锯齿形窄石墨烯纳米带中的纠缠、激发和关联效应
Entanglement, excitations and correlation effects in narrow zigzag graphene nanoribbons
摘要：
我们研究了锯齿形窄边石墨烯纳米带的激发光谱和基态性质。最近已经合成了具有可比宽度的纳米带[P.Ruffieux，\emph{et al.} Nature \textbf{531}，489（2016）]，并且它们的描述需要更复杂的方法，因为在这种情况下，常规方法，如平均场或具有局部密度近似的密度泛函理论，无法捕获增强的量子涨落。利用无偏密度矩阵重整化群算法计算了不同宽度和相互作用强度下的电荷带隙，并与平均场结果进行了比较。事实证明，在前一种情况下，由于对量子涨落的适当处理，带隙要小得多。应用量子信息理论的基本原理，我们还揭示了带内的纠缠结构，并检查子系统密度矩阵的频谱，以了解纠缠的起源。我们研究了磁有序的可能性和磁场的影响。我们的研究结果是相关的理解在不同的最近的实验中的间隙值和它们之间的偏差。
英文摘要：
We investigate the low-lying excitation spectrum and ground-state properties of narrow graphene nanoribbons with zigzag edge configurations. Nanoribbons of comparable widths have been synthesized very recently [P. Ruffieux, \emph{et al.} Nature \textbf{531}, 489 (2016)], and their descriptions require more sophisticated methods since in this regime conventional methods, like mean-field or density-functional theory with local density approximation, fail to capture the enhanced quantum fluctuations. Using the unbiased density-matrix renormalization group algorithm we calculate the charge gaps with high accuracy for different widths and interaction strengths and compare them with mean-field results. It turns out that the gaps are much smaller in the former case due to the proper treatment of quantum fluctuations. Applying the elements of quantum information theory we also reveal the entanglement structure inside a ribbon and examine the spectrum of subsystem density matrices to understand the origin of entanglement. We examine the possibility of magnetic ordering and the effect of magnetic field. Our findings are relevant for understanding the gap values in different recent experiments and the deviations between them.
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