New Directions in Molecular Superconductivity

Lead Research Organisation: University of Liverpool
Department Name: Chemistry


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.


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Description We have identified a new state of matter, the Jahn-Teller metal, as the key electronic state responsible for unconventional superconductivity in the alkali metal fullerides. This demonstrates the control of an extended electronic state (the metallic state) by the electronic structure of a molecule.
We have found the superconductors with the highest critical fields known for three-dimensional structures.
We have identified the first structures reported in the field on metal (phen) acenes, a key advance for this field where superconductivity was reported in 2010, but until our work no crystal structures were known. This is essential information to place the entire field on a firm basis where properties can be linked to crystal structure and chemical composition.
Although we have not identified any superconductors, a quantum spin liquid ground state is displayed in an open shell organic-based material for the first time. The new metal-hydrocarbon chemistry we have developed is reported in two back-to-back Nature Chemistry papers. We have understood how to control the reaction conditions to avoid the chemically-driven decomposition of the hydrocarbon molecule while allowing the formation of the metal-hydrocarbon solids, which opens up a new set of opportunities for the synthesis of open-shell organic molecular materials beyond the C60 intercalation compounds.
Exploitation Route The advantage of molecular over atomic constituents of superconducting materials is that their electronic structures can be tailored by chemical synthesis. The identification of the molecular electronic feature that controls the unconventional superconductivity in these materials, in this case the orbital degeneracy of the C60 molecule (three electronic states in the molecule have the same energy) will allow the identification of new molecules as targets for synthesis in the quest for new superconducting materials, as their electronic structure can be expected to influence directly the electronic properties of the resulting extended solid. The observation of very high critical fields will enable new design motifs for three-dimensional superconducting systems. The four new metal (phen)acene solids are the first of this class of material to be isolated and studied. One of them displays a three-dimentional quantum spin liquid ground state, of interest for the development of new approaches to information storage. By further expanding this class of materials beyond the first four examples, we have shown in general how to allow the formation of these metal-hydrocarbon solids without chemical decomposition of the hydrocarbon, opening up a new field for study based on electron transfer to organic molecules.
Sectors Chemicals,Electronics,Energy,Transport

Description The identification of unsaturated hydrocarbons likely to form intercalation compounds of the type studied in this project has led to the development of machine-learning models to predict the formation of unsaturated cocrystals. The broad impact of these models for organic materials has formed the topic of several discussions with companies, informing their own internal data science strategies. The development of these models is directly attributable to the science developed in this project.
First Year Of Impact 2019
Sector Chemicals
Impact Types Economic

Description Prof Rosseinsky gave an invited talk at Knowledge Centre for Materials Chemistry Industrial Steering Group meeting, Birmingham, 28 November 2019 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Industry/Business
Results and Impact Presented on the topic of "Digital Materials Research and Innovation at the Materials Innovation Factory"
Year(s) Of Engagement Activity 2019
Description Prof. Rosseinsky gave an invited lecture at Quantum Materials Synthesis 2018 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Talk on New approaches to the discovery of inorganic materials and interfaces, for the dissemination of results for academic discussion
Year(s) Of Engagement Activity 2018
Description Prof. Rosseinsky gave an invited lecture at UKSR50 - 50 years of Synchrotron Radiation in the UK and its global impact, 2018 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Presentation on "Design of advanced materials? The importance of knowing where the atoms are.", for the dissemination of results for academic discussion
Year(s) Of Engagement Activity 2018