First-principles study of moderate phonon-mediated pairing in high-pressure monoclinic phase of BiS_(2)-based superconductors

Isotope effect on superconductive transition temperature(T_c)is an essential indicator to examine whether the mechanism of superconductors is conventional.Unconventional isotope effect of BiS_(2)-based superconductors has been previously reported in ambient-pressure tetragonal phase.However,to comprehensively ascertain the nature of superconductivity,the investigation of BiS_(2)-based system in high-pressure structure is highly desirable.In this work,we carried out the first-principles calculations of phonon spectra and superconductivity in high-pressure monoclinic phase of LaO_(0.5)F_(0.5)BiS_(2)with ^(32)S and ^(34)S,and observed that the corresponding isotope coefficient is 0.13≤α≤0.20.This value is much greater than that of BiS_(2)-based superconductors in ambient-pressure phase,but slightly smaller than that of conventional MgB_2.Taking into account the calculated T_(c) lower than experimental results,we finally conclude that the moderate phonon-mediated pairing plays a significant role in forming superconductivity of BiS_(2)-based system in high-pressure phase,moreover,the cooperative multiple paring interactions should also be considered.

Explanation of Pressure Effect for High Temperature Superconductors Using Pressure Dependent Schrodinger Equation and String Theory

A pressure dependent Schrodinger equation is used to find the conditions that lead to superconductivity. When no pressure is exerted, the superconductor resistance vanishes beyond a critical temperature related to the repulsive force potential of the electron gass, where one assuming the electron total energy to be thermal, where applying mechanical pressure destroys Sc when it exceeds a certain critical value. However when the electron total energy is an assumed to be that of the free electron model and that the pressure is thermal and mechanical, the situation is different. The quantum expression for resistance shows that the increase of mechanical pressure increases the critical temperature. Such phenomenon is observed in high temperature cupper group.

Combinatorial synthesis and high-throughput characterization of copper-oxide superconductors

Fast synthesis and screening of materials are vital to the advance of materials science and are an essential component of the Materials Genome Initiative. Here we use copper-oxide superconductors as an example to demonstrate the power of integrating combinatorial molecular beam epitaxy synthesis with high-throughput electric transport measurements. Leveraging this method, we have generated a phase diagram with more than 800 compositions in order to unravel the doping dependence of interface superconductivity. In another application of the same method, we have studied the superconductorto-insulator quantum phase transition with unprecedented accuracy in tuning the chemical doping level.

An Experimental Setup for Study of Photoresponse of High T_c Superconductors

We have developed an experimental setup that has been proven suitable for the study of photoresponse of high Tc superconductors. The distinguish feature of this experimental setup lies mainly in the data acquisition system which is equipped with computer as well as the IEEE-488 interface bus. which ensures the accuracy to experimental results. Using the experimental setup, the optical response to laser radiation in high-Tc superconductors has been examined, both of bolometric effect and nonequilibrium optical response are revealed.

The Superconducting Phases in Bi-Sr-Ca-Cu-O and Bi-Pb-Sr-Ca-Cu-O Superconductors at High Temperatures

The addition Of Pb enhances the hightemperature stability as well as theproportion of the high Tphase in Bi-Sr-Ca-Cu-O superconductor.The sample A with nominal composi-tion of BiSrCaCuOwas synthesized bySolid state reaction.It was sintered in airat 1153K for 24h,followed by annealingat 773K for 24h and furnace-cooling.The sample B with a nominal compositionof BiPbSrCaCuOwas prepared bymixing PbO with the powder ofBiSrCaCuOwhich had been prefired at1113K for 24h,pressing,sintering at

CHARACTERISTIC CURVES OF M-H AND COEXISTENCE OF MAGNETISM WITH SUPERCONDUCTIVITY FOR HIGH T_c SUPERCONDUCTORS REBa_2Cu_3OT_(7-x)

Some high T_c superconductors REBa_2Cu_3O_(7-x)(RE=Sm,Eu,Gd,Dy,Ho,Er,Tm) with zero resist- ance temperatures were about 90K have been prepared.The effect of magnetic rare earth ions on the transi- tion temperatures is not very great,but their magnetic behaviours are different from each other.The magnetization loops of these compounds have been measured at 77K.The coexistence of superconductivity with magnetic ordering (COSM) found in the samples with RE=Gd,Dy,Ho,Er,Tm,indicates that there are two possible ways of coexistence in the samples.These expertments show that the relation of paramagnetism to the atomtc number of rare earth elements for these superconductors is similar to that of rare earth ions in some paramagnetic salt crystals,which indicates that the magnetism of the samples origi- nates from the local magnetic moments of rare earth ions.In some samples there is antiferromagnetie ordering at low temperatures,and the effective Bohr magneton numbers are consistent with that of free rare earth ions. Some superconducting parameters including the critical current density are calculated according to Ginzburg-Landau theory and the critical state model.

