NIRT: Coherence and Correlation in Electronic Nanostructures

Duke University, Durham NC

Investigators

Abstract

0103003 Baranger This proposal was submitted in response to the solicitation "Nanoscale Science and Engineering" (NSF-00-119). The resulting grant is co-funded by the Divisions of Materials Research, Chemistry and Physics. The proposed research will investigate quantum interference (coherence) and electron-electron interactions (correlations) in both model and realistic systems over a wide range of spatial scales, from nanometers to microns. The interplay of correlations and coherence is one of the deepest topics in current chemistry and physics. Nanostructures provide a novel controlled environment for studying these effects: both interactions and interference can be manipulated by changing the size and shape of the nanostructure, thereby directly gaining information on their interplay. The principal investigators (PI's) will calculate the results of such manipulation in several prototypical cases spanning size scales from one nanometer to one micron. Furthermore, a number of long-range technologies being investigated involve electron-electron interactions and quantum interference in their operation - single electronics, spintronics, molecular electroncs, and quantum computing, for instance. The PI's plan to investigate coherence and correlation in these possible device structures. Thus, the project will contribute to the knowledge base needed to evaluate the practical relevance of these nascent nanotechnologies. More precisely, four scale sizes will be studied: correlations at the scale of the electron wavelength, simple single and multiple quantum dots, metallic "nanomolecules," and finally, networks of carbon nanotubes. Three computational techniques will be used - quantum Monte Carlo (QMC), full density functional theory (DFT), and a simplified density functional technique suitable for nanotubes. These electronic structure techniques will be combined with the semianalytic techniques of random matrix theory and semiclassical theory developed recently in nanophysics. Each of the computational techniques requires substantial innovation. In the case of QMC, the "fermion sign problem" will be atacked by using the recently developed cluster-type algorithms. For the metallic nanomolecules, teh full DFT code must be modified to properly include spin-orbit effects critical in spintronics. And for the simplified DFT method, the recently developed linear-scaling and self-consistent tight-binding methods must be combined and optimized for carbon nanotubes. The computations will be done on a parallel beowulf-class cluster of processors. The specific issues which the PI's intend to elucidate include: (1) the combination of Coulomb blockade and single-particle quantization effects in quantum dots and nanoparticles and their relevance for single-electronic devices; (2) correlation effects at the "soft edge" of quantum dots; (3) the role of disorder and pairing correlations in transport through nanoparticles; (4) the spin states, magnetic moment, and anisotropy energy of metallic nanomolecules and, deduced from these, their spintronic properties; (5) the robustness of entangled states in multiple quantum dots of interest for quantum computing; and, (6) the interactive behavior of a large collection of carbon nanotube quantum dots - an "artificial macromolecule." %%% This proposal was submitted in response to the solicitation "Nanoscale Science and Engineering" (NSF-00-119). The resulting grant is co-funded by the Divisions of Materials Research, Chemistry and Physics. The proposed research will investigate quantum interference (coherence) and electron-electron interactions (correlations) in both model and realistic systems over a wide range of spatial scales, from nanometers to microns. The interplay of correlations and coherence is one of the deepest topics in current chemistry and physics. Nanostructures provide a novel controlled environment for studying these effects: both interactions and interference can be manipulated by changing the size and shape of the nanostructure, thereby directly gaining information on their interplay. The principal investigators (PI's) will calculate the results of such manipulation in several prototypical cases spanning size scales from one nanometer to one micron. Furthermore, a number of long-range technologies being investigated involve electron-electron interactions and quantum interference in their operation - single electronics, spintronics, molecular electroncs, and quantum computing, for instance. The PI's plan to investigate coherence and correlation in these possible device structures. Thus, the project will contribute to the knowledge base needed to evaluate the practical relevance of these nascent nanotechnologies. ***