Theoretical Study on multi-band effect on the ferromagnetism of itinerant electrons

巡回电子铁磁性多能带效应的理论研究

• 批准号: 09640453
• 负责人: KUBO Kenn
• 金额: $ 1.34万
• 依托单位: University of Tsukuba
• 依托单位国家: 日本
• 项目类别: Grant-in-Aid for Scientific Research (C)
• 财政年份: 1997
• 资助国家: 日本
• 起止时间: 1997 至 1998
• 项目状态: 已结题
• 来源: https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-09640453/
• 关键词: ferromagnetism; itinerant electrons; multiple-band effect; Hurd's rule coupling; double exchange inter-action; Collossal magneto-resistance

1. We studied the 1D Hubbard model with two-fold orbital degeneracy by using density matrix renormalization group method, and obtained ground state phase diagram. We obtained perfectly ferromagnetic ground state for n<1, n=1 and n>1 where n denotes the electron density per site. The ferromagnetism for n<1 was shown to be fragile against chay the band dispersion, while that for n>1 is robust.2. We studied the doubly degenerate Habbard model in infinite dimensions by using the dynamical mean field theory, and to obtained ground stats place diagram. We obtained perfectly ferromagnetic ground state for n=1 and n>1 while we did not find ferromagnetic for n<1. We also found phase separation for n<similar or equal>1 and n<less than oFrom above results we established that the Hand's rule coupling which accompanies orbital degeneracy is quite effective in realizing ferromagnetism. Especially the so-called double-exchange mechanism stabilizes metallic ferromagnetism for n>1.3. We constructed a single-site approximation for the single particle Green's function in the double exchange model. By using this Green's function are calculated the magnetic susceptibility and the electrical conductivity.4. We obtained the ground state phase diagram of the double exchange model in infinite dimensions taking into account of full quantum effects of spins.

1.利用密度矩阵重整化群方法研究了具有二重轨道简并度的一维Hubbard模型，得到了基态相图。当n<1，n=1和n>1时，我们得到了理想的铁磁基态，其中n表示每格点的电子密度。当n<1时，铁磁性对能带色散的影响是脆弱的，而当n>1时，铁磁性对能带色散的影响是稳健的.利用动力学平均场理论研究了无限维双简并Habbard模型，得到了基态位置图。当n=1和n>1时，我们得到了理想的铁磁基态，而当n<1时，我们没有发现铁磁基态。我们还发现了当n &lt;<similar or equal>1和n&lt;0时的相分离。从上述结果我们确定了伴随轨道简并的Hand规则耦合在实现铁磁性方面是相当有效的。特别是所谓的双交换机制稳定了n&gt;1.3的金属铁磁性。我们构造了双交换模型中单粒子绿色函数的单格点近似。利用该绿色函数计算了磁化率和电导率.考虑自旋的全量子效应，得到了无限维双交换模型的基态相图。

项目成果

T.Momoi,K.Kubo: "Ferromagnetism in the Hubbard model with orbital degeneracy in infinite dimensions" Physical Review B. 58・2. R567-R570 (1998)

T.Momoi，K.Kubo：“无限维度轨道简并的哈伯德模型中的铁磁性”物理评论 B. 58・2（1998）

T. Momoi, H. Sakamoto and K. Kubo: "Magnetization plateau in a two-dimensional multi-spin exchange model"Physical Review B. 59・14. 9491-9499 (1999)

T. Momoi、H. Sakamoto 和 K. Kubo：“二维多自旋交换模型中的磁化平台”物理评论 B. 9491-9499 (1999)

K.Kubo,D.Edwards,A.Green,T.Momoi and H.Sakamoto: "Magnetism and Electronic States in Systems with Strong Hund Coupling" "Physics of Manganites" ed.by T.A.Kaplan and S.D.Mahanty Plenum Publishing.Co.N.Y.未定. (1999)

K. Kubo、D. Edwards、A. Green、T. Momoi 和 H. Sakamoto：“具有强 Hund 耦合的系统中的磁性和电子态”“锰酸盐物理学”，T. A. Kaplan 和 S. D. Mahanty Plenum Publishing.Co 编辑。纽约待定（1999）

K.Kubo, T.Momoi and K.Niki: "Possibility of a Chiral Phase Transition in Two-Dimensional ^3He Solid" Journal of Low Temperature Physics. 110・1/2. 339-344 (1997)

K.Kubo、T.Momoi 和 K.Niki：“二维 ^3He 固体中手性相变的可能性”《低温物理学杂志》110・1/2（1997 年）。

D.M.Edwards, A.C.M.Green and K.Kubo: "Electronic Structure and resistivity of the double exchange model" J.Phys, : Condens.Matter. (to bepublised). (1999)

D.M.Edwards、A.C.M.Green 和 K.Kubo：“双交换模型的电子结构和电阻率”J.Phys，：Condens.Matter。