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Competition between antiferromagnetic and charge order in the Hubbard-Holstein model

机译：Hubbard-Holstein模型中反铁磁与电荷序之间的竞争

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摘要

We study the competition between an instantaneous local Coulomb repulsion and a boson mediated retarded attraction, as described by the Hubbard-Holstein model. Restricting to the case of half-filling, the ground-state phase diagram and the transitions from antiferromagnetically ordered states to charge ordered states are analyzed. The calculations are based on the model in large dimensions, so that dynamical mean-field theory can be applied, and the associated impurity problem is solved using the numerical renormalization group method. The transition is found to occur when electron-electron coupling strength U and the induced interaction λ due to electron-phonon coupling approximately coincide, U approx= λ. We find a continuous transition for small coupling and large ω_0, and a discontinuous one for large coupling and/or small ω_0. We present results for the order parameters, the static expectation values for the electrons and phonons, and the corresponding spectral functions. They illustrate the different types of behavior to be seen near the transitions. Additionally, the quasipar-ticle properties are calculated in the normal state, which leads to a consistent interpretation of the low-energy excitations.
机译：如Hubbard-Holstein模型所述，我们研究了瞬时局部库仑排斥与玻色子介导的延迟吸引力之间的竞争。限于半填充的情况，分析了基态相位图以及从反铁磁有序状态到电荷有序状态的过渡。计算是基于大尺寸模型的，因此可以应用动态平均场理论，并使用数值重归一化群方法解决相关的杂质问题。发现当电子-电子耦合强度U和由于电子-声子耦合引起的感应相互作用λ大致重合，U近似=λ时，发生过渡。对于小耦合和大ω_0，我们发现了一个连续的过渡，对于大耦合和/或小ω_0，我们找到了一个不连续的过渡。我们给出了阶数参数，电子和声子的静态期望值以及相应的谱函数的结果。它们说明了要在过渡附近看到的不同类型的行为。此外，准粒子的性质是在正常状态下计算的，这导致了对低能激发的一致解释。

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