Lanthanide Fermi surface studies

The study of Coulomb transitions is especially valuable in actinide metals and intermetallic compounds (McEwen et al. 1990, Osborn et al. 1990). Because of the greater radial extent of the 5f charge distribution, the actinide f electrons tend to hybridise more strongly with band electron states than their lanthanide counterparts. In a number of actinide metals, it is evident that the f electrons contribute to the cohesive energy through the formation of 5f bands, either by direct f-f overlap, as in a-uranium, or by hybridisation with conduction bands, as in URUj or URhj (Oguchi and Freeman 1986, Johansson et al. 1987). In these cases, relativistic band theory is successful in predicting lattice constants, photoemission and Fermi surfaces (Arko et al. 1985) provided the f states are included as itinerant. 

However, the Fermi surface depends sensitively on details of the E-k relation, and the determination of the Fermi surface demands a more precise calculation for the eigenvalues than that for the cohesive energy. Therefore, for studies of the Fermi surface, these linearized methods should be applied carefully. Errors originating from linearized approximations should be minimized. Nevertheless, the LAPW method is valuable for calculations of the electronic structure in lanthanide compounds with complex crystal structures, such as LaCufi. 

For studies of the Fermi surface in the lanthanide compounds, it is necessary to develop a reliable theoretical method in which hybridization of the 4f electrons with other electrons as well as the relativistic effect can be taken into account quantitatively. For that purpose, the relativistic APW method proposed by Loucks (1967) provides a good starting basis. Loucks derived his original method from the Dirac one-electron equation, which is a natural extension of Slater s non-relativistic APW method (Slater 1937). It proved to be a powerful method comparable to a relativistic KKR method (Onodera and Okazaki 1966, Takada 1966). Loucks method does not accocunt for the symmetrization of the wave functions by group theory, nor it is a self-consistent method. These shortcomings are serious limitations for calculations of the energy band structure in the lanthanide compounds. 

We found that the band theory worked fairly well for studies of the electronic structures in various lanthanide compounds. The energy band structures and the Fermi surfaces were clarified for many La compounds, and the theoretical results were used as a good starting point for understanding of the electronic structures of the Ce and other light lanthanide compounds, in which the 4f electrons are believed to be localized. Moreover,... 

It is the dialuminides for which there is the most direct Fermi surface data amongst the Laves phase materials dHvA measurements exist for CeAlj (Lonzarich 1988, Springford and Reinders 1988, Reinders and Springford 1989). The primary reason for interest in the dialuminides is that one may expect that there will be no direct f-f interaction and that the hybridization interactions will also be very weak lattice separations are well beyond the critical separation of the Hill plots and Al has no d orbitals to hybridize with the lanthanide or actinide f states. Consequently, heavy-lanthanide dialuminides have been studied as classic systems of crystal-field-split f states interacting through RKKY interactions. 

Vinokurova et al. (1981) with the help of experimental data of the de Haas-Van Alphen effect and model calculations studied the pressure influence on the Fermi surface of yttrium (heavy lanthanide metals have analogous Fermi surfaces). They foimd a decrease of the webbing thickness under pressure. 

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