Applied High-Tc Superconducting Electrical Machines

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科技词汇

（科技<汉译英>）播客video blog on the Internet首航maiden voyage网恋online love affair遥感remote sensing导航栏navigation bar智能卡smart card信息港info port月球车lunar rover背投屏幕rear projection screen边缘科学boundary science电信业务the telecommunication sector感知技术perceptive technology观测装置stereo camera光纤通信optical fiber communication火炬计划Torch Program机器语言machine language基因工程genetic/gene engineering技术产权technology property rights技术更新technological upgrading尖端技术state –of-the-art technology科技含量scientific and technological content 可视图文visual pictures and literature克隆技术cloning technology空间探测space exploration蓝牙技术Bluetooth technology立体农业stereo farming模拟技术analog technology偏离轨道veer off course气象卫星meteorological satellite前瞻技术foresight technology清晰影像 a full high-resolution picture燃料电池fuel cell人机交互human-computer interaction认证授权certificate authority实时处理real-time processing试管婴儿test-tube baby手动搜索manual search数字机遇digital opportunities双星计划Double Star Program通信卫星communication satellite同步卫星geostationary satellite网格计算grid computing网络课堂online class网络数据network database网络诈骗cyber fraud网上冲浪surf the Internet网上购物online shopping网上聊天online chatting网上通信online navigation卫星导航satellite navigation无人飞船unmanned spaceship无土栽培soilless cultivation无性繁殖asexual reproduction新能源观new thinking on energy development信息高地information highland移动计算mobile computing载人航天Manned Space Flight自主计算autonomic computing字符识别character recognition网络综合症net synthesis国际空间站International Space Station技工贸结合integrate scientific and technological developmentwith industrial and trade development蛋白质工程protein engineering模拟计算机analog computer数字化战场digitize the battlefield数字显示器digital display硬盘驱动器hard-disk drive无线寻呼网radio paging network转基因动物genetically modified animal (GMA)转基因食品genetically modified food (GMF)智能终端机intelligent terminal产品科技含量technological element of a product大容量高速率high-capacity and high-speed电子商务认证E-business certification多任务小卫星small multi-mission satellite (SMMS)国防关键技术defense critical technology基础传输网络basic transmission network技术合作活动technological cooperation process高温超导电缆high-TC superconducting cable空间物理探测space physics exploration交互信息网络interactive information network科教兴国战略the strategy of revitalizing China through science and education太阳能电池板solar panel数字图像处理digital image processing密钥加密技术Key Encryption Technology网上交易平台online trading platform消除数字鸿沟bridge the digital divide信息基础设施information infrastructure虚拟现实技术virtual reality technology月球探测卫星lunar probe推广科技成果turn laboratory achievements intocommercial/mass production无线电导航设备radio navigation device先进的安全技术leading-edge security technologies新兴高科技产业new high-tech industries国家重点实验室national key laboratory加快信息化进程accelerate the informationization process宽带高速信息网high-speed broadband information networks重组DNA技术recombinant DNA technology全球电子商业框架 a framework for global E-commerce信息的选择性传播selective dissemination of information信息社会协调发展coordinated development of information society信息通讯管制体系infocom regulation system改善社会信息服务render better information services to society空间环境探测系统space environment detector system知识创新工程试点pilot knowledge innovation project科学技术教育与培训S&T education and training前沿性、交叉性研究pioneering and interdisciplinary research以信息化带动工业化industrialization through informationization月球的重力场和环境gravity field and environment of the moon有机（生化）纳米材料organic nanomaterial中国已成功地发射了第一颗实验通讯卫星。

毕业设计课题(论文)任务书

毕业设计课题（论文）任务书系部：计量工程系专业：供用电技术专业班级供电08—1指导老师（含职称）：刘海客课题（论文）题目：配电系统中分布式电源的接入一：设计（论文）的主要任务及目的供用电技术专业毕业设计是实现本专业人才培养目标要求的重要阶段。

通过本课题的毕业设计，学生将加深、巩固对供电、用电相关基础知识的理解，并学会利用所学专业基础知识解决供电、用电相关岗位的工作上遇到的实际问题。

本课题要求基于配电系统中分布式电源的接入分析设计，其目的和任务是：（1）巩固《电力系统分析》的相关基础知识，锻炼学生进行电力系统分析的能力；（2）巩固《供用电设备》所学知识，锻炼学生进行组合各种供用电设备的实践能力；（3）巩固《供用电网络继电保护》，锻炼学生根据元件参数设计继电保护的能力；（4）巩固所学的电气主接线知识和绘图知识，锻炼学生应用电气CAD等软件绘制工厂变电所计算用电气主接线简图的能力；通过本次毕业设计，要求学生进一步加深对基础理论的理解，扩大专业知识面，完成教学计划规定的基本理论、基本方法和基本技能的综合训练，力求在收集资料、查阅文献、调查研究、方案制定、计算机处理、撰写论证、口述表达等方面加强训练，实现所学知识向能力的转化。

同时培养学生严肃认真的科学态度，求实的工作作风和良好的协作精神、创新意识。

毕业设计应充分体现“教师指导下得以学生为中心”的教学模式，以学生为认知主题，充分调动学生的积极性和能动性，重视学生自学能力和自组织能力的培养。

要求学生按时完成论文写作任务，灵活运用资料，切记不可抄袭。

二：设计（论文）的基本内容：1．设计资料1. PU TTGEN H B , MACGREGOR P R , LAMBERT F C. Distributed generation : semantic hype or the dawn of a new era IEEE Power and Energy Magazine , 2003 , 1 (1) : 22-29.2. 王成山，王守相．分布式发电供能系统若干问题研究．电力系统自动化，2008，32（20）：1-4,31．Wang Chengshan, Wang Shouxiang．Study on Some Key Problems Related toDistributed Generation Systems．Automation of Electric Power Systems, 2008,32(20):1-4,31．3. 李天友，金文龙，徐丙垠．“配电技术”．中国电力出版社，北京，2008年3月．Li Tianyou, Jin Wenlong, Xu Bingyin．“Distribution Technology”，ChinaElectric Power Press, Beijing, March,2008．4. 梁有伟, 胡志坚, 陈允平. 分布式发电及其在电力系统中的应用综述. 电网技术, 2003, 27 (12):71-75,88.Liang Youwei, Hu Zhijian, Chen Yunping. A Survey of Distributed Generation and Its Application in Power System. Power System Technology, 2003, 27(12):71-75,88.5. 严俊，赵立飞. 储能技术在分布式发电中的应用. 华北电力技术，2006，第10期，16-19.Yan Jun, Zhao Lifei. Energy Storage for Distributed Generation. North China Electric Power, 2006, No.10, 16-19.Deng Zigang, Wang Jiasu, Wang Suyu etc..Status of High Tc superconducting Flywheel Energy Storage System. Transactions of China Electrotechnical Society, 2008, 23(12):1-10.6. 胡学浩．分布式发电（电源）技术及其并网问题．电工技术杂志，2004，第10期, 1-5. Hu Xuehao. Distributed Generation and Grid-connected Technology. Electric Engineering,2004, No.10, 1-5.7. 鲁宗相‘王彩霞‘阂勇‘周双喜‘, 吕金祥, 王云波，微电网研究综述，电力系统自动化，2007，31（19）：100-107.Lu zhongxiang. Wang Caixia. Min Yong. Zhou Shuangxi. Lu Jinxiang, Wang Yunbo, Overview on Micro Grid Research, Automation of Electric Power Systems, 2007,31(19):100-1078. Christian Schulz. Gerold R?der. Michel Kerrat, Virtual Power Plant With Combined Heat and Power Micro-units, CIRED Seminar 2008: SamrtGrids for Distribution,June,2008,Frankfut参考网站国农村电气化信息网、输配电设备网、北极星电力网、国家电力信息网、中国电力新闻网2．设计内容（1）分布式电源概述1.1分布式电源的概念1.2 分布式电源系统结构1.3 分布式电源的技术特点（2）分布式电源的发展现状2.1国外分布式电源发展2.2 国内分布式电源发展（3）分布式电源接入对电网的影响3.1对电网规划的影响3.2对线路上潮流的影响3.3对网损的影响3.4对电能质量的影响3.5对系统保护的影响3.6对可靠性的影响3.7非正常孤岛问题3.8其他方面的问题（4）分布式电源接入电网的环境和条件（5）分布式电源的相关国家标准5.1分布式电源接入配电网的技术规定5.2分布式电源接入配电网的测试规定5.3分布式电源接入配电网的运行控制规范5.4分布式电源接入配电网的监控系统功能规范（6）分布式电源并网关键技术6.1国外经验6.2分布式智能发电技术6.3分布式电源信息交互技术6.4分布式电源规划设计技术6.5适用于分布式电源新型储能技术6.6分布式电源并网运行调度技术6.7分布式电源标准体系和检测技术（7）分布式电源技术展望（8）总结3．基本要求1、论文应做到中心突出，层次清楚，结构合理；必须观点正确，论据充分，条理清楚，文字通顺；并能进行深入分析，见解独到。

