论文标题
六边形石墨烯量子点真空的崩溃：紧密结合与平均场哈伯德模型之间的比较研究
Collapse of the vacuum in hexagonal graphene quantum dots: a comparative study between the tight-binding and the mean-field Hubbard models
论文作者
论文摘要
在本文中，我们对使用两种不同的杂质在存在的六角形石墨烯量子点（GQD）的电子，磁性和传输性能进行系统研究，并使用两种不同的杂质，使用两种不同的配置：（1）中央库仑电势和（2）带有带电的碳空位。紧密结合（TB）和半填充的扩展哈伯德模型是数值求解的，并相互比较，以揭示电子相互作用和系统大小的影响。数值结果指出，异地库仑排斥力导致临界耦合常数增加到$β_ {\ text {c}} $ = 0.6，以获得中央库仑电位。 $β$的这种临界值被发现与GQD大小无关，即使在存在电子电子相互作用的情况下，也反映了其通用性。此外，传输峰突然下降显示了从亚临界$β$ $ <$ <$ $ <$ <$ <$ <$ <$ <$ <$ <$ <text {c}} $过渡到超临界$β$β$ $β$ $> $β_ {\ text {c}}} $制度。另一方面，对于带正电荷的空缺，最低界面状态的崩溃发生在$β_ {\ text {c}} $ = 0.7的相互作用情况下。有趣的是，当空缺被亚批判性充电时，由裸碳空位引起的局部磁矩被完全淬灭，而电子中的山谷分布在两个方案中都持续存在。
In this paper, we perform a systematic study on the electronic, magnetic, and transport properties of the hexagonal graphene quantum dots (GQDs) with armchair edges in the presence of a charged impurity using two different configurations: (1) a central Coulomb potential and (2) a positively charged carbon vacancy. The tight binding (TB) and the half-filled extended Hubbard models are numerically solved and compared with each other in order to reveal the effect of electron interactions and system sizes. Numerical results point out that off-site Coulomb repulsion leads to an increase in the critical coupling constant to $β_{\text{c}}$ = 0.6 for a central Coulomb potential. This critical value of the $β$ is found to be independent of GQD size, reflecting its universality even in the presence of electron-electron interactions. In addition, a sudden downshift in the transmission peaks shows a clear signature of the transition from subcritical $β$ $<$ $β_{\text{c}}$ to supercritical $β$ $>$ $β_{\text{c}}$ regime. On the other hand, for a positively charged vacancy, the collapse of the lowest bound state occurs at $β_{\text{c}}$ = 0.7 for the interacting case. Interestingly, the local magnetic moment, induced by a bare carbon vacancy, is totally quenched when the vacancy is subcritically charged, whereas the valley splittings in electron and hole channels continue to exist in both regimes.
