Theory of Graphene and the Spin Hall Effect

University Of Pennsylvania, Philadelphia PA

Investigators

Abstract

TECHNICAL SUMMARY: This award supports theoretical research and education on the novel properties of graphene, a novel two-dimensional form of carbon. Experiments on this material reveal novel and unexpected properties. The PI will study these properties that are of fundamental interest in condensed matter physics and may affect applications to nanoelectronics and spintronics. The principal investigator will work closely with his students on this project. Theoretical research will focus on two broad topics: (i) the electronic properties of graphene, and (ii) the spin Hall effect in semiconductors and insulators. The proposed work will explore the interplay between topological aspects of band theory, disorder and interactions. The first topic is motivated by recent experiments which demonstrate that the detailed experimental study of individual planes of graphene is now feasible. These experiments point to a number of fundamental problems for theory for the ideal semimetallic electronic structure of graphene. The goal of this part of the project is to elucidate the experimental consequences of graphene's unique electronic bandstructure and to understand the effects of disorder and electron electron interactions. Specific problems to be addressed include: (1) the interplay between disorder and interactions for Dirac fermions in graphene, (2) the physics of the quantum Hall effect in graphene, and (3) physical phenomena for likely experimental geometries, such as pn junctions and bilayer structures, quantum dots and edges. The experimental study of graphene is presently in its very early stages. We expect that the work proposed here will impact the subsequent development of the field and will contribute to the knowledge base necessary to develop potential electronic applications. The second topic concerns the theory of the quantum spin Hall effect, which the PI has recently proposed to occur in graphene. In addition to its direct connection to graphene, this work will address issues in the broader field of the spin Hall effect in metals and semiconductors. If it can be observed, the quantum spin Hall effect offers the enticing possibility of dissipationless flow of spin in a material that is otherwise an insulator. The goals of this part of the project are: (1) to provide a solid theoretical foundation for the quantum spin Hall effect, (2) to establish the appropriate signatures for its experimental observation, and (3) discover other materials, besides graphene which may exhibit this effect. The broader impact of the proposed work involves both the potential for technological innovation and the development of human resources. Graphene has potential to provide a basis for novel carbon based electronic devices. Moreover, the spin Hall effect may have useful long-term applications in the emerging field of spintronics. The problems that arise in the course of the research will be ideal for training a graduate student in the modern methods of condensed matter theory. The PI also plans to develop a series of lectures for sophomore undergraduates with the goal of introducing the students to the physics of electronic materials as well as to the nature of theoretical physics. NON-TECHNICAL SUMMARY: This award supports theoretical research and education on the novel properties of graphene, a novel two-dimensional form of carbon. Experiments on this material reveal novel and unexpected properties. The PI will study these properties that are of fundamental interest in condensed matter physics and may affect applications to nanoelectronics and spintronics. The principal investigator will work closely with his students on this project. Research will focus on the quantum mechanical states of electrons in graphine and effect of imperfections and impurities on these states. The PI will also study exotic states of electronic matter and phenomena that arise with the application of a strong magnetic field. As a consequence of its quantum mechanical nature, an electron has spin, an intrinsic amount of angular momentum, as if it were like a tiny spinning top. The discovery and fundamental understanding of phenomena associated with electron spins and their motion in graphine constitutes a focus of the PI's research. This research contributes to the intellectual foundations of the emerging field of spintronics in which spins as well as charges are used in device technologies. The problems that arise in the course of the research will be ideal for training a graduate student in the modern methods of condensed matter theory. The PI also plans to develop a series of lectures for sophomore undergraduates with the goal of introducing the students to the physics of electronic materials as well as to the nature of theoretical physics.