NIRT: Computational Design and Optimization of Nanoscale Spintronic and Thermoelectric Devices

这项建议是为了响应纳米科学与工程倡议，NSF 01-157，纳米级跨学科研究团队(NIRT)。该奖项由材料研究部和国际部联合资助，乔治敦大学和IBM-Almden的研究人员参与了该奖项。该研究项目的目标是开发和应用计算方法来帮助优化自旋电子器件，并研究热电制冷器的新方案。这两种类型的器件都由堆叠在一起的不同材料的超薄层组成，形成了一个多相系统，在该系统中，通过界面的存在，在纳米尺度上强烈地改变了体属性。密度泛函方法和多体技术将结合起来研究这类系统的平衡和非平衡性质。自旋电子学项目旨在更好地理解如何有效地将金属自旋注入半导体。这个问题是改进的自旋晶体管和自旋过滤器设计的关键。计算机算法将被开发来自洽地计算由铁磁体、半导体、绝缘体和接近金属-绝缘体转变的材料组成的纳米级多层器件中的非平衡稳态输运。每个界面附近的电荷和自旋的重排将被自洽地处理。密度泛函方法将被用来评估特定材料的界面性质，如费米能级失配以及电荷和自旋散射长度，这些将被用作Keldysh非平衡输运代码的输入参数。在热电项目中，由金属、半导体和重费米子组成的纳米级异质结构以及其他强关联的材料将被作为潜在的热电器件进行研究。这是正在进行的块状材料热电和约瑟夫森结多体效应建模工作的延伸。数值重整化群将被用来研究周期Anderson模型及其与Falicov-Kimball模型组合所描述的系统的平衡性质。传输特性将使用线性响应形式来计算。密度泛函计算将被用来确定相关界面的性质并估计晶格模型的参数区域。到目前为止，实验上的困难阻碍了对由重费米子材料构建的纳米级设备的系统研究。所提出的计算模型将有助于指导寻找基于重费密子的新型低温热电器件。这种大学和行业的合作将为博士后研究人员和研究生提供宝贵的教育机会。这位乔治敦大学的研究生将在IBM现场工作一年，这是他/她在乔治敦大学工业领导物理项目中接受培训的一部分。博士后研究人员还将在学术和工业研究环境中获得经验。此外，该项目还涉及国际合作，特别是与克罗地亚的合作，高级和初级人员都将参与其中。%本提案是针对纳米科学和工程倡议，NSF 01-157，纳米级跨学科研究小组(NIRT)而提出的。该奖项由材料研究部和国际部联合资助，乔治敦大学和IBM-Almden的研究人员参与了该奖项。该研究项目的目标是开发和应用计算方法来帮助优化自旋电子器件，并研究热电制冷器的新方案。这两种类型的器件都是由不同材料的超薄层堆叠在一起形成的，形成了一个不同的系统，其中通过界面的存在在纳米尺度上对块状特性进行了强烈的修改。这种大学和行业的合作将为博士后研究人员和研究生提供宝贵的教育机会。这位乔治敦大学的研究生将在IBM现场工作一年，这是他/她在乔治敦大学工业领导物理项目中接受培训的一部分。博士后研究人员还将在学术和工业研究环境中获得经验。此外，该项目还涉及国际合作，特别是与克罗地亚的合作，高级和初级人员都将参加。

This proposal was received in response to the Nanoscale Science and Engineering Initiative, NSF 01-157, category Nanoscale Interdisciplinary Research Team (NIRT). The award is funded jointly by the Division of Materials Research and the International Division, and involves researchers at Georgetown University and IBM-Almaden.The objective of this research project is to develop and apply computational methods to help optimize spintronic devices and to investigate novel proposals for thermoelectric coolers. Both types of devices to be considered consist of ultrathin layers of different materials stacked together, forming a heterogeneous system in which bulk properties are strongly modified on the nanoscale by the presence of interfaces. Density-functional methods and many-body techniques will be combined to study both equilibrium and nonequilibrium properties of such systems. The spintronics project is aimed at developing a better understanding of how to efficiently inject spins from metals into semiconductors. This issue is key for the design of improved spin transistors and spin filters. Computer algorithms will be developed to self-consistently calculate the nonequilibrium steady-state transport in nanoscale multilayer devices composed of ferromagnets, semiconductors, insulators, and materials close to the metal-insulator transition. The rearrangement of charge and spin near each interface will be treated self-consistently. Density-functional methods will be employed to evaluate materials-specific interface properties such as fermi-level mismatch and charge and spin scattering lengths, which will then be used as input parameters for the Keldysh nonequilibrium transport codes.In the thermoelectric project, nanoscale heterostructures composed of metals, semiconductors, and heavy-fermion, and other strongly-correlated, materials will be investigated as potential thermoelectric devices. This is an extension of ongoing work on thermoelectricity in bulk materials and on modeling many-body effects in Josephson junctions. The numerical renormalization group will be used to examine equilibrium properties of systems described by the periodic Anderson model and its combination with the Falicov-Kimball model. Transport properties will be calculated using a linear response formalism. Density-functional calculations will be used to determine properties of relevant interfaces and to estimate parameter regimes for the lattice models. To date, experimental difficulties have thwarted a sytematic study of nanoscale devices constructed from heavy-fermion materials. The proposed computational modeling will help guide the search for novel heavy-fermion-based-low-tempreature thermoelectric devices.This university-industry collaboration will provide valuable educational opportunities for postdoctoral researchers and graduate students. The Georgetown graduate student will spend one year at the IBM site as part of his/her training in Georgetown's Industrial Leadership in Physics program. Postdoctoral researchers will also gain experience in both the academic and industrial research environments. In addition, the project involves international collaborations, particularly with Croatia, in which both senior and junior personnel will participate.%%%This proposal was received in response to the Nanoscale Science and Engineering Initiative, NSF 01-157, category Nanoscale Interdisciplinary Research Team (NIRT). The award is funded jointly by the Division of Materials Research and the International Division, and involves researchers at Georgetown University and IBM-Almaden.The objective of this research project is to develop and apply computational methods to help optimize spintronic devices and to investigate novel proposals for thermoelectric coolers. Both types of devices to be considered consist of ultrathin layers of different materials stacked together, forming a heterogeneous system in which bulk properties are strongly modified on the nanoscale by the presence of interfaces.This university-industry collaboration will provide valuable educational opportunities for postdoctoral researchers and graduate students. The Georgetown graduate student will spend one year at the IBM site as part of his/her training in Georgetown's Industrial Leadership in Physics program. Postdoctoral researchers will also gain experience in both the academic and industrial research environments. In addition, the project involves international collaborations, particularly with Croatia, in which both senior and junior personnel will participate.***