Superconductivity in diamond

Diamond is an electrical insulator well known for its exceptional hardness. It also conducts heat even more effectively than copper, and can withstand very high electric fields. With these physical properties, diamond is attractive for electronic applications, particularly when charge carriers are introduced (by chemical doping) into the system. Boron has one less electron than carbon and, because of its small atomic radius, boron is relatively easily incorporated into diamond; as boron acts as a charge acceptor, the resulting diamond is effectively hole-doped. Here we report the discovery of superconductivity in boron-doped diamond synthesized at high pressure (nearly 100,000 atmospheres) and temperature (2,500-2,800 K). Electrical resistivity, magnetic susceptibility, specific heat and field-dependent resistance measurements show that boron-doped diamond is a bulk, type-II superconductor below the superconducting transition temperature T(c) approximately 4 K; superconductivity survives in a magnetic field up to Hc2(0) > or = 3.5 T. The discovery of superconductivity in diamond-structured carbon suggests that Si and Ge, which also form in the diamond structure, may similarly exhibit superconductivity under the appropriate conditions.     

微尺度重掺杂硅光栅波长选择性吸收率的数值研究

利用时域有限差分法对中红外波段微尺度重掺杂硅简易光栅和复杂光栅的光谱吸收率进行数值模拟,验证重掺杂硅复杂光栅作为波长选择性吸收表面的可行性.计算结果表明;对于简易光栅,不同填充比条件下的光谱吸收率曲线均存在峰值,其中填充比为0.4的吸收率峰值远高于填充比为0.1的峰值;随着光栅周期的增大,吸收率峰值位置向长波长波段移动;当掺杂浓度增加时,吸收率峰值位置移向短波长波段并且半峰全宽值有所减小.对于复杂光栅,与简易光栅相比虽然吸收率峰值有所降低,但其半峰全宽明显比简易光栅的大,主要来源于表面等离子体激元的激发.作为波长选择性吸收表面,复杂光栅表现出比简易光栅更优良的性能.     

Superconductivity in MgB2

In January of 2001 the superconductivity of the compound MgB2 with a critical temperature Tc of up to 39 K was discovered. This Tc is the highest in all intermetallic compound and alloy superconductors. MgB2 has a simple structure and its manufacturing capital cost is lower, therefore it could become a practical superconductor in the future. The recent progress is reviewed here which covers the progress in electronic structure, high Tc mechanism, superconducting parameters (Debye temperature, specific heat coefficient of electron, critical fields, coherent length, penetration depth, energy gap, critical current and relaxation rate of flux). Moreover the issue on power transmission is discussed.     

Superconductivity without phonons

The idea of superconductivity without the mediating role of lattice vibrations (phonons) has a long history. It was realized soon after the publication of the Bardeen-Cooper-Schrieffer (BCS) theory of superconductivity 50 years ago that a full treatment of both the charge and spin degrees of freedom of the electron predicts the existence of attractive components of the effective interaction between electrons even in the absence of lattice vibrations--a particular example is the effective interaction that depends on the relative spins of the electrons. Such attraction without phonons can lead to electronic pairing and to unconventional forms of superconductivity that can be much more sensitive than traditional (BCS) superconductivity to the precise details of the crystal structure and to the electronic and magnetic properties of a material.     

超导修订版

在1986-1987年发现高温超导后的几年里，人们对超导抱有很大的期望。本书第一版写于1989年，那时，对高温超导有很高的热情。2004年本书出版第二版时，已经很清楚认识到，对高温超导广泛应用的希望值有点高了。但是，超导的应用前景仍然是巨大的，而且一般的低温超导比新的高温超导应用更广。本书的重点是介绍高温超导的机理和制造方法。     

排斥型有效互作用下的超导电性

分析了电子间在有效排斥互作用下的超导电性．发现当能带宽度Ｗ＞Ｅｃ，ｏ（）时，存在电子对；当Ｗ＜Ｅｃ，ｏ时，电子对消失．从而认为在电子对消失的区域，描写超导电性的应该是某种准粒子对，而不是电子对．     

Mg掺杂硅团簇MgSin(n=1~10)的结构和电子性质研究

运用杂化密度泛函B3LYP理论方法,在6-311+G(d,p)基组水平上对MgSin(n=1~10)多种低能异构体进行优化,获得了各个尺寸下团簇的最低能量结构,并研究MgSin(n=1~10)的结构特点和电子性质.结果表明单个镁原子掺杂硅可得到稳定的二元掺杂团簇.     

