Experimental Studies of Organic Charge Transfer Salts

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9626291 Chaikin A series of experiments are proposed to understand some of the basic properties of states of matter in organic conductors, and to gain insights into several current problems in condensed matter physics. For example, the Bechgaard salts are the only materials which exhibit the quantum Hall effect as a bulk three dimensional phenomenon. They are therefore unique systems for studying what happens when the conventional two dimensional electron gas layers are coupled. Questions as to the perpendicular conductivity and the coupling of edge states are open and testable. As superconductors these systems are at least as anisotropic as any others and they have much longer mean free paths. They are excellent candidates for investigating flux pinning, dynamics and Josephson vortices. Investigation also are proposed on the nature of the superconducting state. The magnetic field effects in both the"normal" metal and field induced spin density wave states have proven so unusual that there are a wealth of new phenomena to be explained. Coupled with the fact that questions of commensurability, magnetic breakdown, competing order parameters and frustration leave the limiting high field ground state an open question theoretically as well as experimentally, there is much to fuel continued excitement in this field. %%% This proposal is for continuation of a mostly experimental study of how low-dimensional strong interactions and frustration from applied fields act together to produce some quite interesting states of matter in organic conductors. The Bechgaard salts are among the most interesting electronic materials ever discovered. At room temperature they are highly anisotropic metals, but upon cooling they undergo a variety of transitions to a remarkable number of low temperature states. They were the first organic superconductors, but that is arguably their least interesting property. Depending on the anion and the pressure the ground states may be var ied from charge or spin density wave insulator to metal or superconductor. However, the properties discovered in moderate magnetic fields are even more unusual and striking. The normal metal phase also is extremely unusual showing angular dependent resonances and large magnetoresistances completely unexplainable from the known bandstructure.