NIRT: Coherence and Correlation in Electronic Nanostructures

0103003Baranger本提案是应《纳米科学与工程》(NSF-00-119)征集而提交的。由此产生的拨款由材料研究、化学和物理部门共同资助。这项拟议的研究将在从纳米到微米的广泛空间尺度上研究模型和现实系统中的量子干涉(相干)和电子-电子相互作用(关联)。关联和相干的相互作用是当前化学和物理中最深入的主题之一。纳米结构为研究这些效应提供了一种新的受控环境：相互作用和干扰都可以通过改变纳米结构的大小和形状来操纵，从而直接获得关于它们相互作用的信息。首席研究员(PI)将计算从一纳米到一微米的几个典型案例中这种操纵的结果。此外，正在研究的一些远程技术在其操作中涉及电子-电子相互作用和量子干扰-例如，单电子学、自旋电子学、分子电子学和量子计算。PI计划调查这些可能的器件结构中的连贯性和相关性。因此，该项目将有助于评估这些新兴纳米技术的实用相关性所需的知识库。更准确地说，将研究四个尺度：电子波长尺度的相关性，简单的单个和多个量子点，金属“纳米分子”，最后是碳纳米管网络。将使用三种计算技术-量子蒙特卡罗(QMC)、全密度泛函理论(DFT)和适用于纳米管的简化密度泛函技术。这些电子结构技术将与纳米物理学中最近发展起来的随机矩阵理论和半经典理论的半解析技术相结合。每一种计算技术都需要实质性的创新。在QMC的情况下，“费米子符号问题”将使用最近发展的簇型算法来解决。对于金属纳米分子，必须修改完整的DFT代码，以适当地包括在自旋电子学中至关重要的自旋轨道效应。而对于简化的密度泛函方法，最近发展的线性标度方法和自洽紧束缚方法必须结合和优化适用于碳纳米管。计算将在一个平行的Beowulf类处理器集群上进行。PI打算阐明的具体问题包括：(1)量子点和纳米粒子中库仑阻塞和单粒子量子化效应的组合及其与单电子器件的相关性；(2)量子点“软边缘”的关联效应；(3)无序和配对关联在纳米粒子传输中的作用；(4)金属纳米分子的自旋态、磁矩和各向异性能量以及由此推导出的它们的自旋电子学性质；(5)量子计算中感兴趣的多个量子点中纠缠态的稳健性；以及(6)大量碳纳米管量子点的相互作用行为--一种“人造大分子”。%本提案是应“纳米科学与工程”(NSF-00-119)的征集而提交的。由此产生的拨款由材料研究、化学和物理部门共同资助。这项拟议的研究将在从纳米到微米的广泛空间尺度上研究模型和现实系统中的量子干涉(相干)和电子-电子相互作用(关联)。关联和相干的相互作用是当前化学和物理中最深入的主题之一。纳米结构为研究这些效应提供了一种新的受控环境：相互作用和干扰都可以通过改变纳米结构的大小和形状来操纵，从而直接获得关于它们相互作用的信息。首席研究员(PI)将计算从一纳米到一微米的几个典型案例中这种操纵的结果。此外，正在研究的一些远程技术在其操作中涉及电子-电子相互作用和量子干扰-例如，单电子学、自旋电子学、分子电子学和量子计算。PI计划调查这些可能的器件结构中的连贯性和相关性。因此，该项目将为评估这些新兴纳米技术的实际相关性所需的知识库作出贡献。

0103003BarangerThis 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.***