External field control of a few-particle-bound states in double quantum dots

用扩散量子蒙特卡罗方法研究了有限势垒宽度垂直耦合量子点中两电子之间的自旋和电荷关联，并在Hubbard模型分析的基础上阐明了它们与势垒厚度和磁场的依赖机制。当势垒厚度增加时，相对于电子转移效应的电荷关联增强，大大抑制了同一量子点中的两电子占据几率，反铁磁自旋耦合的大小分两个阶段减小。通过施加磁场，既抑制了反铁磁自旋耦合，又抑制了同一量子点中的两电子占据几率。在点的横向约束较弱的情况下，增加磁场也可以引起基态的串联转换，并发生反铁磁耦合和铁磁耦合之间的自旋耦合交替。

We study both spin and charge correlations between two electrons in vertically coupled quantum dots with a finite well width using a diffusion quantum Monte Carlo method, and clarify mechanism of their dependences on both a barrier thickness and a magnetic field on the basis of analysis in the Hubbard model.When the barrier thickness increases, two-electron occupation probability in the same dot is suppressed drastically by enhanced charge correlation relative to electron transfer effect and the magnitude of the anti-ferromagnetic spin coupling decreases in two stages.By applying magnetic field, both the anti-ferromagnetic spin coupling and the two-electron occupation probability in the same dot are suppressed, being caused by enhanced intra-dot charge correlation.In the case of weak lateral confinement in dots, serial switching of the ground states can also be induced by increasing magnetic field and alternation of spin coupling between anti-ferromagnetic coupling and ferromagnetic coupling occurs.