New Directions in Molecular Superconductivity

超导材料的设计，以实现更高的转变温度（Tc）到零电阻状态，已被最近的国际和国家审查认可为在凝聚态科学当前挑战的极端前沿，具有改造现有和实现能源和医疗保健领域巨大经济和社会效益的新技术的潜力。实现零电阻状态需要密切控制电子之间的相互作用（称为电子相关）和晶格振动（声子）。该项目通过建立epsrc支持的项目团队的协作工作来解决这些挑战，该项目表明，从转变温度和电子相关所起的关键作用来看，高Tc超导性在分子系统中是可以实现的。在富勒烯基分子超导体中，超导性发生在电子基态的竞争中，这是由于电子相图中电子相关性和电子-声子耦合之间的微妙平衡，这与原子基氧化铜高Tc超导体的电子相图非常相似，其中相关性起着关键作用。另一个分子超导体家族，其转变温度超过30k，基于金属嵌入到芳烃中，也有报道。因此，优化和理解由排列在规则固体结构中的分子制成的超导材料是及时的。合成化学的范围是定制分子电子和几何结构，这使得分子超导系统的发展很重要，因为这种对超导体基本构建单元的化学控制在基于原子的系统中是不可能的。分子体系是目前唯一的候选各向同性相关电子超导的重要目标。我们将通过整合新的化学和新的物理认识来利用这些机会，例如揭示由分子电荷和重叠的化学控制驱动的分子水平轨道简并的变化如何指导扩展固体的电子结构。我们将发展分子固态的新化学，这将需要这种水平的电子结构控制，特别是掌握金属嵌入碳氢化合物的化学。这种新的材料化学将包括使用新的构建块（如内嵌金属富勒烯），并将利用缺陷的同化来获得新的分子填料，这是由于我们发现相同分子单元的不同填料具有不同的Tc和不同的电子性质。进一步的结构控制将通过将小分子与插入到分子晶格中的阳离子结合来实现。基于多种分子组分的金属插层固体的合成将进行，以允许详细优化电子结构。因此，我们将通过开发建立新的电子基态所需的分子固态的新化学，专门利用各向同性，填充和分子水平电子结构控制的分子系统优势。对新电子态的结构和化学起源的物理理解对于确定控制超导体中电子配对的因素至关重要。这种理解将从绝缘体-金属-超导体竞争的综合调查中产生，跨越热力学，光谱和电子特性测量，与全面的结构工作密切相关，以便产生下一代系统设计所需的结构-组成-特性关系。该项目受益于国际多学科合作团队，以确保部署所有相关技术。

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.