Physics of Proximate Metallic and Insulating Phases

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**** NON-TECHNICAL ABSTRACT ****This project will pursue experiments to fabricate and characterize materials in which metals and insulators are in close proximity. The proximity of metallic and insulating phases in a given material arises in two ways: both phases simultaneously coexist and compete with each other, or one dominant phase can be transformed to the other. In both cases the change of an external parameter such as temperature or magnetic field can induce metal-insulator transitions accompanied by pronounced changes in electrical properties. The materials chosen for study include ultra thin disordered ferromagnetic films which can be tuned through a metal-insulator transition, complex oxides which comprise competing ferromagnetic metal and insulating phases, doped graphite which exhibits highly metallic/insulating behavior parallel/perpendicular to the carbon planes, and "topological insulators", which by virtue of their unusual electronic structure have conducting edge and surface states coexisting with insulating interiors. Understanding the results of these studies promises to unveil important new physics that will drive the design of novel composite metal-insulator materials that may be important for new technologies for the benefit of society. The research and education/outreach activities supported by this proposal will lead to the placement of graduate and undergraduate students in satisfying and productive professional careers within academic, industrial or government settings.**** TECHNICAL ABSTRACT ****This project will pursue experiments to fabricate and characterize materials in which metallic and insulating phases are in close proximity, thereby giving rise to complex and novel phenomenology. The materials chosen for study focus on four classes: (1) ultra thin ferromagnetic films that can be tuned through a metal-insulator transition by varying the disorder strength; (2) mixed phase manganites in which there is a temperature, strain and field-dependent competition between coexisting metallic and insulating phases near an insulator-metal percolation transition; (3) graphite in which there is an intercalation-induced in-plane "supermetallic" conductivity simultaneously appearing with an out-of-plane insulating conductivity; and (4) topological insulators, which by virtue of their unusual electronic band structure have conducting edge and surface states coexisting with insulating interiors. Understanding the results of these studies promises to unveil important new physics that will drive the design of novel composite metal-insulator materials at nanoscale dimensions under the unifying theme of proximate metallic and insulating phases. The associated research and education/outreach activities of this research will lead to the placement of graduate and undergraduate students in satisfying and productive professional careers within academic, industrial or government settings.