Experimental Studies of Organic Crystals, Metals and Superconductors

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This condensed matter physics project describes novel investigations of dense, strongly interacting electron systems. These organic conductors are of primary interest because of the variety of ground states that they display. Materials such as (TMTSF)2PF6, a Bechgaard salt, have served as an exciting laboratory for these fundamental studies. They exhibit almost all of the condensed electronic phases discovered in other materials, and some new ones. (TMTSF)2PF6 is metallic, insulating, semi-metal, semi-conducting, superconducting, spin and charge density wave, one, two or three dimensional, with a Field Induced Spin Density Wave (FISDW) state that exhibits the quantum Hall effect (QHE) in bulk, and both Fermi liquid and non-Fermi liquid behavior as temperature, pressure and magnetic field are varied. However, there are still basic questions which remain and which are at the heart of the correlated electron problem. The nature of the metallic and superconducting states, dimensional crossover, commensurability, competition between the many ground states and the effects of applied fields are just beginning to be understood. This research involves training graduate and undergraduate students in the use of high magnetic fields, high pressures, low temperatures and a variety of techniques including transport, NMR, magnetic and thermodynamic measurements. This training prepares students for careers in industry, academe, or government.This project investigates the microscopic interactions responsible for the electronic properties of materials. The experiments should lead to a better understanding of how to make metals, insulators, magnets, and superconductors. The materials are mostly organic crystals chosen for their potential ease of fabrication and their mechanical properties but also for their variability and control. A goal is to answer fundamental questions about how the structure of the crystals, with chain like stacking of the flat molecules and hence quasi-one dimensional behaviors, influences the electron conduction mechanism and the ability of the electrons to avoid each other. The repulsion between the electrons and their self-avoidance is responsible for the different states found in these crystals: antiferromagnet, Quantum Hall conductor, superconductor, and a host of insulating phases. In direct contact with high school students and through the Princeton Materials Institute programs we encourage research and visits to our labs by K-12 students. Our work involves the extensive training of undergraduates, graduate students and postdocs in state of the art measurement and fabrication techniques, from nanolithography to high pressure, high magnetic field and low temperature experiences. This training prepares students for careers in industry, academe, or government.