Electronic states and the Fermi surface in f-electron compounds

最近用能带理论很好地阐明了重电子化合物中f电子的一个性质。特别是在4f电子的巡回电子模型的基础上，用相对论能带理论很好地解释了CeSn3费米面的形状，而不考虑回旋有效质量。这意味着在顺磁性Ce化合物中，它们可能在基态中巡游，并直接对费米面的形成做出贡献。本项目的一个主要目的是确定Ce化合物和U化合物中f电子的能带图。首先，计算了两种顺磁性化合物CeNi和CeU_2Si_2的费米面，并与最近的De Haas-van Alphen(DHvA)实验进行了比较。我们发现理论和实验之间有相当好的一致性，从而使4f电子能带图的有效性更加合理。其次，计算了LaRu_2Ge_2的费米面，并与铁磁性化合物CeU_2Ge_2的dHvA效应实验进行了比较。未作任何修改，用LaRu_2Ge_2的费米面对实验结果进行了较好的解释。这一结果表明，在CeU_2Ge_2中，4f电子是局域化的，对费米面几乎没有影响。第三，计算了UB_lt；12&gt；的费米面，并与dHvA效应实验进行了比较。在UB_&lt；12&gt；中，dHvA频率的大小和角度的关系都得到了很好的解释。此外，回旋加速器的质量和电子比热系数也可以很好地定量解释。在该化合物中，5f电子通过与B2p电子的强杂化而巡游。对CeRh_2、UGe_2和PUX进行了初步计算，其中X表示S、Se和Te。

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.