Molecular Organic Conductors: Triplet Superconductivity and Novel Angular Magnetoresistance Effects

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This individual investigator award supports an experimental project to investigate organic superconductors. One goal of this project is to determine the pairing symmetry in the quasi-one dimensional TMTSF superconductors, which a growing body of evidence suggests to be spin triplet in nature. A novel sample preparation technique will be employed to facilitate tunnel junction experiments aimed at measuring the energy gap and its anisotropy in momentum space, an essential quantity that has avoided detection for almost a quarter of a century. The goal is to determine which type of triplet state describes the pairing in these materials, p- or f-wave. This will be done via conductance measurements in a 10 mK, 13 kbar, 13 T, (temperature, pressure, magnetic field) environment. Another goal is to test a new "interference commensurate" model for the angular magnetoresistance oscillations seen in the normal metal state of the TMTSF conductors. In this model, for specific sample orientations in a magnetic field, quantum interference effects between electron waves in neighboring Brilluoin zones contribute to the electrical conductivity, and lead to novel changes of dimensionality. These experiments will also employ a 45T pulsed field magnet. The project will promote student learning and discovery of the physics of novel materials at several levels, high school, undergraduate, and graduate, through summer internships, fellowships and workshops.Magnetism is known to be the archenemy of superconductivity. This is one limitation on the resolution of MRI instruments, for example, which employ superconductors to generate strong magnetic fields. But what if it were possible to discover a route to detente between these rivals? In this project, evidence for the existence of a special form of superconductivity known as "spin triplet", in conjunction with an observed imperviousness of superconductivity to magnetism, will be sought in certain molecular organic conductors. These are among the most interesting electronic materials in our world, showing nearly every possible conducting property known: superconductor, metal, semiconductor, insulator, all in the same specimen. If they can be proven to be spin triplet (a rare, perhaps even unprecedented occurrence in nature), an important mechanism by which magnetism suppresses superconductivity will be taken away, allowing researchers to dream of schemes toward capitalizing on superconductivity's newfound immunity from magnetism. The project will promote student learning and discovery of the physics of such novel materials at several levels, high school, undergraduate, and graduate, through summer internships, fellowships and workshops.