Coherence and Fluctuations in Novel Multicomponent Systems

技术概述：该奖项支持低维、多组分凝聚态系统的理论研究和教育，这些凝聚态系统具有离散的自由度，如自旋、山谷或层。基本物理通常可以用有效自由度来理解，而不是基础电子的有效自由度，从而允许简化描述不能用标准费米液体理论来理解的起伏或关联态。PI将专注于两个特定的系统作为范例：石墨烯和量子霍尔双层膜。石墨烯是一个二维碳网络，由于几个原因，它在二维电子气系统中是不寻常的。费米能级附近的电子是“无质量的”，遵循狄拉克方程。这导致了与相对论粒子的“克莱因悖论”有关的独特物理学，在该悖论中，电子流可以通过空穴状态的混合物穿透势垒。在石墨烯中，这意味着电子不能仅受静电势的限制。这将对破坏空间对称性的多体状态以及基于它们的涨落感生状态的后果进行检验。PI还将研究山谷自由度的影响，这种自由度允许在这种状态下出现异常有序的可能性，特别是在量子霍尔体系中。此外，次晶格自由度导致了不寻常的Berry相，并对输运和干扰效应产生了许多有趣的后果，这也将被研究。PI将调查曲率和拓扑缺陷对石墨烯电子性质的影响。填充因子1附近的量子霍尔双层膜的特殊之处在于表现出一种不完美的超流性--在零温度极限下似乎消失的逆流阻力，以及隧道电导中的强烈但有限的共振。允许这种不寻常行为出现的潜在状态仍然知之甚少。PI的目的是在无序发挥关键作用的前提下，确定量子涨落可能如何导致这种行为。旨在理解这一背景下的一些最新实验的研究也将继续进行。非技术总结：该奖项支持在两个空间维度上关于材料电子态的基础理论研究和教育。这位PI将专注于石墨烯和量子霍尔双层-强磁场中电子的两层系统-的研究。这些系统中的每一个都有与标准教科书智慧截然不同的电子状态。例如，石墨烯中的电子行为就像光的粒子，并受爱因斯坦在量子世界中重塑的相对论的支配。量子霍尔双层显示了一种新的物质状态，看起来像是不完美的超导体。这项工作代表了寻求理解这些新的物质状态的基础研究。石墨烯也是新技术的重要候选者。这项研究有助于理解石墨烯的不同寻常的性质，并为使新技术保持美国竞争力的知识库做出贡献。这项研究将在研究生的全面参与下进行，他们将接受分析凝聚态系统的现代方法的培训，为他们在科学和技术领域的职业生涯做好准备。最后，这项研究将与来自美国和国外的科学家合作进行，加强和丰富美国物理界。

TECHNICAL SUMMARY:This award supports theoretical research and education on low-dimensional, multicomponent condensed matter systems which have discrete degrees of freedom, such as spin, valley, or layer. The essential physics may often be understood in terms of effective degrees of freedom other than those of the underlying electrons, allowing for simplified descriptions of fluctuating or correlated states that cannot be understood in terms of standard Fermi liquid theory. The PI will focus on two specific systems as paradigms: graphene and quantum Hall bilayers.Graphene, a two-dimensional carbon network, is unusual among two-dimensional electron gas systems for several reasons. The electrons near the Fermi level are "massless," and obey a Dirac equation. This leads to unique physics related to the "Klein paradox" for relativistic particles, in which an electron current may penetrate a barrier via the admixture of hole states. In graphene this implies that electrons cannot be confined solely by an electrostatic potential. The consequences of this for many-body states of broken spatial symmetries, and fluctuation-induced states based upon them, will be examined. The PI will also study the impact of the valley degree of freedom which allows the possibility of unusual orderings in such states, particularly in the quantum Hall regime.In addition, the sublattice degree of freedom leads to an unusual Berry's phase with many interesting consequences for transport and interference effects, which will also be examined. The PI will investigate consequences of curvature and topological defects for the electronic properties of graphene. Quantum Hall bilayers near filling factor 1 are special in displaying an "imperfect" superfluidity - a counterflow resistance that appears to vanish in the zero temperature limit, and a strong but finite resonance in tunneling conductance. The underlying state that allows such unusual behavior to emerge remains poorly understood. The PI aims to determine how quantum fluctuations may lead to such behavior, under the premise that disorder plays a crucial role. Studies designed to understand some recent experiments within this context will also be pursued.NON-TECHNICAL SUMMARY:This award supports fundamental theoretical research and education on the electronic states of materials in two spatial dimensions. The PI will focus his research on graphene and quantum Hall bilayers - two layer systems of electrons in high magnetic fields. Each of these systems has electronic states that differ dramatically from standard textbook wisdom. For example, the electrons in graphene behave like particles of light and are governed by Einstein's theory of relativity recast in the quantum world. The quantum Hall bilayers exhibit a new state of matter that appears like an imperfect superconductor. This work represents fundamental research that seeks to understand these new states of matter. Graphene is also an important candidate for new technologies. This research contributes to understanding graphene's unusual properties and contributes to the knowledge base that will enable new technologies to keep America competitive. This research will be conducted with the full participation of graduate students, who will be trained in modern methods for analyzing condensed matter systems, preparing them for careers in science and technology. Finally the research will be performed in collaboration with scientists from the US and abroad, strengthening and enriching the US physical community.