美联英语：高科技类新词汇汇总

美联英语提供：美联英语：高科技类新词汇汇总小编给你一个美联英语官方试听课申请链接：/?tid=16-73374-0 3C 融合（3c fusion）3G（3rd Generation）3R技术（3R techniques）4A（Anyone Anytime Anywhere Anything）CG（Computer Graphics ）DVD（Digital Versatile Disk，多功能数码光盘）EVD （Enhanced Versatile Disk，增强型多媒体盘片系统）Open AccessSOI材料（Silicon on Insulator Materials）Wi－Fi技术（Wireless Fidelity）阿尔法客车”（AlphaBus）爱普（APIEL：Advanced Placement International English Language）按需计算（On－Demand Computing）白色农业（white agriculture）办公自动化（OA：Office Automation）半导体材料（semiconductor material）比较医学（Comparative Medicine）并行工程（Concurrent Engineering）博客（Blog/Blogger）超级网站（Super Website）城市垃圾管理的三C原则（Clean Cycle Control）创新决策权（Authority innovation－decisions）磁悬浮列车（Magnetically Levitated Train）大规模杀伤性武器（Weapons of mass destruction）（陶子）中微子（Tau neutrino ）大科学（Big Science）地球模拟器（Earth Simulator）地球资料卫星（earth resources satellite）地震矩规模（moment magnitude scale）电子现金（Electronic Cash）电子支票（Electronic Check）动漫（Comic and Animation）都市农业（Urban Agriculture或Agriculture in City Countryside）二恶英”（Dioxin）非典型肺炎（Atypical Pneumonias）分布式计算（Distributed Computing）分布式能源（distributed energy sources）分子遗传学（Molecular genetics）疯牛病（Mad Cow Disease）干扰素（Interferon）干细胞（Stem Cells）干燥综合征（Sjogren Syndrome，SS）高技术（High T echnology，简称Hi－tech）高技术战争（high－tech warfare）高温超导电缆（High－TC Superconducting Cable）高温超导体（High－TC Superconductor）公共密钥基础结构（Public Key Infrastructure，PKI）供应链管理（Supply Chain Management）光纤通信（Optical Fiber Communication）国防高技术（defense high technology）国防关键技术（defense critical technology）国防信息基础结构（DII Defence Information Infrastructure）国际空间站（ISS（International Space Station）互联网时间（Internet Time）机顶盒（Set－Top Box，简称STB）基础研究（Basic Research）基因歧视（Gene Discrimination）基因枪法（particle bombardment）基因疫苗（Gene Vaccine）基因诊断（Gene Diagnosis）基因指纹法（Genetic Fingerprint）基因治疗（Gene Therapy）极端制造（Extreme manufacturing）集束炸弹（Cluster bombs）技术推广与科技服务季节失调症（maladjustment in season）建筑设备自动化系统（Building Automation System，简称BAS）健康住宅（Healthy Building or Healthy House）降水概率（precipitation probability）降水量（rainfall precipitation）金属玻璃（Metallic Glasses）京都议定书（Kyoto Protocol）精确农业（Precision Agriculture）精神领袖（Spiritual leader ）精准农业（Precision Agriculture）巨磁电阻材料（Giant Magnetoresistance Materials）聚合酶链反应（Polymerase Chain Reaction ，PCR）军事革命（revolution in military affairs）科学技术教育与培训（S&T education and training）科学素养（Scientific Literacy）可视图文（Visual pictures and literature）空间站（space station）空中交通管制（air traffic control―ATC）蓝色农业（blue agriculture）蓝牙技术（Bluetooth）立体农业（stereo farming）量子纠缠（Quantum Entanglement）量子密码术（Quantum cryptography）量子隐形传送（Quantum Teleportation）硫污染（Pollution by Sulfur）绿色GDP（Green GDP）绿色纤维（Lyocell fibre）绿箱政策（GreenBox Policies）密钥加密技术（Key Encryption T echnology）敏捷制造（Agile Manufacturing）（20030731）纳米材料（nano material）与纳米粒子（nano particle）纳米机器人（Nano Robot）纳米科学技术（NanoST （Nano Science and Technology））纳卫星（Nano－Satellite）农业产业化（Agriculture Industrialization）欧洲洁净空气”计划（CAFE （Clean “Air For Europe rogramme”）贫铀弹（Depleted Uranium Bomb）平均无故障工作时间（mean－time－between－failures ―MTBF）普适计算（Pervasive Computing）气象卫星（meteorological satellite）千年生态系统评估（Millennium Ecosystem Assessment）清洁生产（Cleaner Production）全球定位系统（Global Positioning System，简称GPS）全球警报与反应网络（Global Out－break Alert and Response Network）燃料电池（Fuel Cell）人工乘客（Artificial Passenger）人类脑计划（Human Brain Project）人文发展指数（HDI）认证中心（Certificate Authority，简称CA）柔性制造技术（flexible manufacturing technology―FMT）朊毒体（Prion）深空探测（Deep Space Exploration）生命体征（vital signs）生命体征（vital signs）生态预报（ecological forecasting 或ecological）生物安全（Biosafety）生物防治（biological control）生物经济（Bio－economy）生物库”计划（“Biobank”Project ）生物入侵（Biological invasion）生物芯片（Biochip）生物信息学（Bioinformatics）生物质能（Biomass Energy）时间旅行（Time Travel）试验发展（Development）受众分割（Audience segmentation）数字地球（Digital Earth ）数字地球（Digital Earth）数字电视（Digital TV，简称DTV）数字鸿沟（Digital Divide）数字化战场（digitizing the battlefield ―DB）数字视频广播（DVB “Digital Video Broadcast”）数字图书馆（DL “Digital Library”）数字显示器（Digital Display）数字现金（Digital Cash）数字音频磁带（DAT “Digital Audio Tape”）数字自然音影技术（DNA “Digital Natural Audio/Video”）双星计划（Double Star Programme）水资源（Water Resources）酸雨（Acid Rain）外科手术式打击（Surgical strike）网格计算（Grid Computing）网络数据库（Network Database）网络综合症（Net Synthesis）危机管理（Crisis Management）微机电系统（Micro Electro－Mechanical Systems，MEMS）微流体技术（Microfluidics Technology）温室效应（Greenhouse Effect）物理农业（Physical Agriculture严重急性呼吸道综合症（SARS：Severe Acute Respiratory Syndrome）阳光政策（Sunshine policy）遥感（Remote Sensing）遥医学（Telemedicine）液晶（Liquid Crystal）液晶（liquid crystal）液晶显示器（Liquid Crystal Display，LCD）一票否决权（veto power）医学遗传学（medical genetics）医院信息系统（Integrated Hospital Information System，IHIS）移动计算（Mobile Computing）移动上网（WAP）遗传筛查（Genetic Screening）应用研究（Application Research）营养免疫（Nutrition Immunology）有机（生化）纳米材料（Organic （Biochemical）Nanomaterial）预发式计算（Proactive Computing）远程呈现（telepresence）远程医学（Telemedicine）载人航天（Manned Space Flight）载人航天（manned spaceflight）摘菊使者（Daisy Cutter）知识管理（Knowledge Management，简称KM）知识经济（The Knowledge Economy）知识引擎（Kengine）知识与资源管理（KRM：Konwlege & Resource Management）脂质体（Liposome）植物全息现象（Plant Holographic Images）中国强制认证（CCC“China Compulsory Certification”）重组DNA技术（Recombinant DNA Technology）转基因动物（Genetically Modified Animal）转基因食品（Genetically Modified Food）准晶（Quasicrystal）准一维纳米材料（Quasi－one－dimensional Nanometer Material）资源安全（Resource Security）自主计算（Autonomic Computing）综合性安全（Comprehensive Security，或非传统安全）总部经济（Headquarters Economy）组织培养技术（Tissue Culture Technology）太空农业（Space Agriculture）太空行走（Walking in space）太阳风暴（Solar Storm）太阳能（Solar Energy）炭疽（Anthrax）炭疽（anthrax）唐氏综合症（Downs Syndrome）提高战略运算能力计划Accelerated Strategic Computing Initiative，ASCI 体细胞遗传学（somatic genetics）通信卫星（communication satellite）西尼罗河病毒（West Nile virus）消费电子（consume electronics）信息材料（information materials）信息技术外包（IT Outsourcing）信息经纪人（Information Broker）信息战（information warfare―IW）休闲农业（Recreational Agriculture）虚拟口腔（DentAART）虚拟人（Visual Human）虚拟人（Visual human）虚拟天文台（Virtual Observatory）虚拟现实技术（Virtual Reality Technology）循环经济（Recycling Economy / Cyclic Economy）美联英语：。

