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

作者：Sun Jian; Liu Yang; Song Yun^*

来源：Acta Physica Sinica, 2015, 64(24): 247101.

DOI：10.7498/aps.64.247101

• orbital-selective Mott transition
• dynamical mean-field theory
• two-orbital Hubbard model
• Hund's rule coupling

Using the dynamical mean field theory with Lanczos method as its impurity solver, we study the orbital-selective Mott transition (OSMT) in the two-orbital J model and Jz model. In the multi-orbital systems, the Mott metal-insulator transition occurs successively when the widths of the bands are different. As the narrow orbital becomes Mott insulator while the wide orbital is still in metallic phase, we find an orbital-selective Mott phase (OSMP). There are two different Hubbard models that are frequently used to describe the OSMT, which are named J model and Jz model, respectively. 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 Jz model.
We study the ratio of bandwidth W-2/W-1 on the OSMT by analyzing the results of the density of states and quasi-particle weight. Comparing the phase diagrams obtained from the J and Jz models with the Hund's rule coupling J (J(z)) = U/4, we find that the OSMP region of the J model is much larger than that of the Jz model when W-2/W-1 = 0 : 5 or W-2/W-1 = 0 : 2. When the ratio of bandwidth increases to W-2/W-1 = 0 : 8, the OSMP disappears completely in the Jz model. However in the J model, we can still find the OSMT but the area of the OSMP shrinks significantly. Therefore, 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 the phase diagrams for different Hund's rule couplings J(J(z)) = U/4 and J (J(z)) = U/2. We find that when the bandwidth W-2/W-1 >= 0 : 7, the OSMT disappears in Jz model in the case of either J(z) = U/4 or J(z) = U/2. However, the OSMP always exists in the J model if the bandwidths of the two orbitals are different, suggesting that the rotation invariances of the Hund's rule couplings can protect the OSMP. Therefore, one should be more careful when using the Jz model instead of the J model to study the OSMP.

• 出版日期2015-12-20
• 单位北京师范大学