金属型非晶态InSb膜的相变和超导电性

本文利用低温蒸发凝聚技术,第一次获得了金属型非晶态InSb膜,它形成的条件是凝聚底板的温度低于120K。金属型非晶态InSb膜在凝聚温度下发生自发的第一电导跃变,样品由类液非晶态弛豫到类点阵非晶态.当退火温度T_α达到200K左右时,发生结晶相变,即第二电导跃变,并在210K达到电导峰值,形成层状结构的结晶金属相。当T_α继续升高时,这个亚稳金属相逐渐转变成结晶半导体相。实验发现金属型非晶态InSb是个超导体,其超导T_c因底板温度的不同而改变;第二电导峰值对应的亚稳结晶金属相也是一个超导相,其T_c=4.18K;在由结晶金属相向结晶半导体相逐渐转交过程中,超导相的T_c逐渐降低,转变宽度△T_c显著增加,并在T_α达到某一温度以后出现超导相变反常。     

非晶态超导体的2△0/(kBTc)和声子谱参量

提出了能够很好地描述非过渡金属无序和非晶态超导体的2Δ₀/(k_BT_c)与声子谱参量之间关系的一个公式:2Δ₀(k_BT_c=4.95[1-(T₀<ω>^1/2)/A(1/(λω₀)+1/(20λ<ω>)+1/(20<ω>))]。计算了大量已知声子谱的非晶和无序超导体的能隙2Δ₀对T_c的比,结果表明在百分之几的范围内与实验值符合。指出了非过渡金属和合金的非晶态超导体,既可以是一个2Δ₀/(k_BT_c)值远大于BCS理论值(3.53)的强耦合超导体,也可以是一个2Δ₀/(k_BT_c)值比BCS理论值还要小得多的弱耦合超导体。 关键词：     

高T_c氧化物Bi_(1.4)Pb_(0.6)Sr_2Ca_2Cu_3O_y大块超导体的弱连结和弱钉扎性质

掺Pb的Bi_(1.4)Pb_(0.6)Sr_2Ca_2Cu_3O_y氧化物是一个以110K 超导相为主的高 T_c 超导体,其零电阻 T_c 为107.1K. dc Meissner 效应表明,110K 相占样品体积的8.2%,85K 相占1.6%.不同磁场下的排磁通(Meissher)效应,超导体所占体积上限和下限的比较,不同磁场和测量电流的 R(T)超导转变,表明了样品中存在着丰富的弱连结超导电性.研究了弱连结超导体的 H_(c2)(T).直流磁化和 I_c(B)特性结果表明,大块 Bi_(1.4)Pb_(0.6)Sr_2Ca_2Cu_3O_y,是个弱钉扎Ⅱ类超导体,它的 H_(cl)(77K)=25Oe,且磁化曲线中有两个峰.加热实验表明,当温度升高到355K 时,样品的正常态电阻增加,零电阻超导 T_c 从107.1K 退化到99.5K.     

ANISOTROPY OF CRITICAL CURRENT DENSITY IN c-AXIS ORIENTED EPITAXIAL YBa2Cu3O7-δ FILMS

The dependence of critical current density J_c on the angle α between the directions of the applied magnetic field H (which was rotated in the c-axis-I plane) and the in-plane current I was measured on a c-axis oriented epitaxial YBa₂Cu₃O_7-δ films at 81 K, with the magnetic field strength up to 6T. Analysis of the experimental results on the basis of the classical scaling law of pinning force shows that there exist simultaneously planar-pinning and volume-pinning mechanisms, and the contribution of volume pinning increases wish decreasing while that of the planar pinning decreases, We propose that the decrease of Lorentz-force-independent critical current density with increasing H for H∥I results from the suppression of superconductivity by the magnetic field, The fact that the contribution of volume pinning increases with decreasing α also arises from the suppression of superconductivity in CuO₂ plane by the magnetic field.     

强磁场技术进展

评述了强磁场技术的新进展：超导强磁场已达到２１Ｔ；４０Ｔ和４５Ｔ场强的混合磁体即将建成；用于脉冲强磁场磁体的导体材料和磁体增强技术也取得了进展．     

THERMALLY ACTIVATED HOPPING IN Dy1-xPrxBa2Cu3O7-δ SYSTEM

The temperature dependence of resistivity in Dy_1-xPr_xBa₂Cu₃O_7-δ system with x>0.6 was measured. The experimental results show that Pr substitution leads to the localization of mobile holes and such a localization is enhanced with increasing Pr concentration. The gradually enhancing of localization induces Anderson transitions one by one in this system, including the transition from the conduction by excitation of holes to the one by thermal activation hopping between localized states, the so called Anderson transition type-I, and the transition from nearest neighbor hopping (NNH) to variable range hopping (VRH), the Anderson transition type-II, and the Anderson transition type-lI from 3D to 2D.     

强磁场下的固体物理研究进展

强磁场下的物理研究是一个富有成果的研究领域，40T以下稳态强磁场的研制成功为固体物理研究提供了新的科学机遇。文章简要地介绍强磁场下某些固体物理，其中包括高温超导体的H－T相图和非费米液体行为，德哈斯（de Haas)效应和费米面性质，电子的Wigner结晶及其动力学行为，磁场诱导的相变（如绝缘体－金属和超导转变），多级磁有序，串级自旋密度波和大块材料中的量子霍尔效应等的实验研究的近期进展，希望以此引起人们对国内强磁场下物理研究的关注。     

YBa_2Cu_3O_7－δ超导薄膜J_c的角度关系

实验测量了在８１Ｋ温度和直到６Ｔ各种磁场下临界电流密度与角度θ（磁场与ａｂ面的夹角）的关系，实验结果与有关的物理模型的比较表明、有效质量模型能更好地描述我们的结果．