准一维超导体K2Mo3As3中超导电性的再现

Reemergence of superconductivityin pressurized quasi-one-dimensional superconductor K2Mo3As3Cheng Huang1,2*, Jing Guo1,4*, Kang Zhao1,2*, Fan Cui1,2, Shengshan Qin1,2, Qingge Mu1, Yazhou Zhou1, Shu Cai1,2, Chongli Yang1, Sijin Long1,2, Ke Yang3, Aiguo Li3,Qi Wu1, Zhian Ren1,2, Jiangping Hu1,2 and Liling Sun1,2,4†1Institute of Physics and Beijing National Laboratory for Condensed Matter Physics,Chinese Academy ofSciences, Beijing 100190, China2University of Chinese Academy of Sciences, Beijing 100190, China3Shanghai Synchrotron Radiation Facilities, Shanghai Institute of Applied Physics, Chinese Academy of Sciences,Shanghai 201204, China4Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China Here we report a pressure-induced reemergence of superconductivity in recently discovered superconductor K2Mo3As3, which is the first experimental case observed in quasi-one-dimensional superconductors. We find that, after full suppression of the ambient-pressure superconducting (SC-I) state at 8.7 GPa, an intermediary non-superconducting state sets in and prevails to the pressure up to 18.2 GPa, however, above this pressure a new superconducting (SC-II) state appears unexpectedly. High pressure x-ray diffraction measurements demonstrate that the pressure-induced dramatic change of the lattice parameter c contributes mainly to the emergence of the SC-II state. Combined with the theioretical calculations on band strcture, our results suggest that the reemergemce of superconductivity is associated with the change of the complicated interplay among different orbital electrons, driven by the pressure-induced unisotropic change of the lattice.The discoveries of the copper oxide and iron-based high-T c unconventional superconductors have generated considerable interest over the past 30 years due to their unusal superconducting mechanism and great potential for application. A common feature of these superconductors is that they contain d orbital electrons in their quasi-two-dimentional lattice that results in intriguing superconductivity and other exotic properties [1-6]. Recently, a family of CrAs-based superconductors with superconducting transition temperatures (T c) of 2.2 - 8.6 K were found in X2Cr3As3 (X=Na, K, Rb, Cs) compounds, which possess the features of containing d orbital electrons in a quasi-one-dimensional lattice [7-10] and many unconventional properties [11]. Soon after, a new family of quasi-one-dimmensional MoAs-based superconductors Y2Mo3As3(Y= K, Rb, Cs) with T c s from 10.4 K to 11.5 K was discovered [12-14]. The properties of the upper critical field and specific-heat coefficient of the Y2Mo3As3 superconductors are similar to those of X2Cr3As3.The crystal structure of the Y2Mo3As3 superconductors is same as that of X2Cr3As3, crystallized in a hegxagonal unit cell without an inversion symmetry [12]. The alkali metallic atoms serve as the charge reservoir and the Mo-As chains are responsible for their superconductivity [12]. Since these superconductors host non-centrosymmetric structure that usually connects to the unconventional pairings and exotic physics, they have received considerable attentions in the field of superconductivity researches [15-19].Pressure tuning is a clean way to provide significant information on evolution among superconductivity, electronic state, and crystal structure without changing the chemical composition, and eventually benefits for a deeper understanding of the underlying physics of the puzzling state emerged from ambient-pressure materials[2,20-24]. Earlier high pressure studies on X2Cr3As3(X=K and Rb) below ~4 GPa found that its superconductivity can be dramatically suppressed by external pressure [25,26], however, high pressure studies on the K2Mo3As3 superconductor is still lacking. In this study, we performed the in-situ high pressure transport measurements on the K2Mo3As3 sample up to 50 GPa to know what is new for this compound under high pressure.The polycrystalline (wire-like) samples, as shown in the inset of Fig. 1a, were synthesized using a conventional solid-state reaction method, as described in Ref. [12]. High pressure was generated by a diamond anvil cell made from a Be-Cu alloy with two opposing anvils. Diamond anvils with 300 culets (flat area of the diamond anvil) were used for the experiments. In the resistance measurements, we used platinum foil as electrodes, rhenium plate as gasket and cubic boron nitride as insulating material. The four-probe method was employed to determined pressure dependence of superconducting transition temperature. In the high-pressure ac susceptibility measurements, the sample was surrounded by a secondary coil (pickup coil), above which a field-generating primary coil was wounded [21, 27]. High-pressure angle dispersive x-ray diffraction (XRD) measurements were carried out at beamline 15U at the Shanghai Synchrotron Radiation Facility. A monochromatic x-ray beam with a wavelength of 0.6199 Å was adopted. The pressure was determined by ruby fluorescence method [28]. Given that the sample reacts with the pressure transmitting mediums under pressure, no pressure medium was adopted in all high-pressure measurements.Figure1a shows the temperature dependence of the electrical resistance of the ambient-pressure sample with an onset T c of about 10.4 K, in good agreement with the previous report [12]. Figure 1b-1d show the high pressure results. It is seen that theresistance at 1.2 GPa shows a remarkable drop starting at ~9.2 K and reaches zero at ~ 4.5 K (inset of Fig. 1b), indicating that the applied pressure decreases the onset T c from 10.4 K to 9.2 K. Upon further increasing pressure to 1.5 GPa, the sample loses its zero resistance and its T c shifts to lower temperature, reflecting that the superconductivity of this polycrystalline sample is highly sensitive to the applied pressure. Then, T c decreases continuously with a rate of d T c/d P= -1.19 K/GPa until cannot be detected at 8.7 GPa down to 1.6 K (Fig. 1b). The non-superconducting state persists to the pressure of 18.2 GPa, at which unexpectedly another remarkable resistance drop is found at ~ 4.6 K (Fig. 1c). This drop becomes more pronounced with further compression (Fig. 1d), and plunges about 92% at 47.4 GPa. Moreover, we find that the onset temperature of the new resistance drop shifts to high temperature with increasing pressure initially (the inset of Fig. 1d), reaches a maximum (~8.1 K) at ~ 30 GPa and saturats up to ~38 GPa. By applying higher pressure to 47.4 GPa, the temperature of the drop displays a slow decline (inset of Fig. 1d).To confirm whether the new resistance drop observed in K2Mo3As3 is related to a superconducting transition, we applied magnetic field to the sample subjected to 19.6 GPa and 41.8 GPa, respectively (Fig. 2a and 2b). It can be seen that this new resistance drop shifts to lower temperature with increasing magnetic field and almost suppressed under the magnetic field of 3.5 T and 4.0 T for the compressed sample at 19.6 GPa and 41.8 GPa, respectively. These results indicate that the new resistance drop should be resulted from a superconducting transition. The alternating-current (ac) susceptibility measurements were also performed for the sample subjected to 20 GPa - 44 GPa down to 1.5 K, the lowest temperature of our instrument, but the diamagnetism is not detected. By our analysis, the failure of the measurements on the diamagnetism may be related to the low volume fraction of the pressure-induced superconducting phase.We extract the field (H) dependence of T c for K2Mo3As3 at 19.6 GPa and 41.8 GPa (Fig. 2a and 2b) and plot the H(T c) in Fig. 2c. The experimental data is fitted by using Ginzburg-Landau (GL) formula, which allows us to estimate the values of the upper critical magnetic field (H C2) at zero temperature: 4.0 T at 19.6 GPa and 4.8 T at 41.8 GPa (Fig. 2c). Note that the upper critical fields obtained at 19.6 GPa and 41.8GPa are lower than their corresponding Pauli paramagnetic limits (10.3 T and 14.8T, respectively), suggesting that the nature of the pressure-induced superconducting state may differ from that of the initial superconducting state.To investigate whether the observed reemergence of superconductivity in pressurized K2Mo3As3 is associated with the pressure-induced crystal structure phase transition, we performed in-situ high pressure XRD measurements. The XRD patterns collected at different pressures are shown in Fig. 3. No structure phase transition is observed under pressure up to 51.6 GPa. And all peaks shift to higher angle due to the shrinkage of the lattice, except for the (002) peak. It is found that the (002) peak, which is realted to the parameter c, shifts toward to the lower angle starting at 8.8 GPa. Upon further compression, it becomes more pronounced. We propose that the left shift of the (002) peak may be a consequence of the pressure-induced elongation of the polycrystalline wire-like samples (the direction of the wire length is the c-axis of the K2Mo3As3 crystal lattice) due to their preferred orientation under pressure (see the right panel of Fig. 3). At higher pressure, the wire-like samples aline themselves perpendicular to the pressure direction applied.We summarise our results in Fig. 4a.The pressure-T c phase diagram clearly reveals three distinct superconducting regions: the initial superconducting state (SC-I), intermediary non-superconducting state (NSC) and the pressure-induced superconducting state (SC-II). In the SC-I region between 1 bar and 8.7 GPa, T c issuppressed with applied pressure, and not detectable above 8.7 GPa. In the SC-II region, T c increases with pressure and reaches the maximum (8.1 K) at 30 GPa. Upon further compression, T c shows slow a slight decline. This is the first observation of reemerging superconductivity in one-dimensional superconductors, to the best of our knowledge.We extract the lattice parameters and volume as a function of pressure, and summarise these results in Fig. 4b. It is found that the lattice constant a displays a decrease monotonously with pressure, while the lattice constant c shows a complicated relation with pressure applied. In the SC-I region, the parameter c shrinks upon increasing pressure, but it unusually expands in the NSC region. At the pressure of 18.2 GPa, the superconductivity reemerges and the lattice constant a and c decrease simultaneously with pressure again as what is seen in the SC-I region, implying that the pressure-induced elongation effect on the wire-like sample is satuated. The pressure dependence of the volume for K2Mo3As3 is shown in the inset of the Fig. 4b, displaying that the sample volume remains almost unchanged due to the increase of parameter c and the decrease of parameter a concurrently with elevating pressure in the NSC region. The strong correlation between the lattice parameters and the superconductivity in pressurized K2Mo3As3 suggests that the remarkable change of parameter c may paly an important role for the development of the SC-II state.To understand the underlying correlation between T c and the electronic state in K2Mo3As3 further, we performed the first-principles calculations on its electronic structure, based on our XRD results, by using the projector-augmented wave (PAW) method (see the Supplemental Material [29]). We find that the percentage of the density of states (P-DOS) at Fermi level for K2Mo3As3 is dominated by the electrons from the d xy and d x2-y2 orbitals in the pressure range investigated, with a secondary contribution from the d z2,p x and p y orbitals, and the P-DOSs of the p z, d xz, d yz and sorbitals are relatively small (see the Supplemental Material [29]). We note that, in the NSC and SC-II regions, the P-DOSs of the d xy, and d x2-y2orbitals decrease continuously with elevating pressure over the experimental range investigated, however, the change trend of the P-DOSs contributed by the d z2 and the p x as well as the p y orbitals displays differently. In the NSC region, the P-DOS of the d z2 orbital exibits a remarkable increase, while that of the p orbitals shows a slow decline (Fig. 4c). As the P-DOSs of the d z2 orbital and p orbitals reach a maximum and minimum respectively, SC-II state appears. Note that the T c value of the SC-II state increases upon compression in the pressure range of 18.2 GPa – 27 GPa, just where the P-DOS of the d z2 orbital displays a decrease again. Meanwhile, the P-DOSs of the p x and p y orbitals appear an increase in the same pressure range. Further compression from 27 GPa to 40 GPa, T c of the SC-II state stays almost constant, and the corresponding P-DOSs of the d z2 and p orbitals show a small change (Fig. 4c). These results suggest that the emergence of the SC-II state in K2Mo3As3 and its T c change with pressure are the consequence of the interplay among the different orbital electrons.In conclusion, the pressure-induced reemergence of the superconductivity is observed for the first time in the qausi-one-demensional superconductor K2Mo3As3. An intimate correlation between T c’s of the ambient-pressure and high-pressure superconducting states, lattice parameters and the density of state contributed by d z2, p x and p y orbitals have been revealed. We find that the initial superconducting state (SC-I) is suppressed by pressure at 8.7 GPa, and then an intermediary non-superconducting (NSC) state sets in and stabilizes up to 18 GPa. Subsequently, a new superconduting state (SC-II) emerges and prevails up to 47.4 GPa. Our synchrotron x-ray diffraction results indicats that the reemergence of superconductivity is not associated with anycrystal structure phase transition. In combination of theoretical calculations on the band strcture, our results suggest that the appearance of the SC-II state found in this material is a consenquence of the dramatic interplay among different orbital electrons due to the pressure-induced lattice change. We hope that the results found in this study will shed new light on understanding the correlation among superconductivity, electronic and lattice structures in unconventional quasi-one dimentional superconductors.AcknowledgementsWe thank Prof. V. A. Sidorov for useful discussions. The work was supported by the National Key Research and Development Program of China (Grant No. 2017YFA0302900, 2016YFA0300300 and 2017YFA0303103), the NSF of China (Grants No. U2032214, 12004419 and 12074414) and the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (Grant No. XDB25000000). J. G. is grateful for support from the Youth Innovation Promotion Association of the CAS (2019008).*contributed equally to this work.†To whom correspondence may be addressed. Email: llsun@Reference[1].J. G. Bednorz and K. A. Müller, Possible high T c superconductivity in the Ba-La-Cu-O system, Z. Phys. B 64, 189 (1986).[2].M. K. Wu, J. R. Ashburn, C. J. Torng, P. H. Hor, R. L. Meng, L. Gao, Z. J. 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[29].See the supplementary material for electronic structure calculations; also see Refs.[30-36][30].P. E. Blöchl, Phys. Rev. B 50, 17953 (1994).[31].G. Kresse and D. Joubert, Phys. Rev. B 59, 1758 (1999).[32].G. Kresse and J. Hafner, Phys. Rev. B 47, 558 (1993).[33].G. Kresse and J. Furthmüller, Comput. Mater. Sci. 6, 15 (1996).[34].G. Kresse and J. Furthmüller, Phys. Rev. B 54, 11169 (1996).[35].J. P. Perdew, K. Burke, and M. Ernzerhof, Phys. Rev. Lett. 77, 3865 (1996).[36].H. J. Monkhorst and J. Pack, Phys. Rev. B 13, 5188 (1976).Fig. 1 (a) Resistance as a function of temperature for quausi-one-dimensional superconductor K2Mo3As3 at ambient pressure and its polycrystallined-sample’s image taken by a scanning electron microscope (inset). (b)-(d) Temperature dependence of the resistance in the pressure range of 1.2 GPa -8.7 GPa, 8.7-18.2 GPa, and 18.2-47.4 GPa, respectively. The insets of figure (b) and (d) display enlarged views of the the resistance in the low temperature regime.Fig. 2 Temperature dependence of resistance under different magnetic fields for K2Mo3As3measured at 19.6 GPa (a) and 41.8 GPa (b), respectively. (c) Plot of superconducting transition temperature T c versus critical field (H C2) for K2Mo3As3 at 19.6 GPa and 41.8 GPa, respectively. The dished lines represent the Ginzburg-Landau (GL) fits to the data of H C2.Fig. 3 X-ray diffraction patterns collected in the pressure range of 3.8 – 51.6 GPa for K2Mo3As3. The right panel schematically shows the evolution of the preferred orientation of the wire-like samples under pressures. SC-I and SC-II stand for the ambient-pressure superconducting state and the reemergence supercnducting states, respectively. NSC represents non-superconducting state.Fig 4 Superconductivity, crystal and electronic structure information for the qausi-one-dementional superconductor K2Mo3As3. (a) Pressure-Temperature phase diagram. (b) Pressure dependence of lattice parameters and volume (see inset). (c) Plots ofpercentage of the density of state (P-DOS) contrinuted by the d z2, p x and p y orbitals versus pressure.。

