NSF-BSF: Quantum Electron States in van der Waals Platforms

美国国家科学基金会和美国-以色列双国科学基金会(BSF)共同支持一名美国研究人员和一名以色列研究人员之间的合作。美国国家科学基金会材料研究部(DMR)资助了这一奖项，该奖项支持专注于了解由少量二维层堆叠而成的材料物理的研究和教育活动。当电子系统被限制在低维时，它们的量子物理变得非常丰富，导致系统具有奇异的性质。在这个项目中，研究小组将研究由单个或少量薄片组成的系统，这些薄片层叠在一起形成复合的二维电子平台。可用于建造这些系统的材料已经变得越来越多样化，提供了各种各样的可能性。各个层可以是相同的材料，一个突出的例子是由两个相互扭曲的石墨烯薄片制成的双层。最近已经证明，这支持显著的绝缘态和超导态，只有电子密度的微小差异决定了这些行为的表现。在其他情况下，系统可能由完全不同的材料层组成，彼此之间只有很弱的粘连，因此它们的基本个体结构保持完好。将这些结构结合在一起，可以得到与其组成成分完全不同的电子性质的体系。在这个项目中，该团队将探索这些材料系统中奇异的量子电子态，以及它们所展示的可测量的性质，这可能会找到技术应用。作为NSF和BSF的合作，这个项目将为年轻的物理学家提供宝贵的培训，学习分析电子材料的方法，以及学习在国际环境下工作和合作。年轻的女性理科学生将受益于以色列高级参与者定期访问印第安纳大学，她将与物理系女性科学小组的学生以及印第安纳大学STEM生活和学习中心的本科生进行接触，在那里她将成为访问教员。国际学生联合会将参加一年一度的国际科学节的外展活动，届时将为在校儿童介绍以物理为基础的互动活动。PI还将指导密歇根大学物理系桥接项目的学生。通过这些活动，两个参与者都将寻求让来自代表性不足群体的学生参与到这个项目中来。美国国家科学基金会和美国-以色列双国科学基金会(BSF)共同支持一名美国研究人员和一名以色列研究人员之间的合作。美国国家科学基金会材料研究部(DMR)资助了这一奖项，该奖项支持范德华平台中量子电子态的研究和教育活动。要研究的特定系统涉及石墨烯、过渡金属二卤化物(TMD)层、黑磷层(BP)和拓扑绝缘体表面的组合。例如，石墨烯-TMD异质结构为电子和空穴提供了一个非常不均匀的平台，前者支持无隙狄拉克电子态，后者支持空穴状态下不寻常的自旋-轨道耦合。在这些系统中，研究小组将考虑层间粒子-空穴对--激子--形成凝聚态的可能性，这种凝聚体的行为在两种物质中都是出乎意料的(例如，山谷超流体)。BP的高度各向异性结构提供了在石墨烯等合作材料中诱导强烈各向异性的可能性，该团队将探索这对石墨烯电子的单粒子和集体行为的影响，包括诱导超导或电荷密度波态的可能性。对在TI表面上排列的石墨烯的研究，其中微结构形成具有大的单位单元的莫尔图案，将集中在具有自发破坏的对称性的量子霍尔态上，其中TI的相反表面拥有非常不同的电子态，在拓扑上连接在一起。该项目还包括对扭曲的双层石墨烯的研究，重点是在Mott绝缘/超导状态附近观察到的磁场效应，在那里可能会出现新的电子有序。作为NSF和BSF的合作，该项目将为年轻物理学家提供宝贵的培训，学习分析电子材料的方法，以及学习在国际环境下工作和合作。年轻的女性理科学生将受益于以色列高级参与者定期访问印第安纳大学，她将与物理系女性科学小组的学生以及印第安纳大学STEM生活和学习中心的本科生进行接触，在那里她将成为访问教员。国际学生联合会将参加一年一度的国际科学节的外展活动，届时将为在校儿童介绍以物理为基础的互动活动。PI还将指导密歇根大学物理系桥接项目的学生。通过这些活动，两位参与者将寻求让代表不足的群体的学生参与到这个项目中来。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

NONTECHNICAL SUMMARYThe National Science Foundation and the United States-Israel Binational Science Foundation (BSF) jointly support this collaboration between a US-based researcher and an Israel-based researcher. The NSF Division of Materials Research (DMR) funds this award, which supports research and educational activities focused on understanding the physics of materials composed by stacking together a small number of two-dimensional layers.The quantum physics of electronic systems becomes very rich when they are confined to low dimensions, resulting in systems with exotic properties. In this project, the research team will investigate systems composed of single or small number of sheets, layered together into composite two-dimensional electron platforms. The materials available for building these systems have become increasingly diverse, offering a great variety of possibilities. Individual layers may be of the same material, with a prominent example being a bilayer made from two graphene sheets twisted relative to each other. This has recently been demonstrated to support remarkable insulating and superconducting states, with only a small difference in electron density determining which of these behaviors manifests. In other cases, the system may comprise layers of completely different materials, adhering to one another only weakly, so that their basic individual structures remain intact. Combining such structures can result in systems with electronic properties completely different than those of their constituents. In this project the team will explore exotic quantum electron states in these material systems, and the measurable properties they exhibit, which could find technological applications.As an NSF-BSF collaboration, this project will provide valuable training for young physicists, in methods for analyzing electronic materials, as well as in learning to work and collaborate within an