Ground state of two-electron quantum dots in single-valley materials like GaAs is always a spin singlet regardless of what the potential and interactions are.
This statement cannot be generalized to the multi-valley materials like $n$-doped Si.
Here we calculate numerically the spectrum of a two-electron Si quantum dot and show that the dot with the lateral size of several nm can have the spin triplet ground state which is impossible in the single-valley materials.
Predicted singlet-triplet level crossing in two-electron Si quantum dots can potentially establish the platform for quantum simulation of magnetic many body systems based on quantum dots.
We suggest several examples of such systems that open a way to controlled quantum simulations within the condensed matter setting.
Functional renormalization group approach to the singlet-triplet transition in quantum dots
利用泛函重整化群方法研究了具有两个不同轨道的量子点在Hund耦合作用下的零偏压输运性质。通过调节轨道态的能量分离，量子点可以被驱动通过单重态-三重态跃迁。我们的方法，Karrasch { \em et al}的方法的基础上，我们适用于自旋相关的相互作用，恢复的量子点输运性质的关键特性，很少的数值工作。我们目前的结果在附近的过渡和比较我们的结果与以前的数值重整化群的结果和预测的微扰重整化群的电导。
Exchange effects in spin polarized transport through carbon nanotube quantum dots
我们研究了弱耦合单壁碳纳米管量子点与自旋极化导线之间的线性和非线性输运。我们考虑有限长度和小直径的管，不仅向前散射贡献的库仑势，而且短程过程发挥了重要作用。特别是，它们诱导交换效应，导致电子填充物4 n +2要么自旋S=0的非简并基态，要么三重基态。在线性制度中，我们提出的电导的分析结果-为S=0和三重基态-并表明，外部磁场是至关重要的，以揭示自旋性质的基态。在非线性制度，我们显示的稳定性图，清楚地区分不同的基态。我们观察到一个负微分电导（NDC）效应在S=0的基态反平行铅磁化。在存在外部磁场的情况下，可以检测到自旋阻塞效应，再次导致两种基态的NDC效应。
Institute of Physics, M. Curie-Skłodowska University（玛丽亚·居里-斯可罗多夫斯卡大学物理研究所）；Department of General Education, Polish Air Force University（波兰空军大学普通教育部）；Institute of Spintronics and Quantum Information, Faculty of Physics and Astronomy, A. Mickiewicz University（亚当·密茨凯维奇大学物理与天文学学院自旋电子学与量子信息研究所）
