Electronic states and the Fermi surface in f-electron compounds

重电子化合物中f电子的性质最近已被能带理论很好地阐明。特别地，在4f电子的巡游电子模型的基础上，用相对论能带理论很好地解释了CeSn_3的费米面的形状，而不考虑回旋有效质量。这意味着在顺磁Ce化合物中，它们可能在基态是巡回的，并直接有助于费米面的形成。本计画的主要目的是确认Ce化合物和U化合物中f电子的能带图像。首先，计算了CeNi和CeRu_2Si_2两种顺磁化合物的费米面，并与最近的deHaas-van Alphen（dHvA）效应实验进行了比较。我们发现一个合理的理论和实验之间的良好协议，从而使4f电子的能带图片的有效性更加健全。其次，计算了LaRu_2Ge_2的费米面，并与铁磁化合物CeRu_2Ge_2的dHvA效应实验进行了比较。用LaRu_2Ge_2的费米面几乎完全解释了实验结果。这一结果表明，4f电子在CeRu_2Ge_2中是局域化的，对费米面几乎没有影响。第三，计算了UB_1的费米面，并<12>与dHvA效应实验进行了比较。在UB_中<12>，dHvA频率的幅度和角度依赖性都得到了合理的解释。此外，回旋质量和电子比热系数也能得到很好的定量解释。在该化合物中，5 f电子通过与B 2 p电子的强杂化而巡游。对CeRh_2，UGe_2和PuX（X为S，Se和Te）进行了初步计算。

A nature of the f electrons in the heavy-electron compound has recently been clarified well by band theory. In particular, on the basis of an itinerant-electron model for the 4f electrons, the shape of the Fermi surface of CeSn_3, apart from the cyclotron effective mass, is well explained by a relativistic band theory. It means that in paramagnetic Ce compounds they may be itinerant in the ground state and contribute directly to the formation of the Fermi surface. It is a main purpose of this project to confirm an energy band picture for the f electrons in the Ce compounds and the U compounds. Firstly, the Fermi surface is calculated for the two paramagnetic compounds CeNi and CeRu_2Si_2 and compared with the recent de Haas-van Alphen(dHvA) efeect experiments. We find a reasonably good agreement between theory and experiment and thus make the validity of an energy band picture for the 4f electrons more sound. Secondly, the Fermi surface is calculated for LaRu_2Ge_2 and compared with the dHvA effect experiment for the ferromagnetic compound CeRu_2Ge_2. The experimental result is explained almost perfectly by using the Fermi surface of LaRu_2Ge_2 without any modifications. This result implies that the 4f electrons are localized and scarcely influence the Fermi surface in CeRu_2Ge_2. Thirdly, the Fermi surface is calculated for UB_<12> and compared with the dHvA effect experiment. In UB_<12>, both the magnitude and the angle dependence of the dHvA frequencies is explained reasonably well. In addition, the cyclotron masses as well as the electronic specific heat coefficient can be explained quantitatively well. In this compound, the 5f electrons are itinerant through a strong hybridization with the B 2p electrons. Preliminary calculations are carried out for CeRh_2, UGe_2 and PuX, where X means S, Se and Te.