NIRT: Coherence and Correlations in Electronic Nanostructures

Duke University, Durham NC

Investigators

Abstract

TECHNICAL EXPLANATION: This award is made on a NIRT category proposal received in response to the Nanoscale Science and Engineering solicitation, NSF 04-043. The Division of Materials Research, the Chemistry Division, the Division of Mathematical Sciences, and the Physics Division contribute support for this theoretical and computational research and education. This project is focused on the interplay between coherence and correlation, which is a central issue in quantum nanoscience. Coherence gives rise to interference effects, while correlation is the organization of electrons with respect to each other that arises as a consequence of their mutual repulsion. The interplay between the two occurs particularly at the nanoscale: Quantum interference is strong because the system is smaller than the dephasing length; the resulting density modulation gives rise to strong electron-electron (e-e) interaction effects. These effects can be tuned, providing in solid-state quantum systems an unprecedented level of control. The PIs will study quantum coherence and electron-electron interactions in both model and realistic systems from nm to mm with an aim to elucidate the interplay between these two effects in nanostructures. The work will contribute to the knowledge base needed to evaluate the practical relevance of these nascent nanotechnologies and to fundamental research on one of the deepest topics in current chemistry and physics. The PIs will concentrate on three specific thrusts: 1. Conductance of single molecules: The PIs plan computational investigations of candidate molecules searching for evidence of switching, rectification, and the presence of negative differential resistance. Theoretical and computational methods will be further developed, including an optimized effective potential approach and a method for which computational effort scales linearly with the number of atoms. The PIs plan to tackle the fundamental issue of interaction effects in electron transport through molecules. 2. Low density dots and wires: Correlation effects are enhanced by low electron density. Using quantum Monte Carlo methods, the PIs will calculate properties of both circular and irregular quantum dots, paying particular attention to signatures of local order. In quantum wires, they plan to investigate the Matveev scenario for the "0.7 plateau." 3. Quantum dots as quantum impurities: The interaction of a quantum dot with a lead, as in, for example, a qubit with a readout electrode, can be mapped onto quantum impurity problems. The PIs will begin by characterizing the role of mesoscopic fluctuations in quantum dot-lead systems. The PIs will study realizations of multichannel impurity problems, as well as systems of multiple quantum dots. Undergraduate, graduate, and postdoctoral researchers will be involved in all aspects of this project. Beyond the core team at Duke, the project involves three other senior researchers, one each at Cornell, at Argonne National Lab, and in France. It builds inter-university, university-national lab, and international collaborations. This project incorporates two outreach components: (1) Participation in Duke's nationally recognized programs for involving undergraduates from underrepresented groups in summer research. (2) Participation in a program of summer lectures for high school teachers on frontier topics in chemistry. NON-TECHNICAL EXPLANATION: This award is made on a NIRT category proposal received in response to the Nanoscale Science and Engineering solicitation, NSF 04-043. The Division of Materials Research, the Chemistry Division, the Division of Mathematical Sciences, and the Physics Division contribute support for this award. This theoretical and computational research project is focused on fundamental phenomena displayed by electrons particularly in nanoscale structures of atoms such as quantum dots and quantum wires. Central to this study is the interplay between the wave nature of electrons and the interactions between them. Nanoscale structures of atoms and large molecules may provide a controlled environment to study this interplay. The effects that arise and their manipulation are of fundamental scientific interest in elucidating the nature of the quantum mechanical world and may also help provide the operating principles for future nanoscale electronic devices. Undergraduate, graduate, and postdoctoral researchers will be involved in all aspects of this project contributing to the training of the next generation theoretical and computational scientists. Beyond the core team at Duke, the project involves three other senior researchers, one each at Cornell, at Argonne National Lab, and in France. It builds inter-university, university-national lab, and international collaborations. This project incorporates two outreach components: (1) Participation in Duke's nationally recognized programs for involving undergraduates from underrepresented groups in summer research. (2) Participation in a program of summer lectures for high school teachers on frontier topics in chemistry.