Superconducting Transition Metal Borocarbides
Superconducting Transition Metal Borocarbides
复制标题
超导过渡金属硼碳化物
DOI：
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发表时间：
2001
期刊：
影响因子：
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通讯作者：
H. Eschrig
中科院分区：
文献类型：
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作者：
S. Drechsler;H. Rosner;S. Shulga;H. Eschrig
我们提出了一个概述的四元金属间化合物稀土过渡金属硼碳化物和相关的硼氮化物化合物的电子结构的选择性能的现有知识。计算出的高度各向异性费米表面表现出明显的相似性，如嵌套区域，但也显着的区别。来自费米面嵌套部分的电子影响超导态的几个性质。我们报告的理论计算，强调这些电子的超导机制的相关性。从总能量计算得到的ScNi2B2C的结构参数允许区分相互矛盾的实验结构报告。由于在确定电子结构的过渡金属组分的存在下的相关效应的重要性进行了讨论，比较带结构的计算结果与各种电子光谱，如X射线吸收光谱（XAS）。与XAS数据的良好协议表明，与铜酸盐超导体相比，相关效应的重要性较小。这些系统的热力学性质erg理论特别强调的上临界场Hc2（T）和比热。特别地，从微观上解释了高质量单晶、多晶样品YNiB2C2、LuNiB2C2以及混合系统Yi_xLuxNiB2C2在TT附近所观察到的反常的Hc2（T）正曲率。Hc2（T）及其在T附近的正曲率的值是这类样品的一般内禀量。这两个量随着无序度的增加而减少，从而提供了样品质量的直接测量。
We present an overview of the present knowledge of the electronic structure of selected properties of quaternary intermetallic rare earth transition metal borocarbides and related boronitride compounds. The calculated highly anisotropic Fermi surfaces exhibit clear similarities such as nested regions but also significant distinctions. Electrons from the nested parts of the Fermi surface affect several properties in the superconducting state. We report theoretical calculations which emphasize the relevance of these electrons to the mechanism of superconductivity. Structural parameters for ScNi2B2C derived from total energy calculation allow to discriminate conflicting experimental structural reports. The importance of correlation effects due to the presence of the transition metal component in determining the electronic structure is discussed comparing the band structure calculation results with various electronic spectroscopies such as X-ray absorption spectroscopy (XAS). The excellent agreement with the XAS data suggests a minor importance of correlation effects compared with the cuprate superconductors. Thermodynamic properties of these systems erg theory with special emphasis on the upper critical fieldH c 2 (T)and the specific heat. In particular, the unusual positive curvature ofH c 2 (T)near TTobserved for high-quality single crystals, polycrystalline samples of YNiB2C2, LuNiB2C2as well as to a somewhat reduced extent also for the mixed system Yi_x LuxNiB2C2is explained microscopically. The values ofH c 2(T) and of its positive curvature near T, are intrinsic quantities generic for such samples. Both quantities decrease with growing disorder and thus provide a direct measure of the sample quality.