铈掺杂氮化硅电子结构及其光学性能的第一性原理

采用密度泛函理论下的平面波赝势方法和广义梯度近似,计算稀土元素铈掺杂氮化硅体系的电子结构及其光学性能.结果表明:随掺杂浓度的提高,能带密度逐渐增加,带隙逐渐减小,分别为1.609、1.117、0.655eV,接近半导体带隙特征;差分电荷密度图表明,随掺杂浓度的提高,铈与氮成键的共价性逐渐降低,离子性逐渐升高,并通过布居值得到验证;掺杂一个铈原子体系在低能区的介电常数和损耗较小,表明其作为电介质材料在光电器件应用中可体现较长的使用寿命,同时在可见光区具有低的吸收系数和反射率,呈现"透明型"性质,说明光在该体系中更容易传播,也表明其作为光学元件具有潜在的应用前景.     

Tl—Ca—Ba—Cu—O体系的高温超导电性及其物相

用TlNO_3在Tl-Ca-Ba-Cu-O体系中获得了超导转变温度120K以上、零电阻温度为108K的超导体。超导相可以用Z.Z.Sheng报道的2122相指标,其晶格常数是a=5.450A,b=5.447A,c=29.57A。     

MgB2薄膜的超导电性

采用平面波赝势方法计算了MgB2超导薄膜的电子结构.结果发现,表面层B(S)在费米能级处的态密度显著增强.在线性响应的密度泛函微扰理论框架下计算了MgB2薄膜的动力学性质及电-声子相互作用,分析了MgB2超导薄膜在Γ点的振动模的频率.结果发现,MgB2薄膜中的声子存在软化现象,并且声子的软化提高了电-声子相互作用,从而增强了薄膜的超导电性.     

Superconductivity in two-dimensional CoO2 layers

Since the discovery of high-transition-temperature (high-T(c)) superconductivity in layered copper oxides, many researchers have searched for similar behaviour in other layered metal oxides involving 3d-transition metals, such as cobalt and nickel. Such attempts have so far failed, with the result that the copper oxide layer is thought to be essential for superconductivity. Here we report that Na(x)CoO2*yH2O (x approximately 0.35, y approximately 1.3) is a superconductor with a T(c) of about 5 K. This compound consists of two-dimensional CoO2 layers separated by a thick insulating layer of Na+ ions and H2O molecules. There is a marked resemblance in superconducting properties between the present material and high-T(c) copper oxides, suggesting that the two systems have similar underlying physics.     

Superconductivity from buckled-honeycomb-vacancy ordering

Vacancies are prevalent and versatile in solid-state physics and materials science.The role of vacancies in strongly correlated materials,however,remains uncult...     

过渡金属掺杂的立方型ZrO_2催化剂处理含酚废水

采用共沉淀法制备了一系列过渡金属(Cu,Mn,Co,Fe,Ni,Cr)掺杂的ZrO2催化剂,XRD表征.表明属于立方型ZrO2结构.在250 mL间歇式反应釜中,反应温度150℃,初始压力为3.5 MPa,反应时间90 min的条件下,对苯酚(2.1 g/L,COD质量浓度为5 000 mg/L)的催化湿式氧化结果为:COD去除率为12.6%~83.1%.其催化活性顺序为:Cu-ZrO2>Mn-ZrO2>Co-ZrO2>Ni-ZrO2>Cr-ZrO2>Fe-ZrO2.研究了催化剂Cu-ZrO2在不同反应条件下对COD去除率的影响.     

介观尺度超导体的超导电性

在 Ginzburg-Landau 理论框架内,发展了一种解析的处理方法研究了介观超导体的超导电性。     

Superconductivity at 39 K in magnesium diboride

In the light of the tremendous progress that has been made in raising the transition temperature of the copper oxide superconductors (for a review, see ref. 1), it is natural to wonder how high the transition temperature, Tc, can be pushed in other classes of materials. At present, the highest reported values of Tc for non-copper-oxide bulk superconductivity are 33 K in electron-doped Cs(x)Rb(y)C60 (ref. 2), and 30 K in Ba(1-x)K(x)BiO3 (ref. 3). (Hole-doped C60 was recently found to be superconducting with a Tc as high as 52 K, although the nature of the experiment meant that the supercurrents were confined to the surface of the C60 crystal, rather than probing the bulk.) Here we report the discovery of bulk superconductivity in magnesium diboride, MgB2. Magnetization and resistivity measurements establish a transition temperature of 39 K, which we believe to be the highest yet determined for a non-copper-oxide bulk superconductor.     

Bi—Sr—Ca—Cu—O系超导电性的探讨

用固态反应法制备不含稀土元类的BiSrCaCu_2Oy陶瓷高温超导体。该系统可能存在多个高温超导相,不同工艺可改变各超导相成份;150K附近可能有一更高温超导相。