In this last of three articles on the optical absorption of electrons in ahalf-filled Peierls-distorted chain we address the dimerized extended Hubbardmodel in the limit of a large on-site interaction $U$. When the Hubbardinteraction is large both compared to the band width $W$ and the nearestneighbor interaction $V$ the charge dynamics is properly described by theHarris-Lange model. This model can be exactly mapped onto a model of freespinless Fermions in parallel (Hubbard-)bands of width $W$ which are eventuallyPeierls-split. To determine the coherent absorption features at lowtemperatures we design and employ the ``no-recoil approximation'' in which weassume that the momentum transfer to the spin degrees of freedom can only be$\Delta q_S=0$ or $\Delta q_S=\pi/a$ during an optical excitation. We presentexplicit analytical results for the optical absorption in the presence of alattice dimerization $\delta$ and a nearest-neighbor interaction $V$ for theN\'{e}el and dimer state. We find that the coherent part of the opticalabsorption for $V=0$ is given by a single peak at $\omega=U$ and broad but weakabsorption bands for $W\delta\leq |\omega-U| \leq W$. The central peak at$\omega=U$ only vanishes for $\delta=0$ in the N\'{e}el state. For anappreciable nearest neighbor interaction $V>W/2$ almost all spectral weight istransferred to the $\Delta q_C=0$-exciton and the $\Delta q_C=\pi/a$-excitonwhose relative spectral weights very sensitively depend on both the lattice andthe spin dimerization of the ground state.
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机译:在有关半充满的Peierls扭曲链中电子的光吸收的三篇文章的最后一篇中,我们讨论了在大型现场相互作用$ U $的限制下二聚化扩展的Hubbardmodel。当Hubbard交互作用较大时,与带宽$ W $和最近邻交互作用$ V $相比,电荷动力学由Harris-Lange模型正确描述。该模型可以精确地映射到最终以皮埃尔斯分裂的,平行的(Hubbard-)带$ W $的自由旋转费米子模型。为了确定低温下的相干吸收特征,我们设计并采用了``无反冲近似'',其中假设将动量传递给自旋自由度只能是$ \ Delta q_S = 0 $或$ \ Delta q_S = \ pi / a $在光激发过程中。我们给出了存在格子二聚化$ \ delta和N \'{e} el和二聚体状态的最近邻相互作用$ V $时光吸收的明确分析结果。我们发现$ V = 0 $的光吸收的相干部分由$ \ omega = U $的单个峰和$ W \ delta \ leq | \ omega-U |的宽而弱的吸收带给出。 \ leq W $。 $ \ omega = U $的中心峰在N \'{e} el状态仅消失$ \ delta = 0 $。对于明显的最近邻居交互$ V> W / 2 $,几乎所有频谱权重都转移到$ \ Delta q_C = 0 $ -exciton和$ \ Delta q_C = \ pi / a $ -exciton,其相对频谱权重非常依赖于两者晶格和基态的自旋二聚化。
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