Collaborative Research: Combined transport and scanning probe study of twisted van der Waals devices

许多半导体器件依赖于创建由多层组成的异质结构来实现其所需的功能。传统的半导体异质结构由于不同层之间的晶格匹配要求，在材料的选择上受到限制。然而，原子薄材料有能力克服这一限制，通过逐层堆叠方法实现范德华异质结构的创建。这将允许在这些异质结构中创建更广泛的电子特性。此外，它们还有一个额外的自由度，即不同层之间的扭转角，这就产生了层之间的长波波纹图案。这种波纹模式可以调节电子特性，并可以产生相关状态，如超导或磁性。在这个项目中，我们将使用MX2形式的半导体过渡金属二硫族化合物，其中M是过渡金属，X是一种硫化物，以创建新颖的布尔逻辑器件，其中层之间的扭转角度控制电子特性。提出的项目将开发新的制造技术，表征新的电子特性，然后实现基于这些新开发的异质结构的逻辑器件。该计划将通过促进量子材料和器件跨学科领域的发展，为亚利桑那大学和德克萨斯大学奥斯汀分校创造新的教育和研究机会。特别是，拟议的研究符合美国国家科学基金会的量子飞跃大构想：通过开发有可能实现新量子技术的材料系统和设备来引领下一次量子革命。这一研究计划将着重于对研究生和本科生的培训，从而为他们的工业或学术生涯做好准备。该合作提案将通过异质结构设计、逐层制造、扫描探针显微镜和电输运测量来设计和表征具有平坦带的范德华异质结构器件。该项目将重点研究具有可控层间扭转角的二维半导体过渡金属二硫族化合物的均层异质结构。由于相邻层之间的扭转角，形成了长波长的莫尔条纹，改变了异质结构的电子特性，并导致能量-动量色散是平坦的。这些平坦带具有大的态密度和小的带宽，使得相互作用的影响将超过它们的动能。在这种情况下，电子效应变得高度相关，我们将利用这些特性来创造新的设备。特别是，我们将完成以下三个目标：(1)门可调谐TMD均质层和三层异质结构的开发和表征，(2)通过静电门控，扭转和应变控制创建新的相关状态，以及(3)实现用于布尔逻辑应用的约瑟夫森结场效应晶体管。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Many semiconductor devices rely on creating heterostructures consisting of multiple layers to enable their desired functionality. Traditional semiconductor heterostructures are limited in the choice of materials that can be utilized because of requirements of lattice matching between the different layers. However, atomically thin materials have the ability to overcome this limitation through the creation of van der Waals heterostructures realized in a layer-by-layer stacking approach. This will allow a much wider range of electronic properties to be created in these heterostructures. Furthermore, they have an additional degree of freedom which is the twist angle between different layers, which gives rise to a long wavelength moiré pattern between the layers. This moiré pattern modulates the electronic properties, and can give rise to correlated states such as superconductivity or magnetism. In this project, we will use semiconducting transitional metal dichalcogenides of the form MX2 where M is a transition metal, and X is a chalcogen to create novel Boolean logic devices where the twist angle between layers controls the electronic properties. The proposed project will develop new fabrication techniques, characterize the novel electronic properties, and then implement logic devices based on these newly developed heterostructures. The proposed program will create new educational and research opportunities at University of Arizona and The University of Texas at Austin by fostering the growth of the interdisciplinary area of quantum materials and devices. In particular, the proposed research aligns with the NSF Big Idea of Quantum Leap: Leading the Next Quantum Revolution by developing material systems and devices that have the potential to enable new quantum technologies. This proposed research prog-ram will strongly emphasize the training of graduate and undergraduate students, thus preparing them for industrial or academic careers.This collaborative proposal will engineer and characterize van der Waals heterostructure devices with flat bands through heterostructure design, layer-by-layer fabrication, scanning probe microscopy, and electrical transport measurements. The project will be focused on homobilayer heterostructures of two-dimensional semiconducting transition metal dichalcogenides with controlled twist angle between the layers. Due to the twist angle between adjacent layers, a long wavelength moiré pattern develops which modifies the electronic properties of the heterostructure and can lead to an energy-momentum dispersion that is flat. These flat bands have a large density of states and small bandwidth such that interaction effects will dominate over their kinetic energy. In this regime, the electronic effects become highly correlated and we will exploit these properties for the creation of novel devices. In particular, we will accomplish the following three aims: (1) Development and characterization of gate tunable TMD homobilayer and trilayer heterostructures, (2) Creation of novel correlated states through electrostatic gating, twist and strain control, and (3) Realization of Josephson junction field-effect transistors for Boolean logic applications.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.