洪德耦合的调控与轨道选择Mott相变  

Manipulation of Hund's rule coupling and orbital-selective Mott transition

作　　者：孙健[1] 刘洋[1] 宋筠[1] 

机构地区：[1]f北京师范大学物理系,北京100875

出　　处：《物理学报》2015年第24期280-288,共9页Acta Physica Sinica

基　　金：国家自然科学基金(批准号:11174036,11474023);国家重点基础研究发展计划(批准号:2011CBA00108);中央高校基本科研业务费资助的课题~~

摘　　要：洪德耦合相互作用是导致多轨道体系发生轨道选择Mott相变的重要因素之一.通过调控洪德耦合相互作用来研究其不同组成部分对轨道选择Mott相变的作用.利用基于Lanczos求解器的动力学平均场理论,对比了双轨道的J模型和J_z模型的金属-绝缘体相变,并重点讨论洪德耦合中的自旋翻转项和电子对跃迁项以及轨道宽度比值W_2/W_1如何影响轨道选择Mott相变.在J模型的相图中,Mott选择相占有较大的区域,而J_z模型的轨道选择Mott相只存在于一个很狭窄的区域内,这说明自旋翻转项及电子对跳跃项是有利于轨道选择Mott相变发生的关键因素.此外当轨道宽度之比大于W_2/W_1=0.7时,J_z模型的轨道选择Mott相会完全消失,而J模型中只要轨道宽度不同都存在轨道选择Mott相.因而,简化后的J_z模型只是在特定条件下才适合于研究轨道选择Mott相变.Using the dynamical mean field theory with Lanczos method as its impurity solver, we study the orbital-selectiv Mott transition（OSMT） in the two-orbital J model and Jz model. In the multi-orbital systems, the Mott metal-insulato transition occurs successively when the widths of the bands are different. As the narrow orbital becomes Mott insulato while the wide orbital is still in metallic phase, we find an orbital-selective Mott phase（OSMP）. There are two differen Hubbard models that are frequently used to describe the OSMT, which are named J model and Jz model, respectivel The J Model is composed of the whole Hund＇s rule coupling terms, including the spin-flip term, the pair-hopping term and the Ising type Hund＇s rule coupling term. However, there is only Ising type Hund＇s rule coupling term in the J model.We study the ratio of bandwidth W2/W1 on the OSMT by analyzing the results of the density of states an quasi-particle weight. Comparing the phase diagrams obtained from the J and Jz models with the Hund＇s rule couplin J（Jz） = U /4, we find that the OSMP region of the J model is much larger than that of the Jz model when W2/W1 = 0or W2/W1 = 0.2. When the ratio of bandwidth increases to W2/W1 = 0.8, the OSMP disappears completely in the J model. However in the J model, we can still find the OSMT but the area of the OSMP shrinks significantly. Therefor the OSMT happens more easily in the J model than in the Jz model.In order to discuss the cooperative effect of the bandwidth and Hund＇s rule coupling on the OSMT, we compare th phase diagrams for different Hund＇s rule couplings J（Jz） = U /4 and J（Jz） = U /2. We find that when the bandwidt W2/W1〉 0.7, the OSMT disappears in Jz model in the case of either Jz= U /4 or Jz= U /2. However, the OSM always exists in the J model if the bandwidths of the two orbitals are different, suggesting that the rotation invariance of the Hund＇s rule couplings can protect the OSMP. Therefore, one should be more careful when using the Jz mod instead o

关 键 词：轨道选择Mott相变 动力学平均场理论 双轨道Hubbard模型 洪德耦合 

分 类 号：O469[理学—凝聚态物理]