Current-Induced Superconductor-Insulator Transition in Granular High-T_c Superconductors

a r X i v :c o n d -m a t /0108311v 1 [c o n d -m a t .s u p r -c o n ] 20 A u g 2001CURRENT-INDUCED SUPERCONDUCTOR-INSULATOR TRANSITION INGRANULAR HIGH-T c SUPERCONDUCTORSY.Kopelevich*,C.A.M.dos Santos**,S.Moehlecke*,and A.J.S.Machado**(*)Instituto de F ´isica ”Gleb Wataghin”,Universidade Estadual de Campinas,Unicamp 13083-970,Campinas,S˜a o Paulo,Brasil(**)Departamento de Engenharia de Materiais,FAENQUIL,12600-000,Lorena,S˜a o Paulo,BrasilI.INTRODUCTIONThe occurrence of either superconducting or insulatingstate in a zero-temperature limit (T →0)under variation of system parameters such as,for instance,microscopic disorder in homogeneous thin ﬁlms [1–5]or charging en-ergy/Josephson energy ratio in granular superconductors [6,7],is one of the fundamental problems in the condensed matter physics which continuously attracts an intense re-search interest.It has also been shown both theoretically [8]and experimentally that the superconductor-insulator transition in two-dimensional (2D)superconductors can be tuned by applied magnetic ﬁeld.The ﬁeld-tuned superconductor-insulator transition has been measured in amorphous [5,9–11]and granular [12]thin ﬁlms,fabri-cated 2D Josephson-junction arrays [13,14],and bulk lay-ered quasi-2D superconductors such as high-T c cuprates [15,16].On the other hand,in granular superconductors both applied magnetic ﬁeld and electrical current aﬀect the Josephson coupling between grains [17–19].Besides,a zero-temperature current-driven dynamic transition from a vortex glass to a homogeneous ﬂow of the vortex mat-ter is expected to occur in disordered Josephson junc-tion arrays [20],suggesting the intriguing possibility of a current-induced superconductor-insulator transition,analogous to the ﬁeld-tuned transition [21].In this paper we report a systematic study of electrical current eﬀects on the superconducting properties of gran-ular high-T c superconductors.The here presented results demonstrate the occurrence of superconductor-insulator quantum phase transition driven by the applied electri-cal current,and provide evidence that the dynamics of Josephson intergranular vortices plays a crucial role in this phenomenon.II.SAMPLES AND EXPERIMENTAL DETAILSPolycrystalline single phase Y 1−x Pr x Ba 2Cu 3O 7−δsamples were prepared using a solid state reaction method with a route similar as described in [22]and char-acterized by means of x-ray powder diﬀractometry,andoptical and scanning electron microscopy.The analysis showed that the samples are granular materials consist-ing of grains with an average size d ∼5µm.The su-perconducting transition was measured both resistively and with a SQUID magnetometer MPMS5(Quantum Design).Electrical transport dc measurements in ap-plied magnetic ﬁeld H ≤100Oe,produced by a cop-per solenoid,were performed using standard four-probe technique with low-resistance (<1Ω)sputtered gold con-tacts.No heating eﬀects due to current were observed for I ≤100mA,our largest measuring current.In order to eliminate thermoelectric eﬀects,the measurements were performed inverting the applied current.Below we present the results of measurements per-formed on Y 1−x Pr x Ba 2Cu 3O 7−δsample with x =0.45close to the critical Pr concentration x c ≈0.57above which superconductivity has not been detected [22].The sample superconducting transition temperature (onset)T c 0=33K,the resistivity at the superconducting tran-sition ρN (T c 0)=20mΩcm,and dimensions l x w x t =12.6x 1.94x 1.24mm 3.III.RESULTS AND DISCUSSIONFigures 1–4present the resistance vs.temperature data obtained in a vicinity of T c 0=33K for various applied currents and magnetic ﬁelds.As Figs.1–4il-lustrate,the superconducting transition temperature on-set T c 0is both current-and ﬁeld-independent.On the other hand,the zero-resistance superconducting state is destroyed by the application of both the electrical current and magnetic ﬁeld.The superconducting order parameter Ψ=Ψ0e iφhas two components;a magnitude Ψ0and a phase φ.Be-cause T c 0(and hence Ψ0)remains unchanged,the low-temperature ﬁnite resistance in our sample originates from thermal and/or quantum ﬂuctuations in the phase locking.In the context of granular superconductors,T c 0can be identiﬁed with the transition temperature of indi-vidual grains,and the phase ﬂuctuations –with ﬂuctuat-ing Josephson currents between grains.In the absence of external ﬁeld,the critical current is that corresponding to a vortex creation and its motion,neglecting pinning.However,in granular superconductors with a very weak coupling between grains,the Earth’s magnetic ﬁeld H E ∼0.5Oe (which has not been shielded in the experiments)can easily penetrate the sample.Then,the criticalvarious at the at no variousOe. various Oe.variousOe.fromtemperatures and at no appliedﬁeld.As can be seen from Fig.5, the V(I)dependencies can be very well described by the equationV=c(T,H)(I−I th(T,H))n(T,H),(1) where I th(T,H)is the threshold current.Thus,at T=4.6K,I th=5mA and the corresponding current density(I th/cross section of the sample)j th=0.21A/cm2.T=13ﬁtting3(T=(T=8=8K);13K).ﬁeldH c 1J ∼8π2j c 0λL /c ∼0.2mOe,taking the maximum Josephson current densityj c 0∼10j th [23,26]and the typ-ical value of the intragranular London penetration depth λL ∼0.1µm (<<d).The obtained value of H c 1J is much smaller than the Earth’s magnetic ﬁeld,indeed,i.e.our sample is deeply in the mixed state.Below the threshold current I th (H,T)the vortex mo-tion is strongly suppressed or zero.The I-V charac-teristics described by the Eq.(1)are expected in the regime where the interaction between vortices and the pinning potential dominates the vortex-vortex interac-tion [20,27–29].As the applied current increases,the V(I)curves ap-proach a linear regime of ﬂux ﬂow where the diﬀerential resistance R d =dV/dI is current-independent,see Fig.6.Inset in Fig.6exempliﬁes V(I)measured at T =13K and demonstrates that at large enough currents the V(I)can be ﬁtted by the equationV (I )=R ff (I −I cf ).(2)Here R ff is the ﬂux-ﬂow resistance and I cf is the so-called dynamical critical current.In this high-current regime vortices move coherently,only weakly interacting with the pinning potential.at no K (△),13K;0.215performed at various applied ﬁelds revealed that I d (H)is a decreasing function of ﬁeld.Such a crossing has also been measured in Mo 77Ge 23ﬁlms [30]and reproduced in numerical simulations [31]which show that the pinned fraction of vortices rapidly decreases for I >I d (H).Figure 7presents typical resistance hysteresis loops R(H)measured at T =4.2K for various currents.These measurements were performed after cooling the sample from T >T c 0to the target temperature in a zero ap-plied ﬁeld.As shown in Fig.7,the resistance R cor-responding to the increasing |H |branch is larger than that corresponding to the decreasing |H |branch result-ing in “clockwise”R(H)hysteresis loops.Previous stud-ies [32–34]showed that the “clockwise”R(H)hystere-sis loops are essentially related to the granular sample structure where the resistance is determined by the mo-tion of Josephson intergranular vortices.In increasing magnetic ﬁeld larger than the ﬁrst critical ﬁeld of the grains (H >H c 1g ),the pinning prevents Abrikosov vor-tices from entering the grains,and ﬂux lines (Joseph-son vortices)are concentrated between grains leading to the intergrain ﬁeld higher than the external applied ﬁeld.When the applied ﬁeld is decreased,the pinning prevents Abrikosov vortices being expelled from the grains result-ing in a lower density of Josephson intergrain vortices as compared to that in the increasing ﬁeld.Thus,the data of Fig.7provide an unambiguous evidence that the resistance in our sample is governed by the motion of intergranular Josephson vortices in both low-and high-current limits.and I =60mA,demonstrating that the sample resistance is governed by the motion of intergranular Josephson vortices;arrows indicate the magnetic ﬁeld direction in the measure-ments.We note further that the resistance R(T)=V(T)/I in the low-temperature limit reveals a crossover from the metallic-like (dR/dT >0)to the insulating-like (dR/dT <0)behavior as the applied current isincreased,see Figs.1-4.The results presented in Figs.1-4indi-cate also the existence of a ﬁeld-dependent current I c (H),separating the metallic-like (I <I c (H))and insulating-like (I >I c (H))resistance curves,at which the resis-tance is temperature-independent.The occurrence of the temperature-independent resistance R c =(V/I)|I c can clearly be seen in Fig.8where a crossing of current-voltage I-V isotherms at I c (H)measured for two applied ﬁelds is shown.The inset in Fig.8depicts I c (H)and I d (H)which illustrates that for a given ﬁeld I c (H)>I d (H).In other words,the crossing of I-V curves takes place in the regime where the interaction between Joseph-son vortices dominates that with the pinning potential.in ).Inset to to the zero-resistance (R =0)superconducting state.With in-creasing vortex density and above some critical ﬁeld H c vortices delocalize and Bose condense,leading to the in-sulating state.The theory predicts a ﬁnite-temperature scaling law [2,3,8]which allows for experimental testing of the zero-temperature superconductor-insulator transition.It is assumed in this analysis that a sample is superconduc-tor or insulator at T =0when dR/dT >0or dR/dT <0,respectively.Besides,because the magnitude of the superconducting order parameter Ψ0(T c 0)remains unchanged on each grain as the intergranular resistance R(T,H,I)undergoes the transition from metallic-like to insulating-like behavior,the hard-core boson model [2,3,8]should be a good approximation in our analysisof the superconductor-insulator transition driven by the applied current.The resistance in the critical regime of the quantum transition is given by the equationR (δ,T )=R c f (|δ|/T 1/zν),(3)where R c is the resistance at the transition,f(|δ|/T 1/zν)is the scaling function such that f(0)=1,z and νare critical exponents,and δis the deviation of a variable parameter from its critical value.Assuming δ=I -I c (δ=H -H c in the case of a ﬁeld-tuned transition)we plotted in Figs.9-11,R =V/I vs.|δ|/T 1/αfor three applied ﬁelds.In each case,the exponent αwas obtained from log-log plots of (dR/dI)|I c vs.T −1.The expected collapse of the resistance data onto two branches distin-guishing the I <I c from the I >I c data is very clear in Figs.9-11.scaling =16.26.7K scaling mA,(△),T the re-sults presented in Figs.9-11should be considered as empirical ones,the very good scalingﬁt strongly suggests the occurrence of a zero-temperature current-induced superconductor-insulator transition.Notably,the here found exponentsαagree nicely with most of the data obtained in the scaling analysis of theﬁeld-tuned transi-tion[5,9–16].scalingmA,α),T= In conclusion,we would like to emphasize that the here studied superconductor-insulator transition driven by the electrical current is essentially related to the dynamics of Josephson intergranular vortices.Actually,as the above results demonstrate,the crossing of I-V characteristics takes place in theﬂuxﬂow regime.We stress that the crossover current I c(H)is smaller than the maximum su-percurrent I0=(2e/ )E J(E J is the Josephson coupling energy)that the Josephson junctions can support.In other words,both tunneling Cooper pairs and moving Josephson vortices are present at the I c(H)which play a dual role as discussed in the context of theﬁeld-tuned transition[8].A self-consistent analysis would require the existence of zero-temperature“depinning”transition in the Joseph-son vortex matter driven by the applied current.The occurrence of such a transition in disordered Josephson junction arrays has theoretically been predicted,indeed [20].All these indicate that the current-induced superconductor-insulator transition can be considered as the dynamical counterpart of the magnetic-ﬁeld-tuned transition.Finally,we point out that similar results were obtained on Y1−x Pr x Ba2Cu3O7−δ(x=0.5)and Bi2Sr2Ca1−x Pr x Cu2O8+δ(x=0.54)granular supercon-ductors.V.ACKNOWLEDGEMENTSThe authors would like to thank Enzo Granato for the fruitful discussions.This study was supported by FAPESP and CNPq Brazilian science agencies.New Superconductors”in H.Ehrenreich and D.Turnbull (eds.)Solid State Phys.42(1989)91.[26]C.J.Lobb,D.W.Abraham,and M.Tinkham,Phys.Rev.B27(1983)150.[27]P.Berghuis and P.H.Kes,Phys.Rev.B47(1993)262.[28]S.Bhattacharya and M.J.Higgins,Phys.Rev.Lett.70(1993)2617.[29]Y.Enomoto,K.Katsumi,and S.Maekawa,Physica C215(1993)51.[30]M.C.Hellerqvist,D.Ephron,W.R.White,M.R.Beasly,and A.Kapitulnik,Phys.Rev.Lett.76(1996)4022;M.C.Hellerqvist and A.Kapitulnik,Phys.Rev.B56(1997)5521.[31]S.Ryu,M.Hellerqvist,S.Doniach,A.Kapitulnik,andD.Stroud,Phys.Rev.Lett.77(1996)5114.[32]Y.Kopelevich,V.V.Lemanov,and V.V.Makarov,Sov.Phys.Solid State32(1990)2095;V.V.Makarov and Y.Kopelevich,Phys.Rev.B54(1996)84.[33]L.Ji,M.S.Rzchowski,N.Anand,and M.Tinkham,Phys.Rev.B47(1993)470.[34]S.Li,M.Fistul,J.Deak,P.Metcalf,and M.McElfresh,Phys.Rev.B52(1995)747.。

