原子簇La_(8-x)Ba_xCuO_6的原子磁矩和自旋极化的电子结构研究  

Study on the spin-polarized electronic structures and atomic magnetic moments of cluster La_(8-x)Ba_xCuO_6

作　　者：陈丽[1] 李华[1] 董建敏[1] 潘凤春[1] 梅良模[1] 

机构地区：[1]山东大学物理与微电子学院

出　　处：《物理学报》2004年第1期254-259,共6页Acta Physica Sinica

基　　金：国家 8 63计划项目 (批准号 :2 0 0 2AA3 2 40 5 0 );国家自然科学基金 (批准号 :5 99710 2 6)资助的课题~~

摘　　要：利用MS Xα方法研究了化合物La2 -yBayCuO4 的原子磁矩和自旋极化的电子结构 .理论计算得到母相氧化物La2 CuO4 的Cu原子磁矩为 0 37μB,与实验值 0 4 8± 0 15 μB 基本一致 .研究结果显示 ,由于Ba原子对部分La的替代 ,使构成化合物的基本原子簇La8-xBaxCuO6 的点群对称性降低 ,分子轨道简并度解除 ,轨道杂化效应增强 ,减弱了氧化物的 (准 )二维特性 ,导致Cu O层与其近邻原子层的耦合增强 ,因此影响了原子层间的电荷迁移方向 ,对Cu O层中载流子的性质有重要影响 .由于Ba掺杂在化合物中产生的空穴 ,不仅进入O格点 ,也同时进入Cu格点 ,对Cu O层上Cu和O原子价态、磁矩以及电子态密度分布有重要影响 .研究结果认为 ,由于掺杂产生的空穴对化合物超导电性的影响具有两面性 :初期掺杂有利于产生超导电性 ;当掺杂较多时抑制超导电性 .这是导致La2 14体系的超导转变温度Tc 随掺杂量y的变化 (即Tc y拱形曲线 )的一个重要原因 .The X α method is applied to study the spin-polarized electronic structures and atomic magnetic moments of clusters La 8-x Ba xCuO 6 in the compound La 2-y Ba yCuO 4.This paper shows that Cu magnetic moment in La 2CuO 4 is 0 37 μ B, which is in better agreement with the experimental value(0 48±0 15 μ B). Ba substitution lowers the structure symmetry, removes molecular orbital degeneracy, and hence strengthens orbital hybridization and weakens quasi-two-dimensional feature, which enhance the coupling between Cu-O layer and the neighbormg layers and influence the charge transfer. These changes strongly affect the properties of carriers. Holes are introduced due to Ba substitution and they mainly enter into O sites, a few d-electronic holes enter into Cu sites, which causes important effects on the density of states, atomic magnetic moment and valence states of Cu and O in Cu-O layers. The results confirm that the holes are not always beneficial to the superconductivity. At the beginning the holes are beneficial to the superconductivity; they can decrease the superconductivity when more holes are introduced. This paper can explain that the transition temperature of high-temperature superconductive oxides changes with the variation of the doping level.

关 键 词：电子结构 自旋极化 原子磁矩 态密度 超导电性 钡原子 镧原子 轨道杂化效应 轨道简并度 点群对称性 

分 类 号：O562[理学—原子与分子物理]