New Directions in Molecular Superconductivity

为了实现更高的转变温度（Tc）到零电阻状态而设计超导材料已被最近的国际和国家审查认为是凝聚态科学当前挑战的最前沿，具有改造现有技术和实现新技术的潜力能源和医疗保健领域的巨大经济和社会效益。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）。该项目通过建立在EPSRC支持的项目团队的合作工作来解决这些挑战，该项目表明，在转变温度和电子相关性所起的关键作用方面定义的高Tc超导性在分子系统中是可访问的。在基于富勒烯的分子超导体中，超导性发生在与电子基态的竞争中，这是由于电子相图中电子相关性和电子-声子耦合之间的精细平衡，与基于原子的氧化铜高Tc超导体惊人地相似，其中相关性起着关键作用。第二个分子超导体家族的转变温度超过30 K，基于金属嵌入到芳烃，也有报道。因此，优化和理解由分子排列成规则固体结构的超导材料是及时的。合成化学的范围可以定制分子的电子和几何结构，这使得分子超导系统的发展非常重要，因为这种对超导体基本构建单元的化学控制在原子系统中是不可能的。分子系统是目前唯一的候选者的重要目标的各向同性相关电子超导性。我们将利用这些机会，通过整合新的化学与新的物理理解，例如揭示如何在分子水平的轨道简并的变化驱动的化学控制的分子电荷和重叠直接扩展固体的电子结构。我们将开发这种电子结构控制水平所需的分子固态的新化学，特别是掌握金属嵌入碳氢化合物的化学。这种新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包装，这是由于我们发现相同分子单元的不同包装会产生不同的Tc和不同的电子特性。进一步的结构控制将通过将小分子结合到插入分子晶格的阳离子上来实现。将进行基于多个分子组分的金属插层固体的合成，以允许电子结构的详细优化。因此，我们将具体开发的各向同性，包装和分子水平的电子结构控制的分子系统的优势，通过开发新的化学的分子固态需要建立新的电子基态。物理理解的结构和化学起源的新的电子状态是必不可少的，以确定在超导体中的电子配对的控制因素。这种理解将出现从绝缘体-金属-超导体竞争的综合调查，跨越热力学，光谱和电子性能测量密切相关的全面的结构工作，以产生下一代系统的设计所需的结构-成分-性能的关系。该项目受益于一个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.