作文未来超导技术450字的

作文未来超导技术450字的英文回答：Superconducting technology is poised to revolutionize various industries and sectors in the future. With itsability to conduct electricity with zero resistance, superconductors have the potential to greatly enhanceenergy efficiency, transportation systems, and even medical applications.In terms of energy efficiency, superconductingmaterials can significantly reduce energy loss during transmission and distribution. This means that electricity can be transmitted over long distances without any loss of power, leading to more efficient and cost-effective energy systems. This technology can also be applied to power grids, allowing for better management and stability.In the transportation sector, superconductors can revolutionize the way we travel. Magnetic levitation(maglev) trains, which use superconducting magnets to float above the tracks, can achieve incredible speeds and efficiency. This technology has the potential to transform long-distance travel, making it faster, safer, and more environmentally friendly.Furthermore, superconducting technology can greatly benefit the medical field. Magnetic resonance imaging (MRI) machines, which use superconducting magnets, provide detailed and accurate images of the human body. This technology has revolutionized medical diagnosis and treatment, allowing for earlier detection of diseases and more precise surgical procedures.In conclusion, the future of superconducting technology is bright. Its potential to enhance energy efficiency, revolutionize transportation, and improve medical applications cannot be overstated. As research and development in this field continue to advance, we can expect to see even more innovative and practical applications of superconductors in the near future.中文回答：超导技术有望在未来革新各个行业和领域。

