Pr替位式掺杂GaAs光电性能的第一性原理研究

采用密度泛函理论下的平面波赝势方法,建立GaAs及Pr-GaAs模型并对其能带结构与吸收光谱进行计算。结果表明稀土Pr的4f态电子使得GaAs的能带结构发生改变,价带电子跃迁至导带所需的激发能减小,吸收光谱发生红移,从而提高了GaAs作为光电材料时对太阳光的利用率。     

抱箍法施工技术在道路桥梁工程中的应用

在道路桥梁工程中应用抱箍法施工技术,能够有效地使施工成本低价、施工质量得到提升,而且还具有符合道路桥梁结构的美观的需求。文章通过在某一道路桥梁中实施抱箍法施工技术,探讨应用抱箍法技术的施工方法,希望能对类似的工程起到借鉴作用。     

Electronic structures and topological properties in nickelates Lnn+1NinO2n+2

After the significant discovery of the hole-doped nickelate compound Nd_0.8Sr_0.2NiO₂, analyses of the electronic structure, orbital components, Fermi surfaces and band topology could be helpful to understand the mechanism of its superconductivity. Based on first-principle calculations, we find that Ni states contribute the largest Fermi surface. The states form an electron pocket at Γ, while 5d_xy states form a relatively bigger electron pocket at A. These Fermi surfaces and symmetry characteristics can be reproduced by our two-band model, which consists of two elementary band representations: B_1g@1a ⊕ A_1g@1b. We find that there is a band inversion near A, giving rise to a pair of Dirac points along M-A below the Fermi level upon including spin-orbit coupling. Furthermore, we perform density functional theory based Gutzwiller (DFT+Gutzwiller) calculations to treat the strong correlation effect of Ni 3d orbitals. In particular, the bandwidth of has been renormalized largely. After the renormalization of the correlated bands, the Ni 3d_xy states and the Dirac points become very close to the Fermi level. Thus, a hole pocket at A could be introduced by hole doping, which may be related to the observed sign change of the Hall coefficient. By introducing an additional Ni 3d_xy orbital, the hole-pocket band and the band inversion can be captured in our modified model. Besides, the nontrivial band topology in the ferromagnetic two-layer compound La₃Ni₂O₆ is discussed and the band inversion is associated with Ni and La 5d_xy orbitals.     

一维铝/铅匀直杆状声子晶体带隙特性分析

通过单一改变组分材料铝或者铅的密度,以及单一改变晶格常数的取值来调节一维铝/铅匀直杆状声子晶体的带隙分布情况。结果表明：该声子晶体中,当单一增大每种材料的密度时,散射体与基体材料的密度差值增大,其入射波散射就更为强烈,也就越容易产生低频带隙;当单一增大声子晶体的晶格常数,即增加复合结构的长度时,入射波散射得就越多,透射波就越来越少,该声子晶体带隙便呈现出向低频率区域靠近的特性。     

宽带环形阻抗变换器的设计

通常在工作频率达几百兆赫、带宽要求大于倍频程带宽的电路中，需要其带宽甚高频放大器的50Ω（或75Ω）输入阻抗与输出阻抗300Ω的传输线实现阻抗匹配．这在移动式电台和闭路电视传输系统中尤其显得重要．     

超宽带缝隙螺旋天线仿真与教学应用研究

改革微波技术与天线实验课程实验教学模式,采用全波电磁仿真软件,设计和仿真了超宽带缝隙结构的平面等角螺旋天线和阿基米德螺旋天线。设计的两种天线都采用同轴电缆直接馈电的方式,结构简单,易于实现。优化和仿真结果表明,在0.4~2GHz的频率范围内,这两种天线的输入电压驻波比小于2,方向图和增益等指标均达到了设计要求,适合于实际应用。仿真结果展示了全波电磁仿真软件的应用效果。     

Ideal type-II Weyl points in topological circuits

Weyl points (WPs), nodal degenerate points in three-dimensional (3D) momentum space, are said to be ‘ideal’ if they are symmetry-related and well-separated, and reside at the same energy and far from nontopological bands. Although type-II WPs have unique spectral characteristics compared with type-I counterparts, ideal type-II WPs have not yet been reported because of a lack of an experimental platform with enough flexibility to produce strongly tilted dispersion bands. Here, we experimentally realize a topological circuit that hosts only topological bands with a minimal number of four ideal type-II WPs. By stacking two-dimensional (2D) layers of inductor-capacitor (LC) resonator dimers with the broken parity inversion symmetry (P), we achieve a strongly tilted band structure with two group velocities in the same direction, and topological surface states in an incomplete bandgap. Our results establish an ideal system for the further study of Weyl physics and other exotic topological phenomena.     

CdS插层层状BiOCl的第一性原理计算

构建了CdS插层层状BiOCl晶胞（CdS-BiOCl）。基于第一性原理对CdS-BiOCl的结构进行了优化计算,在此基础上,计算并分析了 CdS-BiOCl 的电子结构以及光学性质。结果表明,在 CdS-BiOCl 中,Cd同时与两个Cl、两个S原子形成共价键而致a、b轴缩短,c轴拉长;与BiOCl相比,CdS-BiOCl为直接带隙半导体,价带顶因S3p电子参与杂化而提升并致带隙变窄,所有光学性质均发生红移,其峰值均有所降低。     

不同介质形态对石墨结构光子晶体带隙的影响

利用平面波法研究了不同介质形态对二维石墨结构光子晶体的TE偏振模式带隙和TM偏振模式带隙的影响。研究发现,改变构成二维石墨结构光子晶体的介质柱的形态,分别选用圆柱、三角柱、矩柱、五角柱、六角柱等形态,在填充面积比相等时,石墨结构光子晶体的TE和TM两种偏振模式光子带隙都保持不变。     

Research progress on Fabry-Perot resonator antenna

The Fabry-Perot resonator （FPR） antenna has found wide applications in microwave and millimeter waves and recently attracted considerable interest. In this paper, a summary of planar and cylindrical structures, analytic models and research development is presented, and a comparison between these structures and analytic models is made, showing that such analytic models as the FP cavity mode, electromagnetic band gap （EBG） defect mode, transmission line mode, and leaky-wave mode are consistent when applied to analyze this type of resonator antenna. Some interesting topics under recent research, including dual or multi-band, improvement of gain bandwidth, low profile and beam control, are surveyed.