CO_2、NH_3对YBa_2Cu_3O_(7-x)的结构及超导电性的影响

以热重分析(TGA)、电阻测量和X射线衍射分析等方法,研究了CO_2与NH_3对YBa_2Cu_3O_(7-x)超导体结构稳定性及超导,电性的影响。当温度低于373K时,CO_2对YBa_2Cu_3O(7-x)的结构和超导电性无影响;当温度为523K时,CO_2使YBa_2Cu_3O_(7-x)的Tc下降;温度高于703K时,CO_2将很快破坏YBa_2Cu_3O_(7-x)的结构,并产生化学反应,生成新的化合物,在CO_2中存在的O_2与N_2对YBa_2Cu_3O(7-x)与CO_2的反应及反应产物的影响有较大差异。NH_3对YBa_2Cu_3O(7-x)结构稳定性的影响不大。     

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.     

N（O）的分布与原子核外电子分布的探讨

本文从超导电性起源于电声子机制出发,讨论了N（O）与原子核外电子层分布及电子层上的电子数的分布之间的关联问题,并用电负性均衡原理讨论了超导材料之中由于元素之间有化学键的形成,元素之间电子发生转移对N（O）的分布影响。     

Topological quantum states of matter in iron-based superconductors: from concept to material realization

We review recent progress in the exploration of topological quantum states of matter in iron-based superconductors. In particular, we focus on the non-trivial topology existing in the band structures and superconducting states of iron’s 3d orbitals. The basic concepts, models, materials and experimental results are reviewed. The natural integration between topology and high-temperature superconductivity in iron-based superconductors provides great opportunities to study topological superconductivity and Majorana modes at high temperature.     

A note on growth of superconductivity patents with two new indicators

Patent statistics may be indicative of growth and evolution of technologies in relation to a scientific field or sub-field of research. In this paper annual growth of patents in the field of superconductivity has been studied. The data in five-yearly cumulation have been set against research papers on superconductivity to show comparative growth of basic research and technological development. Two simple indicators have been devised to understand the apparent influence of basic research on technology and trends of relative growth.     

Superconductivity: technology at zero degrees

Almost 75 years after its discovery, interest in superconductivity is experiencing a revival. For a long time, the properties of metals at extremely low temperatures were a source of fascination mainly to solid-state physicists. Now, however, industry, too, has become interested. In numerous fields, intensive work is going on into commercial applications: from nuclear fusion research to power stations, from hospitals to computer centres. This article looks at both the past and the prospects for the future.     

原创性、引领性科技攻关的历史经验——以国家超导攻关为例

加强原创性、引领性科技攻关是强化国家战略科技力量、实现科技自立自强的关键。1987年开始的国家超导研究开发攻关项目属于引领性、原创性的科技攻关,帮助中国的高温超导研究完成了从落后、跟跑到并跑甚至领跑的跨越,但是并未产生"从0到1"的原始创新。国家超导攻关的历史经验对于原创性、引领性科技攻关有重要启示:(1)基础研究要分类精准施策,区分原始创新与应用牵引、突破瓶颈的基础研究;(2)加快培育战略科学家,充分发挥他们在联结政府与科学共同体之间的枢纽作用;(3)加强国家创新平台建设,将部分集中攻关转化为对战略科技力量的长期支持。     

Superconductivity in chromium nitrides Pr3Cr10-xN11 with strong electron correlations

Exploration of superconductivity in Cr-based compounds has attracted considerable interest because only a few Cr-based superconductors (CrAs, A₂Cr₃As₃ and ACr₃As₃ (A = K, Rb, Cs, Na)) have been discovered so far and they show an unconventional pairing mechanism. We report the discovery of bulk superconductivity at 5.25 K in chromium nitride in Pr₃Cr_10-xN₁₁ with a cubic lattice structure. A relatively large upper critical field of H_c2(0) ∼ 12.6 T is determined, which is larger than the estimated Pauli-paramagnetic pair-breaking magnetic field. The material has a large electronic specific-heat coefficient of 170 mJ K⁻² mol⁻¹—about 10 times larger than that estimated by the electronic structure calculation, which suggests that correlations between 3d electrons are very strong in Pr₃Cr_10-xN₁₁, and thus quantum fluctuations might be involved. Electronic structure calculations show that the density of states at the Fermi energy are contributed predominantly by Cr 3d electrons, implying that the superconductivity results mainly from the condensation of Cr 3d electrons. Pr₃Cr_10-xN₁₁ represents a rare example of possible unconventional superconductivity emerging in a 3D system with strong electron correlations. Nevertheless, clarification of the specific pairing symmetry needs more investigation.     

