Surface superconductivity in the type II Weyl semimetal TaIrTe4

The search for unconventional superconductivity in Weyl semimetal materials is currently an exciting pursuit, since such superconducting phases could potentially be topologically non-trivial and host exotic Majorana modes. The layered material TaIrTe₄ is a newly predicted time-reversal invariant type II Weyl semimetal with the minimum number of Weyl points. Here, we report the discovery of surface superconductivity in Weyl semimetal TaIrTe₄. Our scanning tunneling microscopy/spectroscopy (STM/STS) visualizes Fermi arc surface states of TaIrTe₄ that are consistent with the previous angle-resolved photoemission spectroscopy results. By a systematic study based on STS at ultralow temperature, we observe uniform superconducting gaps on the sample surface. The superconductivity is further confirmed by electrical transport measurements at ultralow temperature, with an onset transition temperature (T_c) up to 1.54 K being observed. The normalized upper critical field h*(T/T_c) behavior and the stability of the superconductivity against the ferromagnet indicate that the discovered superconductivity is unconventional with the p-wave pairing. The systematic STS, and thickness- and angular-dependent transport measurements reveal that the detected superconductivity is quasi-1D and occurs in the surface states. The discovery of the surface superconductivity in TaIrTe₄ provides a new novel platform to explore topological superconductivity and Majorana modes.     

4D spinless topological insulator in a periodic electric circuit

According to the mathematical classification of topological band structures, there exist a number of fascinating topological states in dimensions larger than three with exotic boundary phenomena and interesting topological responses. While these topological states are not accessible in condensed matter systems, recent works have shown that synthetic systems, such as photonic crystals or electric circuits, can realize higher-dimensional band structures. Here, we argue that, because of its symmetry properties, the 4D spinless topological insulator is particularly well suited for implementation in these synthetic systems. We explicitly construct a 2D electric circuit lattice, whose resonance frequency spectrum simulates the 4D spinless topological insulator. We perform detailed numerical calculations of the circuit lattice and show that the resonance frequency spectrum exhibits pairs of 3D Weyl boundary states, a hallmark of the nontrivial topology. These pairs of 3D Weyl states with the same chirality are protected by classical time-reversal symmetry that squares to +1, which is inherent in the proposed circuit lattice. We also discuss how the simulated 4D topological band structure can be observed in experiments.     

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.     

The p-orbital magnetic topological states on a square lattice

Honeycomb or triangular lattices were extensively studied and thought to be proper platforms for realizing the quantum anomalous Hall effect (QAHE), where magnetism is usually caused by d orbitals of transition metals. Here we propose that a square lattice can host three magnetic topological states, including the fully spin-polarized nodal loop semimetal, QAHE and the topologically trivial ferromagnetic semiconductor, in terms of the symmetry and k · p model analyses that are material independent. A phase diagram is presented. We further show that the above three magnetic topological states can indeed be implemented in the two-dimensional (2D) materials ScLiCl₅, LiScZ₅ (Z=Cl, Br) and ScLiBr₅, respectively. The ferromagnetism in these 2D materials is microscopically revealed from p electrons of halogen atoms. This present study opens a door to explore the exotic topological states as well as quantum magnetism from p-orbital electrons by means of the material-independent approach.     

从相对论到规范不变性原理——从剩余结构的观点看外尔和爱因斯坦之争

规范理论的创始人外尔,在1918年运用爱因斯坦建立相对论的思想和方法,把“尺度相对性原理”同“运动相对性原理”相比较,大胆地提出了规范不变性原理,这勇敢的一步在得到了爱因斯坦由衷赞赏的同时,也遭到爱因斯坦的严厉批评,可贵的是外尔自始至终没有放弃自己规范不变性原理的思想。文章使用“剩余结构”理论详细分析了规范理论发展的这关键一步,有利于深刻理解规范不变性原理与数学和物理的关系问题。     

Log-periodic quantum magneto-oscillations and discrete-scale invariance in topological material HfTe5

Discrete-scale invariance (DSI) is a phenomenon featuring intriguing log-periodicity that can be rarely observed in quantum systems. Here, we report the log-periodic quantum oscillations in the longitudinal magnetoresistivity (ρ_xx) and the Hall traces (ρ_yx) of HfTe₅ crystals, which reveal the DSI in the transport-coefficients matrix. The oscillations in ρ_xx and ρ_yx show the consistent logB-periodicity with a phase shift. The finding of the logB oscillations in the Hall resistance supports the physical mechanism as a general quantum effect originating from the resonant scattering. Combined with theoretical simulations, we further clarify the origin of the log-periodic oscillations and the DSI in the topological materials. This work evidences the universality of the DSI in the Dirac materials and provides indispensable information for a full understanding of this novel phenomenon.     