Two gaps make a high-temperature superconductor

IOP P UBLISHING R EPORTS ON P ROGRESS IN P HYSICS Rep.Prog.Phys.71(2008)062501(9pp)doi:10.1088/0034-4885/71/6/062501Two gaps make a high-temperature superconductor?S H¨ufner1,2,M A Hossain1,2,A Damascelli1,2and G A Sawatzky1,21AMPEL,University of British Columbia,Vancouver,British Columbia,V6T1Z4,Canada2Department of Physics and Astronomy,University of British Columbia,Vancouver,British Columbia,V6T1Z1,CanadaReceived27February2008,inﬁnal form2April2008Published2May2008Online at /RoPP/71/062501AbstractOne of the keys to the high-temperature superconductivity puzzle is the identiﬁcation of theenergy scales associated with the emergence of a coherent condensate of superconductingelectron pairs.These might provide a measure of the pairing strength and of the coherence ofthe superﬂuid,and ultimately reveal the nature of the elusive pairing mechanism in thesuperconducting cuprates.To this end,a great deal of effort has been devoted to investigatingthe connection between the superconducting transition temperature T c and the normal-statepseudogap crossover temperature T∗.Here we present a review of a large body ofexperimental data which suggests a coexisting two-gap scenario,i.e.superconducting gap andpseudogap,over the whole superconducting dome.We focus on spectroscopic data fromcuprate systems characterized by T maxc ∼95K,such as Bi2Sr2CaCu2O8+δ,YBa2Cu3O7−δ,Tl2Ba2CuO6+δand HgBa2CuO4+δ,with particular emphasis on the Bi-compound which has been the most extensively studied with single-particle spectroscopies.(Someﬁgures in this article are in colour only in the electronic version)This article was invited by Professor L Greene.Contents1.Introduction12.Emerging phenomenology32.1.Angle-resolved photoemission42.2.Tunneling52.3.Raman scattering52.4.Inelastic neutron scattering52.5.Heat conductivity63.Outlook and conclusion6 Acknowledgments6 References71.IntroductionSince their discovery[1],the copper-oxide high-T c superconductors(HTSCs)have become one of the most investigated class of solids[2–24].However,despite the intense theoretical and experimental scrutiny,an understanding of the mechanism that leads to superconductivity is still lacking.At the very basic level,what distinguishes the cuprates from the conventional superconductors is the fact that they are doped materials,the highly atomic-like Cu 3d orbitals give rise to strong electron correlations(e.g. the undoped parent compounds are antiferromagnetic Mott–Hubbard-like insulators),and the superconducting elements are weakly-coupled two-dimensional layers(i.e.the celebrated square CuO2planes).Among the properties that are unique to this class of superconducting materials,in addition to the unprecedented high superconducting T c,the normal-state gap or pseudogap is perhaps the most noteworthy.The pseudogap wasﬁrst detected in the temperature dependence of the spin-lattice relaxation and Knight shift in nuclear magnetic resonance and magnetic susceptibility studies[25].The Knight shift is proportional to the density of states at the Fermi energy;a gradual depletion was observed below a crossover temperature T∗,revealing the opening of the pseudogap well above T c on the underdoped side of the HTSC phase diagram(ﬁgure1).As the estimates based on thermodynamicx (c)Tx (a)x(b)T* T cT*T cT*T cFigure1.Various scenarios for the interplay of pseudogap(blue dashed line)and superconductivity(red solid line)in thetemperature-doping phase diagram of the HTSCs.While in(a)the pseudogap merges gradually with the superconducting gap in the strongly overdoped region,in(b)and(c)the pseudogap lines intersect the superconducting dome at about optimal doping(i.e.maximum T c).In most descriptions,the pseudogap line is identiﬁed with a crossover with a characteristic temperature T∗rather than a phase transition;while at all dopings T∗>T c in(a),beyond optimal doping T∗<T c in(b)and T∗does not even exist in(c).Adapted from[12].quantities are less direct than in spectroscopy we,in the course of this review,concentrate mainly on spectroscopic results; more information on other techniques can be found in the literature[5].As established by a number of spectroscopic probes, primarily angle-resolved photoemission spectroscopy,[26,27] the pseudogap manifests itself as a suppression of the normal-state electronic density of states at E F exhibiting a momentum dependence reminiscent of a d x2−y2functional form.For hole-doped cuprates,it is largest at Fermi momenta close to the antinodal region in the Brillouin zone—i.e.around (π,0)—and vanishes along the nodal direction—i.e.the(0,0) to the(π,π)line.Note however that,strictly speaking, photoemission and tunneling probe a suppression of spectral weight in the single-particle spectral function,rather than directly of density of states;to address this distinction,which is fundamental in many-body systems and will not be further discussed here,it would be very interesting to investigate the quantitative correspondence between nuclear magnetic resonance and single-particle spectroscopy results.Also,no phase information is available for the pseudogap since,unlike the case of optimally and overdoped HTSCs[28],no phase-sensitive experiments have been reported for the underdoped regime where T∗ T c.As for the doping dependence,the pseudogap T∗is much larger than the superconducting T c in underdoped samples,it smoothly decreases upon increasing the doping,and seems to merge with T c in the overdoped regime,eventually disappearing together with superconductivity at doping levels larger than x∼0.27[5–24].In order to elaborate on the connection between pseudogap and high-T c superconductivity,or in other words between the two energy scales E pg and E sc identiﬁed by T∗and T c,respectively,let us start by recalling that in conventional superconductors the onset of superconductivity is accompanied by the opening of a gap at the chemical potential in the one-electron density of states. According to the Bardeen–Cooper–Schrieffer(BCS)theory of superconductivity[29],the gap energy provides a direct measure of the binding energy of the two electrons forming a Cooper pair(the two-particle bosonic entity that characterizes the superconducting state).It therefore came as a great surprise that a gap,i.e.the pseudogap,was observed in the HTSCs not only in the superconducting state as expected from BCS, but also well above T c.Because of these properties and the hope it might reveal the mechanism for high-temperature superconductivity,the pseudogap phenomenon has been very intensely investigated.However,no general consensus has been reached yet on its origin,its role in the onset of superconductivity itself,and not even on its evolution across the HTSC phase diagram.As discussed in three recent papers on the subject [12,15,17],and here summarized inﬁgure1,three different phase diagrams are usually considered with respect to the pseudogap line.While Millis[15]opts for a diagram like the one inﬁgure1(a),Cho[17]prefers a situation where the pseudogap line meets the superconducting dome at x 0.16(ﬁgures1(b)and(c));Norman et al[12]provide a comprehensive discussion of the three different possibilities. One can summarize some of the key questions surrounding the pseudogap phenomenon and its relevance to high-temperature superconductivity as follows[12,15,17]:1.Which is the correct phase diagram with respect to thepseudogap line?2.Does the pseudogap connect to the insulator quasiparticlespectrum?3.Is the pseudogap the result of some one-particle bandstructure effect?4.Or,alternatively,is it a signature of a two-particle pairinginteraction?5.Is there a true order parameter deﬁning the existence of apseudogap phase?6.Do the pseudogap and a separate superconducting gapcoexist below T c?7.Is the pseudogap a necessary ingredient for high-T csuperconductivity?In this review we revisit some of these questions,with speciﬁc emphasis on the one-versus two-gap debate.Recently,this latter aspect of the HTSCs has been discussed in great detail by Goss Levi[30],in particular based on scanning-tunneling microscopy data from various groups[31–33].Here we expand this discussion to include the plethora of experimental results available from a wide variety of techniques.We0.050.100.150.200.250408012016050100150E n e r g y (m e V )Hole doping (x)T c (K )Figure 2.Pseudogap (E pg =2 pg )and superconducting (E sc ∼5k B T c )energy scales for a number of HTSCs with T max c ∼95K(Bi2212,Y123,Tl2201and Hg1201).The datapoints were obtained,as a function of hole doping x ,by angle-resolved photoemission spectroscopy (ARPES),tunneling (STM,SIN,SIS),Andreev reﬂection (AR),Raman scattering (RS)and heat conductivity (HC).On the same plot we are also including the energy r of the magnetic resonance mode measured by inelastic neutron scattering (INS),which we identify with E sc because of the striking quantitative correspondence as a function of T c .The data fall on two universal curvesgiven by E pg =E max pg (0.27−x)/0.22and E sc =E max sc [1−82.6(0.16−x)2],with E maxpg =E pg (x =0.05)=152±8meV and E maxsc =E sc (x =0.16)=42±2meV (the statistical errors refer to the ﬁt of the selected datapoints;however,the spread of all available data would be more appropriately described by ±20and ±10meV ,respectively).show that one fundamental and robust conclusion can be drawn:the HTSC phase diagram is dominated by two energy scales,the superconducting transition temperature T c and the pseudogap crossover temperature T ∗,which converge to the very same critical point at the end of the superconducting dome.Establishing whether this phenomenology can be conclusively described in terms of a coexisting two-gap scenario,and what the precise nature of the gaps would be,will require a more deﬁnite understanding of the quantities measured by the various probes.2.Emerging phenomenologyThe literature on the HTSC superconducting gap and/or pseudogap is very extensive and still growing.In this situation it seems interesting to go over the largest number of data obtained from as many experimental techniques as possible,and look for any possible systematic behavior that could be identiﬁed.This is the primary goal of this focused review.We want to emphasize right from the start that we are not aiming at providing exact quantitative estimates of superconducting and pseudogap energy scales for any speciﬁc compound or any given doping.Rather,we want to identify the general phenomenological picture emerging from the whole body of available experimental data [5,9,13,16,18,34–72].We consider some of the most direct probes of low-energy,electronic excitations and spectral gaps,such as angle-resolved photoemission (ARPES),scanning-tunneling microscopy (STM),superconductor/insulator/normal-metal(SIN)and superconductor/insulator/superconductor (SIS)tunneling,Andreev reﬂection tunneling (AR)and Raman scattering (RS),as well as less conventional probes such as heat conductivity (HC)and inelastic neutron scattering (INS).The emphasis in this review is on spectroscopic data because of their more direct interpretative signiﬁcance;however,these will be checked against thermodynamic/transport data whenever possible.With respect to the spectroscopic data,it is important to differentiate between single-particle probes such as ARPES and STM,which directly measure the one-electron excitation energy with respect to the chemical potential (on both side of E F in STM),and two-particle probes such as Raman and inelastic neutron scattering,which instead provide information on the particle-hole excitation energy 2 .Note that the values reported here are those for the ‘full gap’2 (associated with either E sc or E pg ),while frequently only half the gap is given for instance in the ARPES literature.In doing so one implicitly assumes that the chemical potential lies half-way between the lowest-energy single-electron removal and addition states;this might not necessarily be correct but appears to be supported by the direct comparison between ARPES and STM/Raman results.A more detailed discussion of the quantities measured by the different experiments and their interpretation is provided in the following subsections.Here we would like to point out that studies of B 2g and B 1g Raman intensity [19,40,52],heat conductivity of nodal quasiparticles [70,71]and neutron magnetic resonance energy r [42]do show remarkable agreement with superconducting or pseudogap energy scales as inferred by single-particleTable1.Pseudogap E pg and superconducting E sc energy scales (2 )as inferred,for optimally doped Bi2212(T c∼90–95K),from different techniques and experiments.Abbreviations are given in the main text,while the original references are listed.Experiment Energy meV ReferencesARPES—(π,0)peak E pg80[34,35]Tunneling—STM…70[18,36]Tunneling—SIN…85[37]Tunneling—SIS…75[38,39]Raman—B1g…65[40]Electrodynamics…80[5,41]Neutron—(π,π) r E sc40[42]Raman—B2g…45[40]Andreev…45[43]SIS—dip…40[39]probes,or with the doping dependence of T c itself.Thus they provide,in our opinion,an additional estimate of E sc and E pg energy scales.As for the choice of the speciﬁc compounds to include in our analysis,we decided to focus on those HTSCs exhibiting a similar value of the maximum superconductingtransition temperature T maxc ,as achieved at optimal doping,so that the data could be quantitatively compared without any rescaling.We have therefore selected Bi2Sr2CaCu2O8+δ(Bi2212),YBa2Cu3O7−δ(Y123),Tl2Ba2CuO6+δ(Tl2201) and HgBa2CuO4+δ(Hg1201),which have been extensivelyinvestigated and are all characterized by T maxc ∼95K[73](with particular emphasis on Bi2212,for which the most extensive set of single-particle spectroscopy data is available). It should also be noted that while Bi2212and Y123are ‘bilayer’systems,i.e.their crystal structure contains as a key structural element sets of two adjacent CuO2layers, Tl2201and Hg1201are structurally simpler single CuO2-layer materials.Therefore,this choice of compounds ensures that our conclusions are generic to all HTSCs with a similar T c, independent of the number of CuO2layers.A compilation of experimental results for the magnitude of pseudogap(E pg=2 pg)and superconducting(E sc∼5kB T c) energy scales,as a function of carrier doping x,is presented inﬁgure2(only some representative datapoints are shown,so as not to overload theﬁgure;similar compilations were also obtained by a number of other authors)[5,9,13,16,42,43,52, 57,60,70,74,75].The data for these HTSCs with comparableT max c ∼95K fall on two universal curves:a straight linefor the pseudogap energy E pg=2 pg and a parabola for the superconducting energy scale E sc∼5k B T c.The two curves converge to the same x∼0.27critical point at the end of the superconducting dome,similarly to the cartoon of ﬁgure1(a).In order to summarize the situation with respect to quantitative estimates of E pg and E sc,we have listed in table1the values as determined by the different experimental techniques on optimally doped Bi2212(with T c ranging from 90to95K).While one obtains from this compilation the average values of E pg 76meV and E sc 41meV at optimal doping,the numbers do scatter considerably.Note also that these numbers differ slightly from those given in relation to the parabolic and straight lines inﬁgure2(e.g.E maxsc= 42meV)because the latter were inferred from aﬁtting of superconducting and pseudogap data over the whole doping range,while those in table1were deduced from results for optimally doped Bi2212only.It is also possible to plot the pseudogap E pg and superconducting E sc energy scales as estimated simultaneously in one single experiment on the very same sample.This is done inﬁgure3for Raman,tunneling and ARPES results from Bi2212and Hg1201,which provide evidence for the presence of two energy scales,or possibly two spectral gaps as we discuss in greater detail below,coexisting over the whole superconducting dome.2.1.Angle-resolved photoemissionThe most extensive investigation of excitation gaps in HTSCs has arguably been done by ARPES[9,10,26,27,34,35,54–66,76–80].This technique provides direct access to the one-electron removal spectrum of the many-body system;it allows,for instance in the case of a BCS superconductor[29], to measure the momentum dependence of the absolute value of the pairing amplitude2 via the excitation gap observed for single-electron removal energies,again assuming E F to be located half-way in the gap[9,10].This is the same in some tunneling experiments such as STM,which however do not provide direct momentum resolution but measure on both sides of E F[18].The gap magnitude is usually inferred from the ARPES spectra from along the normal-state Fermi surface in the antinodal region,where the d-wave gap is largest;it is estimated from the shift to high-binding energy of the quasiparticle spectral weight relative to the Fermi energy.With this approach only one gap is observed below a temperature scale that smoothly evolves from the so-called pseudogap temperature T∗in the underdoped regime,to the superconducting T c on the overdoped side.We identify this gap0.050.100.150.200.25408012016050100150Energy(meV)Hole doping (x)T c(K)Figure3.Pseudogap E pg and superconducting E sc energy scales (2 )as estimated,by a number of probes and for different compounds,in one single experiment on the very same sample. These data provide direct evidence for the simultaneous presenceof two energy scales,possibly two spectral gaps,coexisting in the superconducting state.The superconducting and pseudogap lines are deﬁned as inﬁgure2.with the pseudogap energy scale E pg=2 pg.This is also in agreement with recent investigations of the near-nodal ARPES spectra from single and double layer Bi-cuprates[57,76,77], which further previous studies of the underdoped cuprates’Fermi arc phenomenology[78–80].From the detailed momentum dependence of the excitation gap along the Fermi surface contour,and the different temperature trends observed in the nodal and antinodal regions,these studies suggest the coexistence of two distinct spectral gap components over the whole superconducting dome:superconducting gap and pseudogap,dominating the response in the nodal and antinodal regions,respectively,which would eventually collapse to one single energy scale in the very overdoped regime.2.2.TunnelingThe HTSCs have been investigated by a wide variety of tunneling techniques[13,18,36–39,44–51],such as SIN[38,51],SIS[37–39],STM[18,36,46],intrinsic tunneling[47–50]and Andreev reﬂection,which is also a tunneling experiment but involves two-particle rather than single-particle tunneling(in principle,very much like SIS) [13,43,72].All these techniques,with the exception of intrinsic tunneling3,are represented here either in theﬁgures or table.Similarly to what was discussed for ARPES at the antinodes,there are many STM studies that report a pseudogap E pg smoothly evolving into E sc upon overdoping[18,31]. In addition,a very recent temperature-dependent study of overdoped single-layer Bi-cuprate detected two coexisting,yet clearly distinct,energy scales in a single STM experiment[32]. In particular,while the pseudogap was clearly discernible in the differential conductance exhibiting the usual large spatial modulation,the evidence for a spatially uniform superconducting gap was obtained by normalizing the low-temperature spectra by those just above T c 15K.These values have not been included inﬁgures2and3because T c 95K;however,this study arguably provides the most direct evidence for the coexistence of two distinct excitation gaps in the HTSCs.One can regard Andreev reﬂection(pair creation in addition to a hole)as the inverse of a two-particle scattering experiment such as Raman or INS.A different view is also possible:SIN tunneling goes over to AR if the insulator layer gets thinner and thinner[13];thus a SIN tunneling,as also STM,should give the same result as AR.However while SIN and STM measure the pseudogap,AR appears to be sensitive to the superconducting energy scale E sc(ﬁgure2).We can only conjecture that this has to do with the tunneling mechanisms actually being different.3The most convincing tunneling results showing two coexisting gaps were actually obtained by intrinsic tunneling[47–50],in particular from Bi2Sr2CuO6+δ(Bi2201)[48].However,because this technique suffers from systematic problems[50],and one would anyway have to scale the Bi2201data because of the lower value of T c and in turn gap energy scales,these results were not included inﬁgures2or3.Since intrinsic tunneling is in principle a clean SIS experiment which measures pair energies through Josephson tunneling, a reﬁnement of the technique might provide an accurate estimate of both superconducting and pseudogap simultaneously,and is thus highly desirable.SIS tunneling experiments[39]ﬁnd E pg/E sc 1for Bi2212at all doping levels.There are,however,some open questions concerning the interpretation of the SIS experiments. This technique,which exploits Josephson tunneling,measures pair spectra;the magnitude of E pg can readily be obtained from the most pronounced features in the spectra[39].The signal related to E sc is seen as a‘sideband’on the E pg features;it does not seem obvious why,if the E sc signal did originate from a state of paired electrons,it would not show up more explicitly.2.3.Raman scatteringLight scattering measures a two-particle excitation spectrum providing direct insight into the total energy needed to break up a two-particle bound state or remove a pair from a condensate. Raman experiments can probe both superconducting and pseudogap energy scales,if one interprets the polarization dependent scattering intensity in terms of different momentum averages of the d-wave-like gap functions:one peaked at(π,0) in B1g geometry,and thus more sensitive to the larger E pg which dominates this region of momentum space;the other at(π/2,π/2)in B2g geometry,and provides an estimate of the slope of the gap function about the nodes,(1/¯h)(d /d k)|n, which is more sensitive to the arguably steeper functional dependence of E sc out of the nodes[19,40,52,53].One should note,however,that the signal is often riding on a high background,which might result in a considerable error and data scattering.At a more fundamental level,while the experiments in the antinodal geometry allow a straightforward determination of the gap magnitude E pg,the nodal results need a numerical analysis involving a normalization of the Raman response function over the whole Brillouin zone,a procedure based on a low-energy B2g sum rule(although also the B2g peak position leads to similar conclusions)[52].This is because a B2g Raman experiment is somewhat sensitive also to the gap in the antinodal direction,where it picks up,in particular,the contribution from the larger pseudogap.2.4.Inelastic neutron scatteringInelastic neutron scattering experiments have detected the so-called q=(π,π)resonant magnetic mode in all of the T c 95K HTSCs considered here[16].This resonance is proposed by some to be a truly collective magnetic mode that, much in the same way as phonons mediate superconductivity in the conventional BCS superconductors,might constitute the bosonic excitation mediating superconductivity in the HTSCs. The total measured intensity,however,amounts to only a small portion of what is expected based on the sum rule for the magnetic scattering from a spin1/2system[8,16,24, 42,68,69];this weakness of the magnetic response should be part of the considerations in the modeling of magnetic resonance mediated high-T c superconductivity.Alternatively, its detection below T c might be a mere consequence of the onset of superconductivity and of the corresponding suppression of quasiparticle scattering.Independently of the precise interpretation,the INS data reproduced inﬁgure2show that the magnetic resonance energy r tracks very closely, over the whole superconducting dome,the superconductingenergy scale E sc∼5k B T c(similar behavior is observed, in the underdoped regime,also for the spin-gap at the incommensurate momentum transfer(π,π±δ)[81]).Also remarkable is the correspondence between the energy of the magnetic resonance and that of the B2g Raman peak.Note that while the q=(π,π)momentum transfer observed for the magnetic resonance in INS is a key ingredient of most proposed HTSC descriptions,Raman scattering is a q=0probe.It seems that understanding the connection between Raman and INS might reveal very important clues.2.5.Heat conductivityHeat conductivity data from Y123and Tl2201fall onto the pseudogap line.This is a somewhat puzzling result because they have been measured at very low temperatures,well into the superconducting state,and should in principle provide a measure of both gaps together if these were indeed coexisting below T c.However,similarly to the B2g Raman scattering, these experiments are only sensitive to the slope of the gap function along the Fermi surface at the nodes,(1/¯h)(d /d k)|n; the gap itself is determined through an extrapolation procedure in which only one gap was assumed.The fact that the gap values,especially for Y123,come out on the high side of the pseudogap line may be an indication that an analysis with two coexisting gaps might be more appropriate.3.Outlook and conclusionThe data inﬁgures2and3demonstrate that there are two coexisting energy scales in the HTSCs:one associated with the superconducting T c and the other,as inferred primarily from the antinodal region properties,with the pseudogap T∗. The next most critical step is that of addressing the subtle questions concerning the nature of these energy scales and the signiﬁcance of the emerging two-gap phenomenology towards the development of a microscopic description of high-T c superconductivity.As for the pseudogap,which grows upon underdoping, it seems natural to seek a connection to the physics of the insulating parent compound.Indeed,it has been pointed out that this higher energy scale might smoothly evolve,upon underdoping,into the quasiparticle dispersion observed by ARPES in the undoped antiferromagnetic insulator[82,83]. At zero doping the dispersion and quasiparticle weight in the single-hole spectral function as seen by ARPES can be very well explained in terms of a self-consistent Born approximation[84],as well as in the diagrammatic quantum Monte Carlo[85]solution to the so-called t–t –t –J model.In this model,as in the experiment[82,83],the energy difference between the top of the valence band at(π/2,π/2)and the antinodal region at(π,0)is a gap due to the quasiparticle dispersion of about250±30meV.Note that this would be a single-particle gap .For the direct comparison with the pseudogap data inﬁgure2,we would have to consider 2 ∼500meV;this,however,is much larger than the x=0 extrapolated pseudogap value of186meV found from our analysis across the phase diagram.Thus there seems to be an important disconnection between theﬁnite doping pseudogapand the zero-doping quasiparticle dispersion.The fact that the pseudogap measured in ARPES and SINexperiments is only half the size of the gap in SIS,STM,B1gRaman and heat conductivity measurements,points to a pairinggap.So although the origin of the pseudogap atﬁnite dopingremains uncertain,we are of the opinion that it most likelyreﬂects a pairing energy of some sort.To this end,the trend inﬁgure2brings additional support to the picture discussed bymany authors that the reduction in the density of states at T∗isassociated with the formation of electron pairs,well above theonset of phase coherence taking place at T c(see,e.g.[86,87]).The pseudogap energy E pg=2 pg would then be the energy needed to break up a preformed pair.To conclusively addressthis point,it would be important to study very carefully thetemperature dependence of the(π,0)response below T c;anyfurther change with the onset of superconductivity,i.e.anincrease in E pg,would conﬁrm the two-particle pairing picture,while a lack thereof would suggest a one-particle band structureeffect as a more likely interpretation of the pseudogap.The lower energy scale connected to the superconductingT c(parabolic curve inﬁgure2and3)has already been proposedby many authors to be associated with the condensationenergy[86–89],as well as with the magnetic resonance inINS[90].One might think of it as the energy needed totake a pair of electrons out of the condensate;however,fora condensate of charged bosons,a description in terms of acollective excitation,such as a plasmon or roton,would bemore appropriate[24].The collective excitation energy wouldthen be related to the superﬂuid density and in turn to T c.In thissense,this excitation would truly be a two-particle process andshould not be measurable by single-particle spectroscopies.Also,if the present interpretation is correct,this excitationwould probe predominantly the charge-response of the system;however,there must be a coupling to the spin channel,so as tomake this process neutron active(yet not as intense as predictedby the sum rule for pure spin-1/2magnetic excitations,whichis consistent with the small spectral weight observed by INS).As discussed,one aspect that needs to be addressed to validatethese conjectures is the surprising correspondence betweenq=0and q=(π,π)excitations,as probed by Raman andINS,respectively.We are led to the conclusion that the coexistence of twoenergy scales is essential for high-T c superconductivity,withthe pseudogap reﬂecting the pairing strength and the other,always smaller than the pseudogap,the superconductingcondensation energy.This supports the proposals thatthe HTSCs cannot be considered as classical BCSsuperconductors,but rather are smoothly evolving from theBEC into the BCS regime[91–93],as carrier doping isincreased from the underdoped to the overdoped side of thephase diagram.AcknowledgmentsSH would like to thank the University of British Columbiafor its hospitality.Helpful discussions with W N Hardy,。

