Experimental Studies of Organic Crystals, Metals and Superconductors

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9976576ChaikinThis project uses a combination of magnetic fields, low temperatures, unusual materials, and novel lithographies to test some of the basic ideas of condensed matter physics. The Bechgaard salts (TMTSF)2 X (X=PF6, ClO4, etc.) are highly anisotropic electronic conductors, which exhibit many of the most interesting ground states in nature: metallic, superconducting, spin density wave, and quantum Hall effect. In addition, they show unique properties in a magnetic field where the magnetic length competes with the Fermi wave-vector to produce a cascade of phase transitions. These commensurability effects are also present in flux quantization experiments that are performed on patterned superconducting networks on a micron length scale, comparable to the coherence length. Similar coherent interference effects may occur in semiconductors and metals when patterned on the nanometer length scale. Our fabrication of patterns on this length scale, using diblock copolymers as lithographic masks opens up new possibilities for device experiments where the modulation potential is much smaller than the elastic mean free path.%%%The aim of this research is to make fundamental studies of electronic systems and the development of new cross-disciplinary techniques for using polymers to control electronic properties. Conventional lithography is presently limited to structures on the scale of tenths of microns whereas self-assembled polymers have spacings on a 5-50 nanometer scale. Diblock copolymers have been used by these researchers as lithographic masks to pattern semiconductors and metals at a density of trillions of structures on a 3-inch wafer. Studies will be made on the induced periodic structure to monitor their effect on the electronic properties of metals, semiconductors, and superconductors. Devices that may result from such studies include quantum dot lasers and ultra-dense memories. It is anticipated that some of the ways that electrons can adjust to periodic structures will be seen on the molecular level in the organic conductors where electrons form a charge density wave, and at the micron level where the magnetic flux locks into particular patterns on a superconducting grid. ***