Walkup Daniel, Ghahari Fereshte, Gutiérrez Christopher, Watanabe Kenji, Taniguchi Takashi, Zhitenev Nikolai B, Stroscio Joseph A
Physical Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA.
Maryland NanoCenter, University of Maryland, College Park, Maryland 20742, USA.
Phys Rev B. 2020;101(3). doi: https://doi.org/10.1103/physrevb.101.035428.
Interacting and tunable quantum dots (QDs) have been extensively exploited in condensed matter physics and quantum information science. Using a low-temperature scanning tunneling microscope (STM), we both create and directly image a new type of coupled QD system in graphene, a highly interacting quantum relativistic system with tunable density. Using detailed scanning tunneling spectroscopy (STS) measurements, we show that Landau quantization inside a potential well enables novel electron confinement via the incompressible strips between partially filled Landau levels (LLs), forming isolated and concentric LL QDs. By changing the charge density and the magnetic field we can tune continuously between single- and double-concentric LL QD systems within the same potential well. In the concentric QD regime, single-electron charging peaks of the two dots intersect, displaying a characteristic avoidance pattern. At moderate fields, we observe an unconventional avoidance pattern that differs significantly from that observed in capacitively coupled double-QD systems. We find that we can reproduce in detail this anomalous avoidance pattern within the framework of the electrostatic double-QD model by replacing the capacitive interdot coupling with a phenomenological charge-counting system in which charges in the inner concentric dot are counted in the total charge of both islands. The emergence of such strange forms of interdot coupling in a single potential well, together with the ease of producing such charge pockets in graphene and other two-dimensional (2D) materials, reveals an intriguing testbed for the confinement of 2D electrons in customizable potentials.
相互作用且可调谐的量子点（QDs）已在凝聚态物理和量子信息科学中得到广泛应用。利用低温扫描隧道显微镜（STM），我们在石墨烯（一种具有可调密度的强相互作用量子相对论体系）中创建并直接成像了一种新型的耦合量子点系统。通过详细的扫描隧道谱（STS）测量，我们表明势阱内的朗道量子化通过部分填充的朗道能级（LLs）之间的不可压缩条带实现了新型电子限制，形成了孤立且同心的朗道能级量子点。通过改变电荷密度和磁场，我们可以在同一势阱内的单同心和双同心朗道能级量子点系统之间连续调谐。在同心量子点区域，两个量子点的单电子充电峰相交，呈现出特征性的回避模式。在中等磁场下，我们观察到一种非常规的回避模式，与电容耦合双量子点系统中观察到的模式有显著差异。我们发现，通过用一种现象学电荷计数系统取代电容性点间耦合，在静电双量子点模型框架内可以详细再现这种异常回避模式，其中内同心量子点中的电荷包含在两个岛的总电荷中。在单个势阱中出现这种奇特的点间耦合形式，以及在石墨烯和其他二维（2D）材料中易于产生此类电荷口袋，揭示了一个用于在可定制势中限制二维电子的有趣试验平台。
