Basic Research on Electronic Structure Theory in Magnetic Highly-Correlated Electron Systems

在一些超铀化合物，特别是其费米表面的电子结构研究中，获得了新的结果：利用包含轨道极化效应的相对论自旋极化带理论计算了反铁磁体NpRhGa_5的费米表面和磁矩。该材料具有hogoga_5型晶体结构，基态磁矩沿[110]方向排列，传播矢量q=[0,0,1/2]。结果证明，从计算中得到的费米表面的形状很好地解释了由德哈斯-范阿尔芬（dHvA）效应测量的频率分支的角依赖性。此外，在Np位置的磁矩大小与中子散射观测值一致。从这些计算结果可以清楚地看出，NpRhGa_5的5f电子是一个流动的磁性电子。我们研究了没有自旋和轨道自由度的非磁性Np化合物是否保持相同的性质。虽然几乎所有的Np化合物都是磁性的，但NpGe_3是少数非磁性化合物之一。用相对论手理论计算了NpGe_3的费米面。计算结果与观测到的dHvA频率分支数量一致。此外，如果考虑电子比热系数估计的增强因子，我们可以定量地比较回旋加速器有效质量的理论值和实验值。在世界上首次成功地观察到非磁性Pu化合物PuIn_3中的dHvA频率。用相对论能带理论计算得到的结果能够定量地说明所测dHvA频率分支的起源。这一成功表明，非磁性Pu化合物中的5f电子也表现为流动电子。

A renewed results related with electronic structure research on some transuranium compounds, especially their Fermi surfaces, were obtained :1.The Fermi surface and the magnetic moment in an antiferromagnet NpRhGa_5 were calculated using a relativistic spin-polarized band theory including an orbital polarization effect. This material has HoGoGa_5-type crystal structure, and the magnetic moments in the ground state are arranged along the [110] direction with a propagation vector q=[0,0,1/2]. It turned out that the shape of the Fermi surface obtained from the calculations well explains the angular dependence of the frequency branches measured by the de Haas-van Alphen (dHvA) effect. Moreover, the magnitude of the magnetic moment at the Np site is in agreement with the observed value by neutron scattering. It became clear from these calculated results to characterize the 5 f electrons of NpRhGa_5 as an itinerant magnetic electron.2.We investigated whether the same character is maintained to a nonmagnetic Np compound without a spin and an orbital degree of freedom. Although almost all Np compounds are magnetic, NpGe_3 is one of a few nonmagnetic compounds. The Fermi surface of NpGe_3 was calculated by relativistic hand theory. The calculated results give a quantitative agreement of the observed dHvA frequency branches. Furthermore, if an enhancement factor estimated by an electronic specific heat coefficient is taken into consideration, we can compare quantitatively the theoretical values with the experimental values for cyclotron effective mass.3.The first observation of a dHvA frequency in a nonmagnetic Pu compound PuIn_3 was successful in the world. The calculated result by a relativistic band theory was able to show an origin of the measured dHvA frequency branch quantitatively. This success suggested that 5 f electrons in nonmagnetic Pu compound also behave as an itinerant electron.