Coulomb drag in ultra-clean and strongly interacting van der Waals materials: toward exciton condensation

超洁净和强相互作用范德华材料中的库仑阻力：朝向激子凝聚

• 批准号: 1507788
• 负责人: Cory Dean
• 金额: $ 40.5万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-06-01 至 2018-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1507788&HistoricalAwards=false
• 关键词: Coulomb; drag; ultra; clean; strongly

Non-technical AbstractThe aim of this project is to experimentally study the interactions between electrons in two coupled two-dimensional (2D) sheets. When the 2D layers are sufficiently close, interlayer Coulomb interactions result in momentum transfer so that electrons moving in one layer cause those in the second sheet to move in response, a phenomenon known as Coulomb drag. This work will study layered heterostructures of atomically thin materials -- including graphene and insulating boron nitride --to achieve atomic control over the spacing between the conducting layers. This will allow the exploration of Coulomb drag in the strong-coupling limit, and in high-mobility devices where electrical transport is ballistic. These structures are made possible by techniques developed by the Principle Investigators to fabricate ultraclean multi-layered heterostructures by mechanical layering of 2D materials. The primary effort will be a systematic characterization of the drag response in monolayer graphene versus temperature, density, layer separation, and magnetic field. Drag resistance together with inter-layer tunneling will additionally be used to pursue signatures of a theoretically-predicted exciton condensate phase in which spatially indirect excitons consisting of paired electrons and holes confined to separate layers condensed into a superfluid ground state. Careful studies of the Coulomb drag response provides a unique tool in which to study electron-electron interactions in mesoscopic systems, which is expected to have significant impact beyond the study of 2D systems, since electron-electron interactions underlie the rich and complex physics of correlated materials. If successful, this research could also enable revolutionary new low power electronic devices. The collaborative interdisciplinary work will provide training to a postdoctoral researcher as well as providing research experience to high school and junior level undergraduate students. Outreach efforts will focus on expanding long-term relationships with teachers at two affiliated public schools. Technical Abstract: The aim of this project is to experimentally study Coulomb drag in high mobility double layer quantum wells fabricated from 2D materials, such as graphene and related van der Waals materials, in the strongly interacting limit of small interlayer separation. The primary goal will be a systematic characterization of the drag response in monolayer graphene heterostructures versus temperature, density and interlayer separation, under both zero and finite magnetic field, through transport measurements. Several outstanding questions will be addressed such as the anomalous density and temperature dependences reported previously, origin of the anomalous drag response at the double neutrality point, and the nature of the Hall response in the finite magnetic field regime. Drag resistance together with inter-layer tunneling will additionally be used to pursue signatures of the exciton condensate phase in two regimes (i) electron-hole graphene layers at zero magnetic field, and (ii) electron-electron graphene layers at half filled Landau levels in the quantum Hall regime. The experimental effort will include studies of heterostructures fabricated from bilayer graphene, and mono and few-layer transition metal dichalcogenides where the effect of a bandgap on the exciton binding has so far received no experimental attention. The Coulomb drag response in graphene is not well understood at the most basic level. Theoretical efforts to model this system have yielded conflicting results, none of which well match the few experimental studies that have been reported so far. In this regard the systematic study proposed here promises to lay important groundwork for future understanding of this system, and more generally to provide quantitative boundaries on key physical parameters necessary to accurately model electron transport in graphene such as the strength of electron screening versus density and the specific role of the dielectric environment.

非技术摘要该项目的目的是实验研究两个耦合的二维（2D）表中的电子之间的相互作用。 当2D层足够接近时，层间库仑相互作用会导致动量转移，从而使一个层移动的电子会导致第二张纸中的那些人移动，这是一种称为库仑阻力的现象。这项工作将研究原子薄材料的分层异质结构（包括石墨烯和氮化硼），以实现对导电层之间间距的原子控制。 这将允许在强耦合极限以及电气传输是弹道的高驾驶设备中探索库仑阻力。 这些结构是由主要研究人员开发的技术使这些结构成为可能的，该技术通过2D材料的机械分层来制造超细胞多层异质结构。 主要的工作将是单层石墨烯与温度，密度，层分离和磁场中阻力响应的系统表征。阻力阻力以及层间隧道还将用于追求理论上预测的激子冷凝水相的特征，在该阶段中，该相位在空间间接间接激子中由配对电子和孔组成的空间间接激子，限制在分离到超级流体基态状态的分离层。仔细研究库仑阻力响应提供了一种独特的工具，可以在其中研究中镜系统中的电子电子相互作用，因为电子 - 电子相互作用是相关材料的丰富且复杂的物理学，因此预计将在2D系统的研究之外产生重大影响。 如果成功，这项研究还可以实现革命性的新低功率电子设备。 合作的跨学科工作将为博士后研究人员提供培训，并为高中和初中的本科生提供研究经验。 外展工作将着重于扩大两所关联公立学校的教师的长期关系。技术摘要：该项目的目的是实验研究由2D材料（例如石墨烯和相关的范德华材料）制成的高迁移率双层量子井中的库仑阻力，在小型层间分离的强度相互作用的极限下。 主要目标是通过传输测量值在零和有限磁场下的单层石墨烯异质结构中的阻力响应与温度，密度和层间分离的系统表征。将解决几个未出现的问题，例如先前报告的异常密度和温度依赖性，双中性点在双中性点处的异常阻力响应的起源以及在有限磁场状态下HALL响应的性质。 阻力阻力以及层间隧道还将用于在零磁场的两个机制（i）电子孔石墨烯层中追求激子冷凝物相的特征，（ii）在量子霍尔制度中的一半填充兰道水平的电子电子石墨烯层。实验性工作将包括研究由双层石墨烯制成的异质结构，以及单层和几层过渡金属二核苷，其中带隙对激子结合的影响迄今尚未受到实验性关注。石墨烯中的库仑阻力响应在最基本的水平上尚未得到很好的了解。对该系统进行建模的理论努力已经产生了矛盾的结果，而这些结果却没有很好地与迄今为止报道的少数实验研究相匹配。在这方面，此处提出的系统研究有望为将来对该系统的理解奠定重要的基础，并且更普遍地为准确地模拟石墨烯中电子传输所需的关键物理参数提供定量界限，例如电子筛选的强度与密度和介电环境的特定作用。