The Normal State and the Metal-Insulator Transition of High Critical Temperature Superconductors

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9501504 Lindenfeld The proposed research addresses the question to what extent and in what manner the occurrence and properties of the superconducting state of high-Tc materials are influenced by the continuing presence of properties related to the magnetic order of the insulating state. The compounds may be transformed from one state to the other by changes in the concentration of their constituent elements, by the addition of other elements, or by the application of high magnetic fields. Each of these paths will be followed, and a a variety of properties will be measured, with emphasis on the magnetoresistance over a wide range of temperatures. Aligned thin films of high-Tc materials will be prepared at Rutgers by pulsed laser deposition. Initial emphasis will be placed on lanthanum strontium copper oxide material that has led to the production of thin films with transition temperatures and other properties that are of particularly high quality. %%% The proposed research investigates the extent and manner in which the occurrence and properties of the low-temperature superconductivity of so-called "high-Tc" materials are influenced by the presence of properties related to the magnetic characteristics of the insulating form of the material. These compounds may be changed from insulator to superconductor by changes in the concentration of their constituent elements, by the addition of other elements, or by the application of strong magnetic fields. Each of these approaches will be investigated, and a variety of properties will be measured, with emphasis on the electrical resistance in the presence of an applied magnetic field (magnetoresistance). Thin films of high-Tc compounds prepared at Rutgers by pulsed laser deposition techniques will be studied, with initial emphasis on lanthanum strontium copper oxide, a material whose superconducting transition temperature and other propertie s are of particularly high quality. ***