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

对某些超铀化合物的电子结构，特别是费米面的研究取得了新的结果：1.用考虑轨道极化效应的相对论自旋极化能带理论计算了反铁磁体NpRhGa_5的费米面和磁矩。该材料具有HoGoGa_5型晶体结构，基态磁矩沿着[110]方向排列，传播矢量q=[0，0，1/2]。结果表明，从计算中得到的费米面的形状很好地解释了由de Haas-van Alphen（dHvA）效应测量的频率分支的角度依赖性。此外，在Np位的磁矩的大小与中子散射的观测值一致。从这些计算结果可以清楚地看出NpRhGa_5的5 f电子是一个巡游磁电子。2.我们研究了没有自旋和轨道自由度的NpRhGa_5的5 f电子是否也具有巡游磁电子的性质。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。计算结果与观察到的dHvA频率分支定量一致。此外，如果考虑到由电子比热系数估算的增强因子，我们可以定量地比较回旋有效质量的理论值和实验值。3.在国际上首次成功地观测到了钚化合物PuIn_3的dHvA频率。用相对论能带理论计算的结果能够定量地说明dHvA频率分支的来源。这一结果表明，在Pu化合物中5 f电子也表现为巡游电子.

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.