High-performance diffusion model for inverse design of high Tc superconductors with effective doping and accurate stoichiometry

The pursuit of designing superconductors with high Tc has been a long-standing endeavor.However,the widespread incorporation of doping in high Tc superconductors significantly impacts electronic structure,intricately influencing Tc.The complex interplay between the structural composition and material performance presents a formidable challenge in superconductor design.Based on a novel generative model,diffusion model,and doping adap-tive representation:three-channel matrix,we have designed a high Tc super-conductors inverse design model called Supercon-Diffusion.It has achieved remarkable success in accurately generating chemical formulas for doped high Tc superconductors.Supercon-Diffusion is capable of generating superconduc-tors that exhibit high Tc and excels at identifying the optimal doping ratios that yield the peak Tc.The doping effectiveness(55%)and electrical neutrality(55%)of the generated doped superconductors exceed those of traditional GAN models by more than tenfold.Density of state calculations on the structures further confirm the validity of the generated superconductors.Additionally,we have proposed 200 potential high Tc superconductors that have not been documented yet.This groundbreaking contribution effectively reduces the search space for high Tc superconductors.Moreover,it successfully establishes a bridge between the interrelated aspects of composition,structure,and prop-erty in superconductors,providing a novel solution for designing other doped materials.

超导成“材”之路——实用化高温超导材料的制备及发展

超导材料因具有零电阻效应、完全抗磁性以及量子隧穿效应,在电力、医疗、交通、量子计算、工业、国防等多个领域有着重要的现实意义和巨大的发展前景。自1911年超导现象被发现以来,超导理论、超导材料和超导应用技术均取得了重大进展。近年来,随着制备技术的日益成熟,高温超导材料已经从实验研究走向提升性能、突破应用的实用化阶段。文章将对超导材料的发展历程、物理特性以及分类等进行简要介绍,并系统介绍几种典型的实用化高温超导材料的基本结构、性能特点、制备技术及应用研究进展。在此基础上,对高温超导材料的性能提升和应用发展方向进行展望。

Robust T_c in element molybdenum up to 160 GPa

Element superconductors with the single atoms provide clean and fundamental platforms for studying superconductivity.Although elements with d electrons are usually not favored by conventional BCS,the record superconducting critical temperature(T_(c))in element scandium(S_(c))has further ignited the intensive attention on transition metals.The element molybdenum(M_o)with a half-full d-orbital is studied in our work,which fills the gap in the study of Mo under high pressure and investigates the pressure dependence of superconductivity.In this work,we exhibit a robust superconductivity of Mo in the pressure range of 5 GPa to 160 GPa via high-pressure electrical transport measurements,the T_(c) varies at a rate of0.013 K/GPa to 8.56 K at 160 GPa.Moreover,the superconductivity is evidenced by the T_(c) shifting to lower temperature under applied magnetic fields,and the upper critical magnetic fields are extrapolated by the WHH equation and GL equation;the results indicate that the maximum upper critical magnetic field is estimated to be 8.24 T at 137 GPa.We further investigate the superconducting mechanism of Mo,the theoretical calculations indicate that the superconductivity can be attributed to the strong coupling between the electrons from the partially filled d band and the phonons from the frequency zone of 200-400 cm^(-1).

基于超导的小型化磁粒子成像系统仿真构建

针对磁粒子成像技术尚停留在实验室鼠用设备阶段,传统线材线圈过大,无法在可接受的设备体量内达到临床人体检测所需磁场强度的问题,提出了一种基于超导技术构建高场强、小型化磁粒子成像设备的方法。采用高温超导MgB_(2)线圈替代传统铜线圈,构建磁粒子成像选择场与驱动场。结果表明,在达到相同磁通量的情况下,超导磁粒子成像系统可将两组功能区总质量降低为0.01 kg,设备体积缩小至7 L。在此基础上,采用超导线圈构建梯度磁场还能够获得更高的变化斜率,使零磁扫描区边缘更为清晰规则,移动过程中形态更为稳定,平均直径缩小近二分之一。

基于C++SuperMix库的SIS混频器的研究

基于C++SuperMix软件库对680 GHz接收机中的双槽双超导隧道结(SIS)混频器进行深入模拟研究.在环境温度为4.2 K、本地振荡器(LO)频率为680 GHz、本振功率为100 nW、中频频率中心为10 GHz和中频匹配阻抗为50Ω的条件下,采用二次谐波的谐波平衡法,在0~500 K热噪声源温度下对SIS混频器的输出噪声温度进行建模仿真研究.计算得出:当偏置电压在2~3 mV变化时,SIS混频器的输出噪声温度均小于50 K,表明所研究的SIS混频器具有较好的噪声性能.

