expansion(PWE) method is employed to calculate the photonic band structures of metal/dielectric(M/D) periodic systems. We consider a one-dimensional(1D) M/D superlattice with a metal layer characterized by a frequency-dependent dielectric function. To calculate the photonic band of such a system, we propose a new method and thus avoid solving the nonlinear eigenvalue equations. We obtained the frequency dispersions and the energy distributions of eigen-modes of 1D superlattices. This general method is applicable to calculate the photonic band of a broad class of physical systems, e.g. 2D and 3D M/D photonic crystals. For comparison, we present a simple introduction of the finite-difference(FD) method to calculate the same system, and the agreement turns out to be good. But the FD method cannot be applied to the TM modes of the M/D superlattice.

Ideal Weyl semimetal with 3D spin-orbit coupled ultracold quantum gas

There is an immense effort in search for various types of Weyl semimetals, of which the most fundamental phase consists of the minimal number of i.e. two Weyl points, but is hard to engineer in solids. Here we demonstrate how such fundamental Weyl semimetal can be realized in a maneuverable optical Raman lattice, with which the three-dimensional(3D) spin-orbit(SO) coupling is synthesised for ultracold atoms. In addition, a new novel Weyl phase with coexisting Weyl nodal points and nodal ring is also predicted here, and is shown to be protected by nontrivial linking numbers. We further propose feasible techniques to precisely resolve 3D Weyl band topology through 2D equilibrium and dynamical measurements. This work leads to the first realization of the most fundamental Weyl semimetal band and the 3D SO coupling for ultracold quantum gases, which are respectively the significant issues in the condensed matter and ultracold atom physics.

An Improved Study of Electronic Band Structure and Optical Parameters of X-Phosphides (X=B, Al, Ga, In) by Modified Becke-Johnson Potential

We report the electronic band structure and optical parameters of X-Phosphides （X=B, AI, Ga, In） by first-principles technique based on a new approximation known as modified Becke-Johnson （roB J）. This potential is considered more accurate in elaborating excited states properties of insulators and semiconductors as compared to LDA and GGA. The present calculated band gaps values of BP, AlP, GaP, and InP are 1.867 eV, 2.268 eV, 2.090 eV, and 1.377 eV respectively, which are in close agreement to the experimental results. The band gap values trend in this study is as： E9 （mBJ-GGA/LDA） 〉 E9 （GGA） 〉 Eg （LDA）. Optical parametric quantities （dielectric constant, refractive index, reflectivity and optical conductivity） which based on the band structure are aiso presented and discussed. BP, AlP, GaP, and InP have strong absorption in between the energy range 4-9 eV, 4-7 ev, 3-7 eV, and 2-7 eV respectively. Static dielectric constant, static refractive index and coefficient of reflectivity at zero frequency, within mBJ-GGA, are also calculated. BP, AIP, GaP, and InP show significant optical conductivity in the range 5.2-10 eV, 4.3-8 eV, 3.5- 7.2 eV, and 3.2-8 eV respectively. The present study endorses that the said compounds can be used in opto-electronic applications, for different energy ranges.

Effects of Co doping on electronic structure and electric/magnetic properties of La_(0.1)Bi_(0.9)FeO_3 ceramics

In this work,we report the influence of Co-doping on the electronic band structure,dielectric and magnetic properties of La0.1Bi0.9Fe1-xCoxO3 ceramics.X-ray photoelectron spectroscopy investigation shows that Co dopant can shift the valence band spectrum and core-level lines of constituent elements towards higher bind energy regions simultaneously increase the concentration of oxygen vacancies in ceramics.The effects of dopant are discussed with focus given to the Co-doping induced enhancement of electrical conductivity and resistive switching phenomena.

A magnetoelectric-based broadband vibration energy harvester for powering wireless sensors

Scavenging vibration energy directly from environments is an attractive technique for potentially powering small and/or wireless electronic devices in a smart structure and system.In this paper,a novel broadband vibration energy harvester is designed and analyzed,which consists of three cantilever beams,two magnetoelectric(ME) transducers and a magnetic circuit.A theoretical model is developed to analyze the effects of the structure parameters on the frequency response and the electrical output for achieving the optimal vibration energy harvesting performances.A prototype is fabricated and tested.The experimental results show that the harvester has a bandwidth of 7.2 Hz and an average power of 0.21 mW at an acceleration of 0.2 g(with g=9.8 ms-2).

A Density Functional Theory Study of Codoping Characteristics of Sulfur with Alkaline Earth in Delafossite CuAlO_2

The structural,electronic properties and formation energies of sulfur and alkaline earth codoped delafossite CuAlO_2 have been investigated using the first-principles density functional theory calculations.Our results reveal that the volume of codoping systems increases with the increasing atomic radius of metal atoms.The formation energies under different growth conditions have been calculated,showing that the codoping systems are formed easily under O-rich growth conditions.Electronic band structures and density of states have been obtained.The decreased bandgaps,enhanced covalence and appearance of electron acceptors after codoping are all good for p-type conductivity.