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

Georgetown University, Washington DC

Investigators

Abstract

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. ***