闪锌矿型CdTe电子结构和光学性质的第一性原理

采用基于密度泛函理论(DFT)框架下广义梯度近似平面波超软赝势法,计算了闪锌矿型CdTe的能带结构、态密度和光学性质.计算表明,闪锌矿型CdTe为直接带隙半导体,禁带宽度为0.671eV.计算并分析了闪锌矿型CdTe的复折射率、复介电函数、吸收系数、光电导率、损失函数和反射率,其折射率为2.69,静态介电常数为7.23.计算结果与其他文献结果吻合较好,为闪锌矿型CdTe的应用提供了理论依据.     

分方向教学法在中职体育教学中的应用研究

文章对分方向教学法在中职体育教学中的应用进行研究,总结了中职体育教学的现状及存在的问题,阐述了分方向教学法在中职体育教学中的应用,教育工作者可以通过了解分方向教学的内容,结合学校的实际情况,合理应用这种教学方法,提高体育课堂的教学质量。     

A second look at Egghe’s universal IR surface and a simple derivation of a complete set of universal IR evaluation points

Egghe’s three papers regarding the universal IR surface (2004, 2007, 2008) clearly represent an original and significant contribution to the IR evaluation literature. However, Egghe’s attempt to find a complete set of universal IR evaluation points (P,R,F,M) fell short of his goal: his universal IR surface equation did not suffice in and of itself, and his continuous extension argument was insufficient to find all the remaining points (quadruples). Egghe found only two extra universal IR evaluation points, (1,1,0,0) and (0,0,1,1), but it turns out that a total of 15 additional, valid, universal IR evaluation points exist. The gap first appeared in Egghe’s earliest paper and was carried into subsequent papers. The mathematical method used here for finding the additional universal IR evaluation points involves defining the relevance metrics P,R,F,M in terms of the Swets variables a,b,c,d. Then the maximum possible number of additional quadruples is deduced, and finally, all the invalid quadruples are eliminated so that only the valid, universal IR points remain. Six of these points may be interpreted as being continuous extensions of the universal IR surface, while the other nine points may be interpreted as being “off the universal IR surface.” This completely solves the problem of finding the maximum range possible of universal IR evaluation points.     

高考中少数民族加分政策实施效度的研究—以贵州考生为例

高考少数民族加分政策是针对少数民族考生民族身份的照顾性政策,但由于该政策在实施过程中的效度缺乏分析研究,使得该政策在少数民族增加高等教育机会的获得上作用不明。本文通过对贵州少数民族考生与汉族考生成绩、加分政策效果的对比和分析,得出结论如下:(1)贵州少数民族考生与汉族考生的成绩差距是客观存在的,农村考生中的差距更为明显;(2)少数民族考生在考科的差距上表现出文化选择特性;(3)贵州少数民族加分政策和预科政策对少数民族考生的补偿非常显著。未来的高考改革中,要合理的差别对待城乡少数民族考生间的差距,充分评估涉及高考少数民族的加分政策;考科改革要充分考虑课程的文化属性,即不同考生群体对不同科目的选择性差异。本文还对高考中实现民族间相对公平的努力方向给出了一定基础数据。     

航空装备制造产业专利合作网络结构与演化研究

航空装备制造产业的发展深深影响着我国建设“航空强国”“制造强国” 的成效,分析我国航空装备制造产业专利合作网络结构及演化,有助于航空装备制造产业技术创新能力的提高。以我国航空装备制造产业为研究对象,基于1985—2018年合作申请发明专利数据,运用社会网络分析方法,构建航空装备制造产业专利合作网络,分析我国航空装备制造产业专利合作网络拓扑结构以及网络演化规律。研究发现：我国航空装备制造产业取得快速发展,企业在专利合作网络中占主导地位,但网络整体松散,合作不够紧密,网络的无标度和小世界特性较为明显。从演化规律来看,网络规模持续增长,但密度不断降低,网络节点呈现阶段性变化。