The Role of Coulomb Interactions in Low Carrier Density, Disordered Sytems

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Experiments exploring itinerant magnetic and nearly magnetic states in low carrier density metals and semiconductors are the focus of this research program. Such materials are particularly sensitive to external magnetic fields as is apparent in their transport, magnetic, and thermodynamic properties. This sensitivity results from mechanisms unrelated to those found in the well studied local magnetic systems where carrier scattering can be controlled by magnetic fields. Instead, disorder, poor screening, and strong exchange interactions lead to surprisingly large and robust quantum interference effects. The control over carrier densities, disorder, and magnetic ground states that these materials offer, along with their sensitivity to magnetic fields, suggest that innovative device technologies may result from these investigations. Other experiments included in this program involve the exploration of many body effects in low dimensional systems such as bulk one-dimensional magnets and homogeneous ultra-thin films. This research involves undergraduate as well as graduate students and participants in the Teach For America program who obtain a full exposure to experimental science from the synthesis, characterization, and careful measurement of the materials, to the data analysis and publication of results. %%%Many of the new concepts for advanced electronic device design rely not only on the electronic carrier charge, but also on the carriers intrinsic angular momentum, or spin, as well. Much of the progress in realizing these novel technologies has been made in semiconducting and metallic systems where local magnetic moments, magnetic moments associated with the ions that make up the crystal lattice, are either intrinsic to the material or can be added as impurities. In this research program we are exploring magnetic systems where the magnetism and electrical conduction are due to the very same electrons in order to search for novel physical properties. These itinerant magnetic systems may offer greater control over both the magnetic and electronic attributes, which may allow innovative design technologies. The focus of this experimental program is the exploration of materials and mechanisms by which sensitivity to external parameters, and thus controls of physical properties occur. This research involves undergraduate as well as graduate students and participants in the Teach For America program who obtain a full exposure to experimental science from the synthesis, characterization, and careful measurement of the materials, to the data analysis and publication of results.