international setting. Young women science students will benefit from regular visits to Indiana University by the senior Israeli participant, who will engage with students in the Women in Science group in the Physics Department, as well as with undergraduates at IU's STEM Living and Learning Center where she will become a visiting faculty fellow. The PI will participate in outreach at the annual IU ScienceFest, for which physics-based interactive activities for school children will be introduced. The PI will also mentor students in the IU Physics Department's Bridge Program. Through these activities both participants will seek to involve students from under-represented groups in this project.TECHNICAL SUMMARYThe National Science Foundation and the United States-Israel Binational Science Foundation (BSF) jointly support this collaboration between a US-based researcher and an Israel-based researcher. The NSF Division of Materials Research (DMR) funds this award, which supports research and educational activities focused on quantum electron states in van der Waals platforms.The specific systems to be studied involve combinations of graphene, transition metal dichalcogenide (TMD) layers, layers of black phosphorus (BP), and surfaces of topological insulators. A graphene-TMD heterostructure, for example, provides a very heterogeneous platform for electrons and holes, with the former supporting gapless Dirac electron states and the latter supporting unusual spin-orbit coupling in its hole states. In these systems, the team will consider the possibility of interlayer particle-hole pairs --excitons-- forming a condensate with behavior unexpected in either material individually (e.g., a valley superfluid.) The highly anisotropic structure of BP offers the possibility of inducing strong anisotropy in a partnered material such as graphene, and the team will explore the effects of this on both the single-particle and collective behavior of the graphene electrons, including the possibility of inducing superconductivity or charge-density-wave states. Studies of aligned graphene on a TI surface, in which the microstructure forms a moire pattern with a large unit cell, will focus on quantum Hall states with spontaneously broken symmetry, where opposing surfaces of the TI, hosting very different electronic states, are topologically tied together. The project also involves studies of twisted bilayer graphene, focusing on observed magnetic field effects in the vicinity of the Mott insulating/superconducting states, where novel electronic ordering may be occurring.As an NSF-BSF collaboration, this project will provide valuable training for young physicists, in methods for analyzing electronic materials, as well as in learning to work and collaborate within an international setting. Young women science students will benefit from regular visits to Indiana University by the senior Israeli participant, who will engage with students in the Women in Science group in the Physics Department, as well as with undergraduates at IU's STEM Living and Learning Center where she will become a visiting faculty fellow. The PI will participate in outreach at the annual IU ScienceFest, for which physics-based interactive activities for school children will be introduced. The PI will also mentor students in the IU Physics Department's Bridge Program. Through these activities both participants will seek to involve students from under-represented groups in this project.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.