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内审查认为是凝聚态科学当前挑战的极端前沿，具有改变现有和使之成为可能的新技术的潜力，在能源和医疗保健方面具有巨大的经济和社会效益。要达到零电阻态，需要密切控制电子之间的相互作用(称为电子关联)以及与晶格振动(声子)的相互作用。该项目通过建立在EPSRC支持的项目组合作工作的基础上解决了这些挑战，该合作工作表明，在分子系统中可以获得根据转变温度和电子关联所起的关键作用定义的高超导电性。在富勒烯分子超导体中，超导性与电子基态竞争，这是由于电子关联和电子-声子耦合之间的精细平衡而产生的，在电子相图中与原子基氧化铜基高T_c超导体非常相似，其中关联起着关键作用。还报道了第二个分子超导体家族，其转变温度超过30K，基于金属嵌入芳香烃。因此，现在是优化和理解由规则固体结构的分子制成的超导材料的时候了。合成化学的范围定制分子的电子和几何结构使得分子超导系统的发展变得重要，因为这种对超导体基本构造单元的化学控制在基于原子的系统中是不可能的。分子体系是各向同性关联电子超导性这一重要靶标的唯一候选体系。我们将通过将新的化学与新的物理理解相结合来利用这些机会，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直接指导扩展的固体的电子结构。我们将开发分子固态的新化学，这将是这种电子结构控制所需的，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(如面体内金属富勒烯)，并将利用缺陷的同化来获得新的分子填充，这是由于我们发现同一分子单元的不同填充提供不同的T_c和不同的电子性质。进一步的结构控制将通过将小分子与嵌入到分子晶格中的阳离子结合来实现。将进行基于多分子成分的金属插层固体的合成，以允许对电子结构进行详细的优化。因此，我们将通过发展建立新的电子基态所需的新的分子固态化学，来具体地开发各向同性、堆积和分子级电子结构控制等分子系统的优势。了解新电子态的结构和化学起源对于确定控制超导体中电子配对的因素是至关重要的。这种理解将产生于对绝缘体-金属-超导体竞争的综合研究，包括与全面结构工作密切相关的热力学、光谱和电子性能测量，以产生设计下一代系统所需的结构-组成-性能关系。该项目得益于一个国际多学科协作团队，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.