New Directions in Molecular Superconductivity

The design of superconducting materials in order to achieve higher transition temperatures (Tc) to the zero-resistance state has been recognised by recent international and national reviews as at the extreme forefront of current challenges in condensed matter science with potential for transforming existing and enabling new technologies of tremendous economic and societal benefits in energy and healthcare. Achieving the zero-resistance state requires close control of the interactions of electrons with each other (known as electron correlation) and with lattice vibrations (phonons). This project addresses these challenges by building on EPSRC-supported collaborative work by the project team, which has shown that high Tc superconductivity, defined both in terms of transition temperature and the key role played by electronic correlations, is accessible in molecular systems. In the fullerene-based molecular superconductors, superconductivity occurs in competition with electronic ground states resulting from a fine balance between electron correlations and electron-phonon coupling in an electronic phase diagram strikingly similar to that of the atom-based copper oxide high Tc superconductors, where correlation plays a key role. A second molecular superconductor family with transition temperatures over 30 K, based on metal intercalation into aromatic hydrocarbons, has also been reported. It is therefore timely to optimise and understand superconducting materials made from molecules arranged in regular solid structures.

The scope of synthetic chemistry to tailor molecular electronic and geometric structure makes the development of molecular superconducting systems important, because this chemical control of the fundamental building units of a superconductor is not possible in atom-based systems. The molecular systems are the only current candidates for the important target of isotropic correlated electron superconductivity. We will exploit these opportunities by integration of new chemistry with new physical understanding, exemplified by revealing how changes in molecular-level orbital degeneracy driven by chemical control of molecular charge and overlap direct the electronic structure of an extended solid. We will develop the new chemistry of the molecular solid state that will be needed for this level of electronic structure control, in particular mastering the chemistry of metal intercalation into hydrocarbons. This new materials chemistry will include the use of new building blocks (such as endohedral metallofullerenes) and will harness the assimilation of defects to access new molecular packings, motivated by our discovery that different packings of the same molecular unit give different Tc and distinct electronic properties. Further structural control will be exercised by binding small molecules to the cations intercalated into the molecular lattices. The synthesis of metal-intercalated solids based on multiple molecular components will be undertaken to permit detailed optimisation of the electronic structure. We will thus specifically exploit the molecular system advantages of isotropy, packing and molecular-level electronic structure control by developing the new chemistry of the molecular solid state needed to establish the new electronic ground states.

Physical understanding of the structural and chemical origins of the new electronic states is essential to identify the factors controlling the electron pairing in the superconductors. This understanding will emerge from an integrated investigation of the insulator-metal-superconductor competition, spanning thermodynamic, spectroscopic and electronic property measurements closely linked to comprehensive structural work in order to produce the structure-composition-property relationships required for the design of next generation systems. The project benefits from an international multidisciplinary collaborative team to ensure all relevant techniques are deployed.

Superconducting materials have the potential to play a leading role in addressing current global priorities such as energy and the environment. This project aims to extend the realm of superconducting materials by the discovery of new systems and the understanding of superconducting pairing mechanisms. This may enable technological breakthroughs which are of major economic value to society. For instance, ordinary metals such as copper are used for electricity transmission, but energy is wasted as heat because of electrical resistance. Superconductors have no electrical resistance and can carry electricity without losing energy, so finding new superconductors with enhanced performance limits - working at as high a temperature as possible and reducing electrical losses as far as possible - is of paramount importance for power transmission. Large scale applications of suitable superconducting materials can make a major contribution to the energy problem by enhancing energy efficiency, optimising power grid transmission through fault current limiting and superconducting magnetic energy storage and assuring an environmentally benign energy infrastructure. The issue of sustainability is a serious one. Metals such as copper are running short and becoming increasingly expensive while China recently announced its decision to cut export quotas for rare-earth minerals, producing a doubling in rare earth prices. Many superconducting materials, including the iron-based and the high-Tc superconductors, contain arsenic or heavy scarce elements which are also toxic. Fundamental research targeting sustainable sources for functional materials (here, superconductors made of sustainably-sourced carbon-based components) is essential to meet these challenges. Achieving this goal requires the long-term fundamental research proposed here to synthesise materials with the required properties. Advances in superconductivity will impact other sectors e.g. healthcare through the magnets used in magnetic resonance imaging.

The project has specific mechanisms in place to disseminate outputs to UK industry. The Knowledge Centre for Materials Chemistry at Liverpool working closely with the Knowledge Transfer Partnerships Office at Durham and the Molecular Engineering Translational Research Centre will disseminate outputs to companies working in relevant sectors on a regular basis. A dissemination showcase event will be held to encourage dialogue between the industrial and academic communities and foster new ideas generation to enhance UK superconductivity research. Exploitable opportunities will be identified through regular meetings with the KT teams. Identified Intellectual Property which is thought to be commercially exploitable will be protected by the Universities through Durham's Business and Innovation Services and Liverpool's Business Gateway.

Engagement with society will be at many levels ranging from press releases of major research breakthroughs to unsolicited highlights of our research findings in both prestigious specialised and popular scientific publications to outreach events showcasing EPSRC-supported research to various stakeholders - policymakers, industrialists, local community and school children. The synergic involvement of both Institutions is highly beneficial here and will utilise established local initiatives such as Science Week and Celebrate Science at Durham and Schools Labs at Liverpool as well as nationwide engagement functions such as the House of Commons KCMC events.

Society will further benefit from the effective cross-disciplinary training in an international setting of collaborations and state-of-the-art facility usage of the two PDRA scientists who will master the challenges needed to address to make progress in the area of superconductivity. This will provide the UK with high quality workforce needed, both in academia and industry, to ensure that it remains highly competitive globally in a key scientific area.