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arXiv 0907.3058cond-mat.str-el
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二维哈伯德模型中的赝能隙、非费米液体行为和粒子-空穴不对称性

Pseudogap, non-Fermi-liquid behavior, and particle-hole asymmetry in the 2D Hubbard model

Ansgar Liebsch, Ning-Hua Tong

摘要:

在有限温度精确对角化条件下,结合团簇动力学平均场论,研究了二维哈伯德模型中的掺杂效应。通过采用一个混合的基础,涉及集群网站和浴分子轨道的投影晶格格林函数到2x2集群,一个相当准确的描述的自能的低频特性实现比在一个纯网站图片。从费米液体的过渡到非费米液体的行为减少空穴掺杂的库仑能量,次近邻跳跃,和温度的函数进行了研究。特别地,与X =(pi,0)相关联的自能分量Sigma_X被示出为当空穴掺杂降低到临界值delta_c以下时表现出非费米液体行为的开始。然后,Sigma_X(omega)的虚部在E_F以上发展出集体模,其表现出明显的掺杂色散。相应地,Sigma_X(ω)的实部在E_F以上具有正斜率,从而导致随着系统接近Mott转变而增加的粒子-空穴不对称性。这一现象与电子态在E_F附近的光谱权重的去除以及赝能隙的打开是一致的,赝能隙的打开随掺杂的减少而增加。相图显示Δ_c = 0.15. 0.20各种系统参数。对于电子掺杂,σ_X(ω)的集体模和伴随的赝能隙位于费米能以下,这与从正好低于E_F的空穴态去除光谱权重一致。临界掺杂,标志着非费米液体行为的开始,是系统小于空穴掺杂。

英文摘要:

The effect of doping in the two-dimensional Hubbard model is studied within finite temperature exact diagonalization combined with cluster dynamical mean field theory. By employing a mixed basis involving cluster sites and bath molecular orbitals for the projection of the lattice Green's function onto 2x2 clusters, a considerably more accurate description of the low frequency properties of the self-energy is achieved than in a pure site picture. The transition from Fermi-liquid to non-Fermi-liquid behavior for decreasing hole doping is studied as a function of Coulomb energy, next-nearest neighbor hopping, and temperature. In particular, the self-energy component Sigma_X associated with X=(pi,0) is shown to exhibit an onset of non-Fermi-liquid behavior as the hole doping decreases below a critical value delta_c. The imaginary part of Sigma_X(omega) then develops a collective mode above E_F, which exhibits a distinct dispersion with doping. Accordingly, the real part of Sigma_X(omega) has a positive slope above E_F, giving rise to an increasing particle-hole asymmetry as the system approaches the Mott transition. This behavior is consistent with the removal of spectral weight from electron states close to E_F and the opening of a pseudogap which increases with decreasing doping. The phase diagram reveals that delta_c = 0.15 ... 0.20 for various system parameters. For electron doping, the collective mode of Sigma_X(omega) and the concomitant pseudogap are located below the Fermi energy which is consistent the removal of spectral weight from hole states just below E_F. The critical doping which marks the onset of non-Fermi-liquid behavior, is systematically smaller than for hole doping.

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