固_固接触界面热传输研究 2008

式表明, 热导率与平均自由程成正比。结合界面
厚度的分析, 界面层热导率是否如体材热导率一
样, 是一种本质属性, 值得深入细致地研究。因为
界面层内热载子的平均自由程会随界面层的几何
厚度不同而变化, 导致热导率也会发生变化, 所以
界面层热导率还取决于几何参数 ) ) ) 界面层厚度。
图 4 界面层上的热载子传输示意图
种接触, 界面层厚度 D具有与两个扩散极限之和

D1 + D2 相同的量级 ) ) ) 微米量级, D~ ( D1 + D2 )。
综合以上三种接触界面层厚度的界定, 在纳
微米厚度范围内的接触界面层内, 热载子 (声子、
电子、光子 )存在散射、扩散、反射、辐射等行为,
这些行为使热载子的平均自由程受到限制而变
关键词: 接触界面层; 热载子; 微尺度传热; 接触热传导
The invest iga tion of solid- solid contact in terfa ce th erm a l tr an sfer
Sh i Ling1, Yu X inm ing1, W angH uiling2, W u Xue jun1 ( 1. School of Chem istry and Environm ent Engineer ing, Jianghan Un iversity, Wuhan 430056, Ch ina; 2. Laboratory of Cryogen ics, H uazhong Un iversity of Sc ience and Technology, W uhan 430074, Ch ina) Abstr ac t: The concept of contact inte rface laye r was exp la ined. Based on the contact inte rface laye r, the th ickness and therma l conductivity of contact in terface laye r we re discussed, and the d iffusive and radiative therm a l conduction were occurred in contact inter face layer. The m echanism ofm icro- structure was shown up. The contact interface therm al resistance m ode l( C ITR ) was set up, the calcu lated va lue of the CITR was com pared with the va lue of DMM and exper im enta l datum, the results show that the lim ita tion of the DMM is hurd led. These are he lpful of the m icro- structure therm al transfer ana lysis. K eyword s: Contact interface layer, Therm al carr ie r, M icro- sca le the rm al transfe r, Contact conduction

