Band Calculations on YbB12, SmB6 and CeNiSn
Band Calculations on YbB12, SmB6 and CeNiSn
复制标题
YbB12、SmB6 和 CeNiSn 的能带计算
DOI：
10.1143/ptps.108.19
复制
发表时间：
1992
影响因子：
--
通讯作者：
H. Harima
中科院分区：
文献类型：
--
作者：
A. Yanase;H. Harima
许多稀土元素和吖系元素化合物都是众所周知的具有大比热系数的重费米子系统或具有活化型能隙的价态涨落系统。能带计算是研究这些材料电子结构的一种有效方法，尽管多体效应还没有得到充分的考虑。如果电子和传导电子之间的杂化很大，则费米面是用局域密度近似(LDA)进行常规能带计算的结果。如果/-电子具有良好的局域化并且具有较大的磁矩，则费米面有望类似于非I标准物质的费米面。因此，在不能预期大质量的情况下，研究/-电子系统的电子结构对于了解/-电子在其基态中的作用是很重要的。对于具有能隙的化合物，需要用LDA的能带计算结果来回答杂化是否导致能隙的问题。SmB61>；和YbB1z2>；‘3>；都是价态涨落化合物，具有明显的能隙。CeNiSn是一种致密的近藤化合物，具有能隙形成。实验结果表明，这种间隙的存在是可能的。YbB12和SmB6的电阻率在低温下都有数量级的提高，而CeNiSn3个方向的电阻率在正交轴线的三个方向上最多在5K以下仅增大约4倍。因此，CeNiSn中的能隙可能具有不同的特性。化合物SmB6具有CaB6型晶体结构，空间群为Pm3m。具有这种结构的三价化合物LaB6、PrB6、NDB6和YB6是良好的金属，每个金属离子有一个传导电子，而二价化合物如CaB6和SrB6是绝缘体。用LDA计算CaB6的能带在简单立方布里渊区的X点的价带和导带之间有一个很小的直接间隙。能隙的大小为0.3 eV，与文献[1]提出的0.4 eV的实验值是合理的一致
Many rare earth and actinide compounds are well known as heavy fermion systems with a large specific heat coefficient or as valence fluctuation systems with an energy-gap of activation type. Band calculation is a powerful method for investigat ing the electronic structures of these materials, although many-body effects are not sufficiently contained. If hybridization between /-electrons and conduction electrons is large, the Fermi surfaces are .explained as a result of a conventional band calcula tion using the local density approximation (LDA). If /-electrons are well localized and have a large magnetic moment, the Fermi surfaces are expected to be similar to those of non-I reference materials. Therefore investigations for the electronic struc tures of /-electron systems, provided the heavy masses cannot be expected, are important to know the role of /-electrons in their ground states. For the compounds with an energy-gap, results of band calculations using LDA are needed to answer the question whether hybridization causes a gap or not. Both of SmB6 1 > and YbB1z 2 >' 3 > are known as valence fluctuation compounds with clear gap. CeNiSn is known as a dense Kondo compound with a formation of an energy-gap. 4 >' 5 > The existence of the gap is suggested in the experiments. The resistivity of YbB12 and SmB6 rise in low temperatures in order of magnitude, while the resistivity in the c-direction of CeNiSn becomes about only 4 times larger below 5 K at most in three directiQns of the orthorhombic axes. Therefore, the energy gap in CeNiSn may have different charac ter. The compound SmB6 has a CaB6 type crystal structure with the space 'group of Pm3m. Trivalent compounds with this structure such as LaB6, PrB6, NdB6 and YB6 are good metals with one conduction electron per metallic ion, while divalent com pounds such as CaB6 and SrB6 are insulator. The band calculation for CaB6 calcu lated with LDA gives a small direct gap between the valence and conduction bands at the X points in the simple cubic Brillouin zone. 6 > The magnitude of the energy gap is 0.3 eV, in reasonable agreement with the experimental value, 0.4 eV suggested by