Garreis R, Knothe A, Tong C, Eich M, Gold C, Watanabe K, Taniguchi T, Fal'ko V, Ihn T, Ensslin K, Kurzmann A
ETH Zurich (Swiss Federal Institute of Technology in Zurich), 8093 Zurich, Switzerland.
National Graphene Institute, University of Manchester, Manchester M13 9PL, United Kingdom.
Phys Rev Lett. 2021 Apr 9;126(14):147703. doi: 10.1103/PhysRevLett.126.147703.
Transport measurements through a few-electron circular quantum dot in bilayer graphene display bunching of the conductance resonances in groups of four, eight, and twelve. This is in accordance with the spin and valley degeneracies in bilayer graphene and an additional threefold "minivalley degeneracy" caused by trigonal warping. For small electron numbers, implying a small dot size and a small displacement field, a two-dimensional s shell and then a p shell are successively filled with four and eight electrons, respectively. For electron numbers larger than 12, as the dot size and the displacement field increase, the single-particle ground state evolves into a threefold degenerate minivalley ground state. A transition between these regimes is observed in our measurements and can be described by band-structure calculations. Measurements in the magnetic field confirm Hund's second rule for spin filling of the quantum dot levels, emphasizing the importance of exchange interaction effects.
通过双层石墨烯中的少电子圆形量子点进行的输运测量显示，电导共振以四个、八个和十二个为一组出现聚束现象。这与双层石墨烯中的自旋和能谷简并性以及由三角翘曲引起的额外三重“小能谷简并性”相一致。对于少量电子，这意味着量子点尺寸小且位移场小，二维s壳层然后是p壳层分别依次被四个和八个电子填充。对于电子数大于12的情况，随着量子点尺寸和位移场增加，单粒子基态演变为三重简并的小能谷基态。在我们的测量中观察到了这些状态之间的转变，并且可以通过能带结构计算来描述。在磁场中的测量证实了量子点能级自旋填充的洪德第二规则，强调了交换相互作用效应的重要性。