Edge superconductivity in multilayer WTe2 Josephson junction

WTe₂, as a type-II Weyl semimetal, has 2D Fermi arcs on the (001) surface in the bulk and 1D helical edge states in its monolayer. These features have recently attracted wide attention in condensed matter physics. However, in the intermediate regime between the bulk and monolayer, the edge states have not been resolved owing to its closed band gap which makes the bulk states dominant. Here, we report the signatures of the edge superconductivity by superconducting quantum interference measurements in multilayer WTe₂ Josephson junctions and we directly map the localized supercurrent. In thick WTe₂ (, the supercurrent is uniformly distributed by bulk states with symmetric Josephson effect (). In thin WTe₂ (10 nm), however, the supercurrent becomes confined to the edge and its width reaches up to and exhibits non-symmetric behavior . The ability to tune the edge domination by changing thickness and the edge superconductivity establishes WTe₂ as a promising topological system with exotic quantum phases and a rich physics.     

Stoichiometric evolutions of PH3 under high pressure: implication for high-Tc superconducting hydrides

The superconductivity of hydrides under high pressure has attracted a great deal of attention since the recent observation of the superconducting transition at 203 K in strongly compressed H₂S. It has been realized that the stoichiometry of hydrides might change under high pressure, which is crucial in understanding the superconducting mechanism. In this study, PH₃ was studied to understand its superconducting transition and stoichiometry under high pressure using Raman, IR and X-ray diffraction measurements, as well as theoretical calculations. PH₃ is stable below 11.7 GPa and then it starts to dehydrogenate through two dimerization processes at room temperature and pressures up to 25 GPa. Two resulting phosphorus hydrides, P₂H₄ and P₄H₆, were verified experimentally and can be recovered to ambient pressure. Under further compression above 35 GPa, the P₄H₆ directly decomposed into elemental phosphorus. Low temperature can greatly hinder polymerization/decomposition under high pressure and retains P₄H₆ up to at least 205 GPa. The superconductivity transition temperature of P₄H₆ is predicted to be 67 K at 200 GPa, which agrees with the reported result, suggesting that it might be responsible for superconductivity at higher pressures. Our results clearly show that P₂H₄ and P₄H₆ are the only stable P–H compounds between PH₃ and elemental phosphorus, which is helpful for shedding light on the superconducting mechanism.     

High-Tc superconductor Fe(Se,Te) monolayer: an intrinsic,scalable and electrically tunable Majorana platform

Iron-based superconductors have been identified as a novel platform for realizing Majorana zero modes (MZMs) without heterostructures, due to their intrinsic topological properties and high-T_c superconductivity. In the two-dimensional limit, the FeTe_1−xSe_x monolayer, a topological band inversion has recently been experimentally observed. Here, we propose to create MZMs by applying an in-plane magnetic field to the FeTe_1−xSe_x monolayer and tuning the local chemical potential via electric gating. Owing to the anisotropic magnetic couplings on edges, an in-plane magnetic field drives the system into an intrinsic high-order topological superconductor phase with Majorana corner modes. Furthermore, MZMs can occur at the domain wall of chemical potentials at either one edge or certain type of tri-junction in the two-dimensional bulk. Our study not only reveals the FeTe_1−xSe_x monolayer as a promising Majorana platform with scalability and electrical tunability and within reach of contemporary experimental capability, but also provides a general principle to search for realistic realization of high-order topological superconductivity.     

Iron-based high transition temperature superconductors

In a superconductor electrons form pairs and electric transport becomes dissipation-less at low temperatures. Recently discovered iron-based superconductors have the highest superconducting transition temperature next to copper oxides. In this article, we review material aspects and physical properties of iron-based superconductors. We discuss the dependence of transition temperature on the crystal structure,the interplay between antiferromagnetism and superconductivity by examining neutron scatering experiments, and the electronic properties of these compounds obtained by angle-resolved photoemission spectroscopy in link with some results from scanning tunneling microscopy/spectroscopy measurements.Possible microscopic model for this class of compounds is discussed from a strong coupling point of view.     

Double-frequency Aharonov-Bohm effect and non-Abelian braiding properties of Jackiw-Rebbi zero-mode

Ever since its first proposal in 1976, Jackiw-Rebbi zero-mode has been drawing extensive attention for its charming properties including charge fractionalization, topologically protected zero-energy and possible non-Abelian statistics. We investigate these properties through the Jackiw-Rebbi zero-modes in quantum spin Hall insulators. Though charge fractionalization is not manifested, Jackiw-Rebbi zero-mode''s zero-energy nature leads to a double-frequency Aharonov-Bohm effect, implying that it can be viewed as a special case of Majorana zero-mode without particle-hole symmetry. Such relation is strengthened for Jackiw-Rebbi zero-modes also exhibiting non-Abelian properties in the absence of superconductivity. Furthermore, in the condition that the degeneracy of Jackiw-Rebbi zero-modes is lifted, we demonstrate a novel non-Abelian braiding with continuously tunable fusion rule, which is a generalization of Majorana zero-modes’ braiding properties.     

