This award was made on a 'small' category proposal submitted in response to the ITR solicitation, NSF-02-168. It supports computational and theoretical research on complex nanostructures. Some compounds tend to spontaneously form complex spatially inhomogeneous electronic states on the nanoscale. Examples include high temperature superconductors, colossal magnetoresistive manganites, and dilute magnetic semiconductors. The PIs will explore the origins of the nanocluster generation phenomenon in a variety of compounds using a simplified framework provided by spin-fermion models. These models contain charge carrier and localized spin degrees of freedom; classical phonons may also be included. Research involves a careful computational effort to capture the percolating characteristics of the phenomenon and to elucidate the nature of complex inhomogeneous electronic ground states. Researchers using currently available algorithms have been able to unveil amazingly rich structures in these models, but further progress is difficult due to severe cluster-size and CPU limitations. The PIs will further develop algorithms for spin-fermion Hamiltonians to enable access to system sizes large enough so that magnetic and transport properties can be reliably calculated in percolative nanostructures. This research will emphasize the similarities among different materials and will help to relate investigations in different fields that use similar spin-fermion-like models. An aspect of this work involves modification of an algorithm from the computational lattice-gauge-theory community in high-energy physics. Codes developed in the course of this work will be made available to the broader materials theory community. This award supports broad educational experiences in computational science and physics for graduate students and educational experiences in physics for K-12 students. It also supports efforts to broaden participation of underrepresented groups in science. The research uses computation to advance fundamental theoretical condensed matter physics at the scientific frontiers. %%% This award was made on a 'small' category proposal submitted in response to the ITR solicitation, NSF-02-168. It supports computational and theoretical research on complex nanostructures. As a consequence of electronic correlations, some compounds tend to spontaneously form complex spatially inhomogeneous electronic states on the nanoscale. Examples include high temperature superconductors, colossal magnetoresistive manganites, and dilute magnetic semiconductors. The PIs will explore the origins of spatially inhomogeneous electronic states using spin-fermion models. These models focus on charge carriers, localized spins, and their interactions. Research involves a careful computational effort to elucidate the nature of complex inhomogeneous electronic ground states. Researchers using currently available algorithms have been able to unveil amazingly rich structures in these models, but further progress is difficult due to severe cluster-size and CPU limitations. The PIs will further develop algorithms for spin-fermion models to enable reliable calculations of magnetic and transport properties for percolative nanostructures. This research will emphasize the similarities among different materials and will help to relate investigations in different fields that use similar spin-fermion-like models. An aspect of this work involves modification of an algorithm from the computational lattice-gauge-theory community in high-energy physics. Codes developed in the course of this work will be made available to the broader materials theory community. This award supports broad educational experiences in computational science and physics for graduate students and educational experiences in physics for K-12 students. It also supports efforts to broaden participation of underrepresented groups in science. The research uses computation to advance fundamental theoretical condensed matter physics at the scientific frontiers. ***