高温超导薄膜与超导机理研究

高温超导体的晶格结构通常呈现出层状特征,因此具有低维属性的外延薄膜与异质结构成为了探索高温超导机理的关键材料平台。近年来,原子级精准的外延生长技术更促进了新型超导体的发现。文章将按照超导体系维度下降的脉络,简要介绍高温超导薄膜和异质结构研究对深入理解超导机理的独特贡献。

高压极端条件下的富氢高温超导体

自从在汞中发现4.2 K的超导转变温度以来,寻找室温超导体一直是凝聚态物理领域的研究热点。近年来,科学家在高压极端条件下发现了以共价型H_(3)S(T_(c)=203 K)和离子型LaH_(10)(T_(c)=250 K)、CaH_(6)(T_(c)=215 K)为代表的系列高温超导体,先后刷新了超导转变温度纪录,这些工作开启了学界在富氢化合物中寻找室温超导体的新篇章。本文重点介绍了目前高压下二元和三元富氢高温超导体的理论模拟以及实验制备和表征方面的相关研究进展,分析在富氢化合物中发现室温超导体面临的挑战和可能途径,为实现室温超导做出基础性贡献。

共振非弹性X射线散射在量子材料领域的应用

共振非弹性X射线散射(resonant inelastic X-ray scattering,RIXS)是一种先进的基于同步辐射和自由电子激光光源的光进光出的谱学探测手段.在过去的十几年,RIXS的能量分辨不断被提高,其对凝聚态物质的研究也从最初的晶体场分裂和电荷转移激发,发展到产生于包括电荷、自旋、轨道、晶格4个量子自由度的集体激发行为及相关的序参量.本文总结了近几年高分辨软X射线RIXS在量子材料领域,如铜基和镍基高温超导材料等离子激发及磁激发的研究,量子材料中的集体轨道激发、激子激发和高阶磁激发,以及对磁性金属和拓扑磁性材料中磁激发的探测.

中国高温超导领航人赵忠贤

赵忠贤是中国高温超导研究的重要推动者和践行者。他从1976年开始在国内推动和开展高温超导研究,取得了发现液氮温区铜氧化物超导体和超导临界转变温度在50K以上铁基超导体等重要创新成果。他两度荣获国家自然科学奖一等奖,2017年又获得国家最高科学技术奖。通过对赵忠贤个人经历的考察,发现他在科研上能够不断取得突破与其敏锐的物理直觉、前沿的学科训练以及优秀的科研组织能力息息相关。基于赵忠贤的科研特点,提出了“科学领航人”的概念,并探讨了特征。

Design consideration of a super-high speed high temperature superconductor maglev evacuated tube transport (I)

The super-high speed high temperature superconductor （HTS） maglev evacuated tube transport （ETT） is a promising transport mode for the future. As a key component of the HTS maglev vehicle, the permanent magnet guide- ways （PMGs） with different geometrical configurations and iron yoke widths are analyzed by finite element method （FEM）. The levitation force of a single onboard HTS maglev device over the designed PMG at different field cooling heights （FCH） is measured by magnetic levitation measurement system. Based on the designed PMG and experimental results, a preliminary scheme of subterranean super-high speed HTS maglev ETT is described in this paper. The HTS maglev ETT is mainly composed of an evacuated tube, HTS maglev vehicle, PMG, propulsion system, station, emergency rescue system, etc. In addition, a subterranean tube that consists of foundation tube and vacuum airproof layer is introduced. In order to convert the stress caused by the air pressure difference between inside and outside of the vehicle, a multi-circular vehicle body is designed. The vehicle is driven by a linear motor propulsion system under the control of a ground controlling system. The scheme of long-distance super-high speed passenger transportation is accomplished by the connection of different vehicles.

Nonlocal Theory of High-Temperature Superconductivity

The Boltzmann local physical kinetics forecasts the destruction of SC regime because of the heat movement of particles. Then, the most fundamental distinction between a strange metal and a conventional metal is the absence of well-defined quasi-particles. Here, we show that the mentioned “quasi-particles” are solitons, which are formed as a result of self-organization of ionized matter. Shortcomings of the Boltzmann physical kinetics consist in the local description of the transport processes on the level of infinitely small physical volumes as elements of diagnostics. The non-local physics leads to the theory superconductivity including the high temperature diapason. The generalized non-local non-stationary London’s formula is derived.