Superconductivity and magnetism at and above 38K in molecular materials

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Metals are used for electricity transmission, but energy is lost as heat because of electrical resistance. Superconductors have no electrical resistance and can carry electricity without losing energy, so finding superconductors which work at as high a temperature as possible is important. Most superconductors have simple structures built from atoms, but recently superconductors made from molecules arranged in regular solid structures have been found. Recent work by the proposing groups on molecular fulleride-based systems led to the discovery of the highest working temperature (at 38 K) for a molecular superconductor. We found that the electronic ground state which is in competition with superconductivity is magnetically ordered - this ordering also occurs at a very high temperature (46K) for a material where the active electrons are in orbitals of s/p parentage. We showed how the exact arrangement of the C60 molecules in the solid with stoichiometry Cs3C60 can be controlled to switch on the zero-resistance superconducting state from the insulating magnetically ordered state. In this project we will exploit the newly presented opportunities arising from these discoveries. We will identify the factors responsible for determining whether superconducting or magnetic ground states are adopted in new fulleride systems. We will develop new structural families of molecular, s/p electron-based superconductors and magnets with enhanced properties, controlled in an understandable manner by crystal symmetry, orbital degeneracy and lattice packing. In order to achieve this, we will use focussed solution-based synthetic protocols that we have pioneered, combined with structural and physical property measurements at ambient and high pressure and high-level electronic structure calculations. The project will explore unique aspects of the behavior of correlated electrons in solids i.e. electrons whose behavior is determined by their mutual Coulomb repulsion. This is one of the most important contemporary problems in condensed matter science. The high molecular and lattice symmetry of fullerene-based solids offers an opportunity to study strongly correlated electrons under conditions that are qualitatively different from previously studied materials, and therefore to take our understanding of molecular superconductivity and magnetism and the metal-insulator transition to an unprecedentedly advanced stage. The programme exploits the complementary expertise of the two principal investigators and will lead to a new generation of novel fullerene-based molecular materials with unpredictable and theoretically challenging properties.