CAREER: Correlated Topological States in van der Waals Bilayers

二维材料是由只有一到两个原子厚的原子层组成，排列成完美的晶格。这些材料制造的最新进展导致了新型电子设备的发展，这可以帮助推动缩放电子元件的边界或引入基于全新功能的电子设备。至关重要的是，在极薄的层中，系统的量子特性以一种新的、不寻常的方式主导着电子特性。例如，自发有序，类似于铁磁性，可以发生在层之间。电场可用于改变材料特性，为增强量子电子器件的功能提供了新的可能性。该项目开发了一种新的超灵敏电容技术来研究这些材料，以及基于二维材料的电子设备的新架构。测量工具包将帮助其他科学家在该领域研究与电子和能量收集相关的设备，同时在创造更完美的二维设备方面的持续进步揭示了低维电子物质的新物理学。本科生和研究生在实验设计，设备制造和低温测量方面进行培训，推动新一代凝聚态物理学家准备好应对材料和测量科学中的挑战性问题。技术摘要：本CAREER项目开发了一种电容测量技术，可以直接感知原子双层中的电子压缩性、层极化和层极化率，特别是在新一代全范德华器件几何结构中，其中栅极介电材料和金属材料（除了通道材料）也是由完美的二维晶体制成的。测量技术依赖于电子层间运动引起的双层和两个近端栅极之间的几何电容的微小差异，使用多路高电流增益低温放大器检测。该活动详尽地分类了石墨烯异质结构中的整数和分数量子霍尔效应以及对称保护边缘状态，使用了分别探测体和边缘的热力学和电荷输运技术的组合。直接目标包括超干净的伯纳和扭曲双层石墨烯，其中该技术允许消除自旋，层和谷对称性破缺的歧义。器件采用全范德华封装新技术制造，可实现创纪录的高移动性，可与所有其他电子系统相媲美或超越。此外，对半导体双层中电荷转移的精确测量可以对光诱导过程进行定量基准测试，这与能量收集有关。除了提供二维材料应用中使用的材料参数的直接定量基准外，该活动通过本科和研究生研究人员教育的无缝集成以及基于数字和模拟电子学的高中水平课堂模块的开发，具有更广泛的影响。

Non-Technical AbstractTwo dimensional materials are composed of layers of atoms only one or two atoms thick, arranged in a perfect lattice. Recent advances in the fabrication of these materials have led to the development of new types of electronic devices, which can help push the boundaries of scaling electronic components or introduce electronic devices based on completely new functionality. Crucially, in extremely thin layers the quantum nature of the system dominates the electronic properties in new and unusual ways. For example, spontaneous ordering, similar to ferromagnetism, can occur between layers. Electric fields can be used to modify material properties, providing new possibilities for enhancing the functionality of quantum electronic devices. This project develops a new, ultrasensitive capacitive technique to study these materials, along with new architectures for electronic devices based on two dimensional materials. The measurement toolkit will aid other scientists in the field studying devices relevant to electronics and energy harvesting, while continued advances in creating ever more perfect two dimensional devices reveal new physics of low dimensional electronic matter. Undergraduate and graduate students are trained in experimental design, device fabrication, and cryogenic measurement, advancing a new generation of condensed matter physicists ready to take on challenging problems across materials and measurement science.Technical abstractThis CAREER project develops a capacitive measurement technique that directly senses electronic compressibility, layer polarization, and layer polarizability in atomic bilayers, particularly within a new generation of all-van der Waals device geometries in which gate dielectric and metal materials (in addition to the channel materials) are also made of perfect two dimensional crystals. The measurement technique relies on the small difference in geometric capacitance between a bilayer and two proximal gates caused by interlayer motion of electrons, detected using a multiplexed high current gain cryogenic amplifier. The activity exhaustively catalogues integer and fractional quantum Hall effects and symmetry protected edge states in graphene heterostructures using a combination of thermodynamic and charge transport techniques which probe the bulk and edge separately. Immediate targets include ultra-clean Bernal and twisted bilayer graphene, where the technique permits the disambiguation of spin, layer, and valley symmetry breaking. Devices are fabricated using a new technique of all-van der Waals encapsulation, allowing record high mobilities rivalling or surpassing what can be achieved in all other electronic systems. Precise measurements of charge transfer in semiconductor bilayers, moreover, allows quantitative benchmarking of photo-induced processes, as are relevant for energy harvesting. In addition to providing direct, quantitative benchmarking of material parameters of use in applications of two dimensional materials, the activity has a broader impact through the seamless integration of undergraduate and graduate researcher education, and the developments of high school level classroom modules based on digital and analog electronics.