科学史视域下的原始创新:以高温超导研究为例

原始创新是国际科技竞争的制高点。目前我国高度重视培育原始创新,但学术界对于原始创新的内在特征缺乏研究。高温超导研究是当代科学史的典型案例。通过梳理关键时间节点和重大科学事件完成了高温超导知识史的建构,以此界定原始创新、一阶创新、二阶创新的概念、特征和内涵。高温超导的发现改变了超导领域的整体格局和研究面貌,具有颠覆性的范式革新意义,是“从0到1”的原始创新。一阶创新有两种类型：一是具有一定的颠覆性,但程度不如原始创新,未能建立新的范式;二是在新范式建立之前大力推动常规科学的进步。二阶创新是跟踪性、扩展性的研究所取得的重要创新成果。用科学史的方法分析创新的内在特征,判断创新的性质,是一条可行的路径。     

Direct observation of nodeless superconductivity and phonon modes in electron-doped copper oxide Sr1−xNdxCuO2

The microscopic understanding of high-temperature superconductivity in cuprates has been hindered by the apparent complexity of crystal structures in these materials. We used scanning tunneling microscopy and spectroscopy to study the electron-doped copper oxide compound Sr_1−xNd_xCuO₂, which has only bare cations separating the CuO₂ planes and thus the simplest infinite-layer structure of all cuprate superconductors. Tunneling conductance spectra of the major CuO₂ planes in the superconducting state revealed direct evidence for a nodeless pairing gap, regardless of variation of its magnitude with the local doping of trivalent neodymium. Furthermore, three distinct bosonic modes are observed as multiple peak-dip-hump features outside the superconducting gaps and their respective energies depend little on the spatially varying gaps. As well as the bosonic modes, with energies identical to those of the external, bending and stretching phonons of copper oxides, our findings reveal the origin of the bosonic modes in lattice vibrations rather than spin excitations.     

Six-membered-ring inorganic materials: definition and prospects

The six-membered ring (SMR) is a common structure unit for numerous material systems. These materials include, but are not limited to, the typical two-dimensional materials such as graphene, h-BN, and transition metal dichalcogenides, as well as three-dimensional materials such as beryllium, magnesium, MgB₂ and Bi₂Se₃. Although many of these materials have already become ‘stars’ in materials science and condensed-matter physics, little attention has been paid to the roles of the SMR unit across a wide range of compositions and structures. In this article, we systematically analyze these materials with respect to their very basic SMR structural unit, which has been found to play a deterministic role in the occurrence of many intriguing properties and phenomena, such as Dirac electronic and phononic spectra, superconductivity and topology. As a result, we have defined this group of materials as SMR inorganic materials, opening up a new perspective on materials research and development. With their unique properties, SMR materials deserve wide attention and in-depth investigation from materials design, new physical discoveries to target-wizard applications. It is expected that SMR materials will find niche applications in next-generation information technology, renewable energy, space, etc.     

High temperature superconductivity research in the USSR

The rapid developments in high temperature superconductivity research in recent years have confronted the USSR with its first real test of restructuring (perestroika) in science. The breakthrough in this field in 1986–1987 posed a number of major problems for the traditional Soviet system in science. In particular the field required the cooperation of scientists from different fields and the ability to respond rapidly to the new developments. Soviet science has not been noted for its rapid response in its planning, its supply system and its information and publication procedures. In addition, the investigation of the new substances required modern sophisticated equipment, the provision of which has been a particular weakness of Soviet science.Academician Osip'yan saw the new field as a key test of perestroika in science and largely as a result of his influence it was used as a test-bed for new ideas for the organisation of science. It became the first of a new series of major programmes in which funds were allocated to groups of scientists on a competitive basis and the groups themselves, rather than their organisations, controlled the use of these funds. Despite some success in keeping up with world developments the programme has been hampered by bureaucracy and the lack of modern equipment.The study highlights the changes which have occurred in Soviet science under Gorbachev and shows that many aspects of the traditional system still remain.     

Identification of twist-angle-dependent excitons in WS2/WSe2 heterobilayersOA

Stacking atomically thin films enables artificial construction of van der Waals heterostructures with exotic functionalities such as superconductivity, the quantum Hall effect, and engineered light-matter interactions.In particular, heterobilayers composed of monolayer transition metal dichalcogenides have attracted significant interest due to their controllable interlayer coupling and trapped valley excitons in moiré superlattices. However, the identification of twist-angle-modulated optical tr...     

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.     

三叶青藤特性及苗木繁育技术研究

在3、5、7、9、11月五个月份采集三叶青藤二年生茎藤,分别用北京产双吉尔GGK6号生根粉50mg．kg-1浸泡2小时进行扦插试验;用随采随播、5天后播种、10天后播种、15天后播种、20天后播种五种方法进行种子发芽试验。结果表明,扦插育苗试验时五个月份的生根率分别是79．2％、82．8％、69．6％、62．4％、44％;种子育苗时五种处理的发芽率分别是96％、79％、57％、20％、11％。5月份扦插育苗效果最好,生根率达到82．8％;播种育苗时随采随播的效果最好,发芽率达到96％;在生产上采用扦插育苗会有更多的优势。