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

该提案是响应纳米科学与工程计划，NSF 01-157，纳米跨学科研究小组（NIRT）类别而收到的。该奖项由材料研究部门和国际部门联合资助，涉及乔治城大学和ibm阿尔马登的研究人员。本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，并研究热电冷却器的新方案。这两种类型的器件都是由堆叠在一起的不同材料的超薄层组成的，形成了一个非均质系统，其中通过界面的存在，在纳米尺度上强烈地改变了体性能。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。这个问题是改进自旋晶体管和自旋滤波器设计的关键。计算机算法将被开发来自一致地计算由铁磁体、半导体、绝缘体和接近金属-绝缘体过渡的材料组成的纳米多层器件中的非平衡稳态输运。每个界面附近电荷和自旋的重排将被自洽处理。密度泛函方法将用于评估材料特定的界面特性，如费米能级失配、电荷和自旋散射长度，这些将被用作Keldysh非平衡输运码的输入参数。在热电项目中，由金属、半导体、重费米子和其他强相关材料组成的纳米异质结构将被研究作为潜在的热电器件。这是对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。数值重整化组将用于检查由周期Anderson模型及其与Falicov-Kimball模型的组合所描述的系统的平衡特性。输运性质将使用线性响应形式来计算。密度泛函计算将用于确定相关界面的性质和估计晶格模型的参数制度。迄今为止，实验上的困难阻碍了对由重费米子材料构成的纳米级器件的系统研究。提出的计算模型将有助于指导寻找新的基于重费米子的低温热电器件。这种校企合作将为博士后研究人员和研究生提供宝贵的教育机会。乔治敦大学的研究生将在IBM工作一年，这是他/她在乔治敦大学工业物理领导力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，该项目涉及国际合作，特别是同克罗地亚的合作，高级和初级人员都将参加。该提案是在纳米科学与工程计划（NSF 01-157）类别纳米跨学科研究小组（NIRT）的响应中收到的。该奖项由材料研究部门和国际部门联合资助，涉及乔治城大学和ibm阿尔马登的研究人员。本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，并研究热电冷却器的新方案。这两种类型的器件都是由堆叠在一起的不同材料的超薄层组成的，形成了一个非均质系统，其中通过界面的存在，在纳米尺度上强烈地改变了体性能。这种校企合作将为博士后研究人员和研究生提供宝贵的教育机会。乔治敦大学的研究生将在IBM工作一年，这是他/她在乔治敦大学工业物理领导力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，该项目涉及国际合作，特别是与克罗地亚的合作，其中高级和初级人员都将参与

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.***