Institut für Theoretische Physik und Astrophysik, Universität Würzburg, Germany.
J Phys Condens Matter. 2013 Jan 9;25(1):014005. doi: 10.1088/0953-8984/25/1/014005. Epub 2012 Dec 5.
We use continuous-time quantum Monte Carlo simulations to study retardation effects in the metallic, quarter-filled Holstein model in one dimension. Based on results which include the one- and two-particle spectral functions as well as the optical conductivity, we conclude that with increasing phonon frequency the ground state evolves from one with dominant diagonal order-2k(F) charge correlations-to one with dominant off-diagonal fluctuations, namely s-wave pairing correlations. In the parameter range of this crossover, our numerical results support the existence of a spin gap for all phonon frequencies. The crossover can hence be interpreted in terms of preformed pairs corresponding to bipolarons, which are essentially localized in the Peierls phase, and 'condense' with increasing phonon frequency to generate dominant pairing correlations.
我们使用连续时间量子蒙特卡罗模拟研究了一维金属、四分之一填充的 Holstein 模型中的延迟效应。基于包括单粒子和双粒子谱函数以及光导率在内的结果，我们得出结论，随着声子频率的增加，基态从具有主导对角序-2k(F)电荷相关的状态演变为具有主导非对角涨落的状态，即 s 波配对相关。在这个交叉区域的参数范围内，我们的数值结果支持所有声子频率下都存在自旋能隙。因此，这个交叉可以用对应双极化子的预形成对来解释，双极化子本质上是局域在 Peierls 相中，并且随着声子频率的增加而“凝聚”，从而产生主导的配对相关。
