CAREER:Visualization and Control of Chiral Bound States and Ballistic Chiral Electrons in Two-Dimensional Material Heterostructures

非技术摘要：这个CAREER项目由一个研究和推广计划组成，解决了关于在纳米级材料中控制非常快（Dirac）电子的基本问题。这些奇异粒子为材料中的电子运动提供了一个令人兴奋的新测试平台，因为它们跨越势垒的行为与正常电子不同。对于狄拉克电子在这些界面上的行为，有许多理论预测，但直到现在还不可能直接测试它们。PI最近开发了一种技术，可以创建具有任意形状的理想纳米级屏障，从而首次实现受限狄拉克电子的成像。狄拉克电子运动的这种控制和可视化将产生深刻的基本见解，为全新的电子设备铺平道路，例如新型传感器和可调纳米级电子透镜。这个职业生涯项目的推广部分将通过使用这个研究项目与现有的NSF研究经验，本科生在加州大学圣克鲁斯（UCSC）增加STEM专业的西班牙裔代表。西班牙裔高中生和来自当地西班牙裔服务机构的高成就社区大学生将在他们的教育发展的三个阶段工作和指导：大学预科，大学早期和大学后期。这些阶段将提供科学的职业意识，以大学预科组，提供机会的研究经验内PI的研究工作的早期大学组，并提供基于职业生涯的辅导和网络的机会，以后期大学组。这些推广工作不仅将使参与的学生受益，也将使UCSC的学生和更广泛的社区受益。技术摘要：这个CAREER项目解决了关于石墨烯和双层石墨烯中手性束缚态和轨迹的基本问题。奇异的准粒子狄拉克费米子，托管在这些二维材料提供了一个新的实验平台，因为它们的手征性质和负能量状态的电子运动。PI最近开发了一种多功能技术来创建具有任意形状的原始纳米级PN结，这使得第一次对受限狄拉克费米子进行成像成为可能。本计画探讨在这些限制势中，势的形状所扮演的角色，以及无质量与有质量狄拉克费米子之间的行为差异。由于狄拉克费米子表现出克莱因隧穿（100%势垒透射）和反克莱因隧穿（100%势垒反射），该项目进行的研究揭示了薛定谔费米子没有发现的新束缚态。此外，引导狄拉克费米子轨迹跨越和响应PN和石墨烯/超导体结映射和比较直接势垒传输和超导的微观模型。狄拉克费米子在这些界面上的行为的理论预测是丰富的，但直到现在还不可能直接测试它们。具体而言，为了揭示手性束缚态和轨迹，该CAREER项目包括三个主要研究工作：（1）可视化和控制由石墨烯和双层石墨烯组成的二维材料异质结构中的手性束缚态。本研究在二维材料异质结构中创建原始的纳米级PN结，并使用扫描隧道显微镜来映射这些PN结内的量子干涉和限制。研究了不同的结形状（圆形与非圆形）和载流子类型（无质量与有质量狄拉克费米子）;（2）可视化和控制二维材料异质结中的弹道手性电子轨迹。本研究使用扫描门显微镜结合纳米级PN结和磁场来映射和引导无质量和有质量狄拉克费米子的弹道轨迹;（3）可视化和控制石墨烯/超导体界面处的手性轨迹。这项研究使用扫描门显微镜在纳米尺度上映射超导体界面的狄拉克费米子反射。该奖项反映了NSF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。

Nontechnical abstract:This CAREER project is composed of a research and outreach plan that addresses fundamental questions regarding the control of very fast (Dirac) electrons in materials at the nanoscale. These exotic particles provide an exciting new testbed for electron motion in materials because their behavior across barriers is distinct from normal electrons. There are many theoretical predictions for the behavior of Dirac electrons at these interfaces, but it has not been possible to directly test them - until now. The PI recently developed techniques to create ideal nanoscale barriers with arbitrary shapes that enable the first imaging of confined Dirac electrons. Such control and visualization of Dirac electron motion will generate deep fundamental insights, paving the way toward entirely new electronic devices, such as novel sensors and tunable nanoscale electronic lenses. The outreach component of this CAREER project will increase Hispanic representation among STEM majors by using this research project with an existing NSF Research Experience for Undergraduates at the University of California Santa Cruz (UCSC). Hispanic high school students and high achieving community college students from Hispanic Serving Institutions from the local area will work and be mentored at three phases in their educational development: pre-college, early-college, and late-college. These stages will provide science career awareness to the pre-college group, provide opportunities for research experiences within the PI's research effort to the early-college group, and provide career-based mentoring and networking opportunities to the late-college group. These outreach efforts will benefit not only the participating students, but also students at UCSC, and the broader community.Technical abstract:This CAREER project addresses fundamental questions regarding chiral bound states and trajectories in graphene and bilayer graphene. The exotic quasiparticles-Dirac fermions, hosted by these two-dimensional materials provide a new testbed for electron motion because of their chiral nature and negative energy states. The PI recently developed a versatile technique to create pristine nanoscale PN junctions with arbitrary shapes, which enabled the first imaging of confined Dirac fermions. This project investigates the role of the potential shape and the differences in behavior between massless and massive Dirac fermions within these confinement potentials. Because Dirac fermions exhibit Klein tunneling (100% barrier transmission) and anti-Klein tunneling (100% barrier reflection), the research carried out by this project reveals novel bound states not found with Schrödinger fermions. Moreover, steered Dirac fermion trajectories across and in response to PN and graphene/superconductor junctions are mapped and compared directly to microscopic models for barrier transmission and superconductivity. Theoretical predictions for the behavior of Dirac fermions at these interfaces are abundant, but it has not been possible to directly test them - until now. Specifically, to reveal chiral bound states and trajectories this CAREER project contains three main research efforts: (1) Visualize and control chiral bound states in two-dimensional material heterostructures composed of graphene and bilayer graphene. This study creates pristine nanoscale PN junctions in two-dimensional material heterostructures and use scanning tunneling microscopy to map quantum interference and confinement within these PN junctions. Different junction shapes (circular vs. non-circular) and charge carrier types (massless vs. massive Dirac fermions) are investigated; (2) Visualize and control ballistic chiral electron trajectories in two-dimensional material heterostructures. This study uses scanning gate microscopy in conjunction with nanoscale PN junctions and magnetic fields to map and steer ballistic trajectories of massless and massive Dirac fermions; (3) visualize and control chiral trajectories at a graphene/superconductor interface. This study uses scanning gate microscopy to map Dirac fermion reflections off a superconductor's interface at the nanoscale.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.