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Applied High-Tc Superconducting Electrical MachinesTsutomu Hoshino,Itsuya Muta,Taketsune Nakamura,Graduate School of Engineering,Kyoto University,Sakyo-ku,Kyoto 606-8501,Japane-mailhoshino@asl.kuee.kyoto-u.ac.jpABSTRACT –Superconductivity is key technol-ogy for 21st century.To suppress emission of green house eﬀect gas,applied superconductivity is impor-tant.In this paper,the current status of supercon-ducting power machines such as generator and mo-tor are described.Most of all studies are the step of demonstration of idea and possibility.There are large gap between physical idea and actual appara-tus.Further collaboration between scientists and en-gineers has been required.1.IntroductionUse of conventional energy fuels (such as oil,nat-ural gas,and coal)leads to the green house eﬀect that is responsible for global warming,and to the acid rains that greatly damage the agricultural lands.Emissions of diﬀerent parts of the world to the suc-cessively increase in CO 2concentrations are shown in Fig.1.Some 160nations adopted the historic Kyoto Protocol 11December 1997at the global warming conference formally known as the Third Conference of Parties to the United Nations Framework Conven-tion on Climate Change (COP3).The draft agree-ment,which must be ratiﬁed by 55countries,calls on industrialized nations to cut six greenhouse gases (carbon dioxide,methane,nitrous oxide and three ﬂuorine compounds)by average of 5.2percent be-tween 2008and 2012.Delegates will again take up the heavily debated issue of emissions trading at the 1998Buenos Aires climate change conference.Un-1970198019902000Fiscal YearC O 2 (c a r b o n M t )Fig.1CO 2emission of diﬀerent parts of the world[1].Table 1R &D Status of Superconducting ElectricalMachines.apparatus type status generator homopolar L=Cﬁeld superconducting L=C,H=B fully superconducting L=B,H=Amotor synchronous machine A ∼Blinear induction A ∼C linear synchronous A ∼C ﬂux pump A ∼Cphase com-pensator synchronous compen-satorC A:basic technology,B:feasibility study,C:practica-bility veriﬁcation,L:low temperature superconduc-tor,H:high temperature superconductorder its terms,38developed nations agreed to reduce world-wide emissions.These countries are divided into eight groups,and their “targets”range from a reduction of 8percent to and increase of 10percent [1].Applied superconductivity is one of solutions to decrease such emissions.There are many applied superconducting apparatus,such as:generator,mo-tor,rotating condenser,transformer,reactor,SMES,power transmission cable,current lead,current lim-iter,magnetic bearing,magnetic separation,mag-netic stirrer,magnetic brake,MRI,magnetic levi-tation,digital information processing device,milli-submilli-meter wave sensor,magnetic measurement for living body.In this paper the current status of superconducting power machines are summarized as shown in Table 1especially HTS application [2].2.GeneratorSuperconducting AC generators which are being actively studied in various countries have many mer-its compared with conventional generators,e.g.,im-provement of eﬃciency,power system stability and operation performances,and reduction in size and weight,etc.First generator was developed by MIT.Furthermore,France,Russia,China,Japan,Korea and India are promoting the development.In Japan,it has been progressed as a project of the Agency of Instudrial Science and Technology of MITI and the demonstration test of 70MW generator have been continued as the ﬁnal stage of 12years.In Korea,3year project of 1MW geneator has been carred out by Korea Electrotechnology Research Institute.In these researches low temperature superconductorFig.2HTS rotor and stator assembly[3]. (LTS)was used.Available characteristics of LTS is not enough to introduce these generators.GE Corporate Research(U.S.A.)started100MVA HTS rotatingﬁeld winding type synchronous gener-ator,which operated at16∼25K from1993.Its purpose was(1)generator design,element develop-ment and evaluation of energy and economics,(2) HTS wire development,prototype saddle shape coil fabrication.This project quitted until development of proper HTS wire.Westinghouse Science&Technology Center and American Superconductor Corporation present con-ceptual design of1MW generator for Mobile Radar (MR)applications as shown in Fig.2[3].Theﬁeld winding of generator consists of HTS coils.The cool-ing of theﬁeld winding is provided by heat exchange with helium gas cooled by a Giﬀord-McMahon cry-ocooler.Total losses are estimated as10343W.This work was supported by the Ballistic Missile Defense Organization and the Air Force Research Laboratory Propulsion Directorate.Kovalev et al.reported two types of alternators[4].Theﬁrst is a synchronous machine containinga stationaryﬁeld winding made from HTS Bi-based were placed into a cryostat,which is cooled by liq-uid hydrogen.it may be seen that critical current becomes10times higher at LH2temperature.This machine provides the output power3kVA for rotat-ing speed12000rpm.The second alternator is an electrical machine consisting of a conventional three phase stator winding and the rotor is constructed from bulk YBCO elements.3.Motor60%of power demand is from the motor load.The 70%of motor demand is occupied by large scale mo-tor such as over350kW.If one to two percent of the eﬃciency is increased,it is great energy save for hu-man.The development of small sized motor using bulk material has been domestically progressed by private companies for the golf-cart use.The R&D ac-tivities of it have been progressed in Germany,Russia andEngland.Fig.3Photograph of completed subset along with individual subcoil[5].Fig.4Cross section of the rotor[7]. 3..1Synchronous MotorThere are several type synchronous motor such as HTSﬁeld winding,HTS permanent magnet type,re-luctance type,and hysterisis type motor.Rockwell Automation and Reliance Electric(U.S.A.)studies air core AC synchronous machine with Bi-2223wire from1994.It operates at20∼40K cooled by closed Brayton cycle cryocooler.In phase II stage,R&D of HTS wire and coil,development of cooling system and veriﬁcation of1,000hp HTS motor[5].In Fig.3theﬁnal coil-set is shown.Its operating temperature is33K andﬁeld winding cur-rent is134A.Tampere University of Technology built a HTS synchronous machine of1.5kW and1500rpm as aﬁrst step in an attempt to develop electric machin-ery for special purposes such as ship propulsion[6]. The working temperature of the SC coils is chosen to20K,liquid hydrogen will be used for cooling. From May1996,Yonsei University(Korea)per-forms project of rotatingﬁeld winding synchronous motor with BSCCO tape rated220V and25A[7,8]. The rotor includes liquid nitrogen cryostat.The cross section of the rotor is shown in Fig. 4.Its operating condition were1800rpm,77∼85K,DC 4Aﬁeld current.Its output was450W.The team;Technical University Budapest and University of the Negev reported an experimental HTS synchronous machine[9].The machine is ex-Fig.5Longitudinal view of the model machine[9]. Fig.6Superconducting2pole reluctance motor[10].cited with NdFeB rare-earth permanent magnets on the rotor and BSCCO rod-shaped armature conduc-tors on the stator.The operating temperature is60∼64K.The cross-section of the machine is shown in Fig.5,which has4poles and2symmetrical phases.Superconducting reluctance motors(2poles and4 poles)with YBCO bulk material have been built and tested up to more than10kW at77K by Oswald Electromotoren GmbH et al.[10]as shown in Fig.6. Obtained maximum force density of6N/cm2exceeds the values of conventional asynchronus machines by a factor of four.A series of two pole hysteresis HTS motors with output power rating from1kW(50Hz)yo4kW (400Hz)was constructed and successfully tested by the cooperation of Moscow State Aviation Institute and Institut f¨u r Physikalische Hochtechnologie[11].A new class of motor/generator utilizes the mag-neticﬂux trapping capability of HTS by J.R.Hull et al.[12].The rotor consists of a cylindricalshell Fig.7Calculatedﬂux lines for inﬁnitely long prism of HTS array[12].Fig.8An illustration of the CD/NSWC motor witha cutaway view of its internal components[14].composed of HTS segments that act as trapped-ﬁeld magnets,magnetized in such a way that a dipole magneticﬁled is produced in the interior of the shell as shown in Fig.7.The motor is constructed from 32rectangular Y-Ba-Cu-O parallelepipeds measur-ing32mm×32mm×13mm and the c-axis in the short dimension.The operating temperature is not ﬁxed.3..2Homopolar MotorNaval Surface Warfare Center(U.S.A.)started ho-mopolar DC motor project in1992[13].The output power were122hp at28K(liquid neon)and320hp at4.2K(liquid helium)with Bi-2223and Bi-2212. With Bi2223HTS wire,the shaft power developed by the dc homopolar motor with its HTSﬁeld mag-net operating at a temperature of4.2K and a current of120A was125kW as shwon in Fi.8[14].This power was produced with an armature current of30 kA and a rotational speed of11700rpm.3..3Brushless DC MotorThere were many prototype reports as shown in Fig.9[13].IRC in Superconductivity starts bulk YBCO permanent magnet type motor project at Oc-tober1996.The project purpose is toﬁnd the design rule with bulk HTS magnet at77K.Fig.9Rotor of brushless DC trappedﬂux motor[13].4.Superconducting WireThe speciﬁcations of available HTS wire are not enough to apply the system as shown in Table2∼3.Many eﬀort to develop HTS wire should be done simultaneously with system study.If the J e=200 kA/cm2(overall J c)is achieved,the system design will be changed.Y-123PVD method samples show high J c such as J c=3,000kA/cm2for short sample and J c=300kA/cm2for1m length sample.5.ConclusionThe novel projects on HTS power machine are de-scribed.Many projects started in90th.Almost idea to apply superconducting machines was pro-posed and demonstrated.It is required a long period to develop system under proper pilots with feasibil-ity study.The collaboration between diﬀerentﬁeld scientists and engineers such as physicist,electric en-gineer,mechanical engineer and cryogenic engineer has been required.[References][1]T.Hoshino,I.Muta,K.H.Hussein:“Separate-ly-excited DC motor performances energized by photovoltaic power”,Proc.ICEM98,2,696–701 (1998)[2]New Energy and Industrial Technology De-velopment Organization(NEDO):“Report on the leading research and development for the generic technologies of AC superconducting power equipment”(1999)[3]S.K.Singh,D.W.Schrbarth,E.S.Ortoli,J.R.Repp,O.R.Christianseon,J.H.Parker,Jr.J.W.Carr,Jr.:“Conceptual design of a high temperature superconducting generator”,IEEE Trans.,AS-9,2,1237–1240(1999)[4]L.K.Kovalev,K.V.Ilyushin, A. ri-onoﬀ,K.L.Kovalev,V.T.Penkin,ri-onoﬀ:“Alternators which use htsc wire coils and bulk YBCO materials”,Proc.ICEC17,379–382 (1998)[5]D.Aized,B.B.Gamble,A.Sidi-Yekhle,J.P.Voccio,D.I.Driscoll,B.A.Shoykhet,B.X.Zhang:“Status of the1,000hp HTS motor de-velopment”,IEEE Trans.,AS-9,2,1197–1200 (1995)[6]R.Mikkonen,L.S¨o derlund,J.-T.Eriksson:“The design and construction of a1500W HTS superconducting synchronous machine”,IEEE Trans.,MAG-32,4,2377–2380(1996)[7]M.K.Song,W.K.Jang,Y.S.Yoon,C.W.Moon,G.W.Hong,S.J.Lee,T.K.Ko:“Sta-bility analysis of high-Tc superconductinjg tape through magneticﬁeld analysis of the high-Tc superconducting synchronous motor”,Proc.KI-ASC1st Conference’99,81–84(1999)[8]M.K.Song,Y.S.Yoon,W.K.Jang,T.K.Ko,G.W.Hong,I. B.Jang:“The design, manufacture and characteristic experiment of a small-scaled high-Tc superconducting synchro-nous motor”,IEEE Trans.,AS-9,2,1241–1244 (1999)[9]I.Vajda,A.Szalay,N.G¨o bl,V.Meerovich,V.Sokolovsky:“Requirements for the industrial application of superconducting rotating electri-cal machines”,IEEE Trans.,AS-9,2,1225–1228 (1999)[10]B.Oswald,M.Krone,M.S¨o ll,T.Straßer,J.Os-wald,K.-J.Best,W.Gawalek,L.Kovalev:“Su-perconducting reluctance motors with YBCO bulk material”,IEEE Trans.,AS-9,2,1201–1204(1999)[11]L.K.Kovalev,K.V.Ilushin,S.M.-A.Koneev,K.L.Kovalev,V.T.Penkin,V.N.Poltavets, W.Gawalek,T.Habiseuther,B.Oswald,L.-J.Best:“Hysterisis and reluctance electric ma-chines with bulk HTS rotor elements”,IEEE Trans.,AS-9,2,1261–1264(1999)[12]J.R.Hull,S.S.Gupta,J.R.Gaines:“Trap-ped-ﬂux internal-dipole superconducting motor /generator”,IEEE Trans.,AS-9,2,1229–1232 (1999)[13]A. D.Crapo,J. D.Lloyd:“Homopolar DCmotor and trappedﬂux brushless DC motor using high temperature superconductor mate-rials”,IEEE Trans.,MAG-27,2,2244–2247 (1991)[14]D.J.Waltman,M.J.Superczynski:“High-tem-perature superconducting magnet motor dem-onstration”,IEEE Trans.,AS-5,4,3532–3535 (1995)Table2Critical current density J c of Bi system wire (PIT method).year199219951998short sample53.76973.8100m class 6.627.827.81000m class—17.723.3unit:kA/cm2,at77K,selfﬁeldTable3Critical current density J c of Y system wire (metallic base).year199219951998short sample1301,1303,0001m class45160300unit:kA/cm2,at77K,selfﬁeld。