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

该提案是响应纳米科学与工程倡议，NSF 01-157，类别纳米跨学科研究小组（NIRT）。 该奖项由材料研究部和国际部共同资助，涉及乔治敦大学和IBM Almaden的研究人员。该研究项目的目标是开发和应用计算方法，以帮助优化自旋电子器件，并研究热电冷却器的新方案。 这两种类型的器件都是由不同材料的多层堆叠在一起组成的，形成了一个异质系统，在这个系统中，由于界面的存在，本体特性在纳米尺度上发生了强烈的变化。 密度泛函方法和多体技术将被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了解如何有效地将金属自旋注入半导体。 这个问题是设计改进的自旋晶体管和自旋滤波器的关键。 将开发计算机算法，以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新排列将自洽地处理。 密度泛函方法将被用来评估材料特定的界面特性，如费米能级失配和电荷和自旋散射长度，然后将被用作输入参数的Keldysh非平衡输运codes.In热电项目，纳米异质结构组成的金属，半导体和重费米子，和其他强相关的材料，将被调查作为潜在的热电器件。 这是一个正在进行的工作，在散装材料热电和约瑟夫森结的多体效应建模的延伸。 数值重整化群将被用来检查由周期性安德森模型及其与Falicov-Kimball模型的组合描述的系统的平衡性质。 输运性质将使用线性响应形式主义计算。 密度泛函计算将用于确定相关接口的属性，并估计参数制度的晶格模型。 到目前为止，实验上的困难阻碍了对由重费米子材料构成的纳米器件的系统研究。 所提出的计算模型将有助于指导新的重费米子基低温热电器件的研究。这种大学与工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。 乔治城大学的研究生将在IBM工厂工作一年，作为他/她在乔治城大学物理学项目中的工业领导力培训的一部分。 博士后研究人员还将获得学术和工业研究环境的经验。 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。该提案是响应纳米科学与工程倡议，NSF 01-157，类别纳米跨学科研究小组（NIRT）。 该奖项由材料研究部和国际部共同资助，涉及乔治敦大学和IBM Almaden的研究人员。该研究项目的目标是开发和应用计算方法，以帮助优化自旋电子器件，并研究热电冷却器的新方案。 这两种类型的器件都是由不同材料的多层堆叠在一起，形成一个异质系统，在这个系统中，界面的存在会在纳米尺度上强烈地改变本体特性。这种大学与工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。 乔治城大学的研究生将在IBM工厂工作一年，作为他/她在乔治城大学物理学项目中的工业领导力培训的一部分。 博士后研究人员还将获得学术和工业研究环境的经验。 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.***