A New Paradigm for Quantum Materials Discovery: S = 1/2 Kagome Magnets in the Two-Dimensional Limit

Materials research over the past century has had a phenomenal impact on modern-day life. Without materials discovery and the development of a fundamental understanding of the properties of solids, we would lack the many advanced technologies we have come to rely on today. A crucial challenge to enabling the technologies of tomorrow is to discover new classes of materials with never-before-seen properties that push the limits of our understanding of the physical world and that we can harness for societal and economic benefit.

Two related examples of emerging classes of materials that can display unprecedented behaviour are quantum materials and two-dimensional materials. Quantum materials are those whose properties are uniquely determined by quantum mechanical effects that remain evident at high temperatures and long length scales. The exotic properties of quantum materials are essential from a technological perspective as they will underpin the development of next-generation quantum technologies, such as quantum computing, over the 21st Century. Equally, the recent discoveries of two-dimensional materials demonstrate the extraordinary physical properties that can arise in matter when downscaled to atomically thin layers from the three-dimensional bulk. A well-known example is graphene, a two-dimensional form of carbon, which displays remarkable conductivity, flexibility and strength, holding great promise for novel device applications in the future.

This proposal aims to develop a new class of two-dimensional quantum materials that will unite concepts at the frontiers of materials chemistry and condensed matter physics. In particular, this study centres on a novel chemical paradigm for the quantum kagomé magnet, a cornerstone of current quantum materials research. In theory, the quantum kagomé magnet is a two-dimensional array of corner-sharing triangles of S = 1/2 magnetic moments that arise, for example, from the unpaired electrons of a transition metal ion such as copper. These ingredients conspire to give rise to an exciting assortment of quantum mechanical effects pertinent to future advanced technologies. As such, the realisation of different examples of quantum kagomé magnets is a crucial materials discovery challenge in order to explore and exploit their enigmatic physical properties experimentally. Since a revolutionary materials discovery in 2005, the research effort in this field has focussed heavily on the synthesis of inorganic materials which contain quasi-two-dimensional approximations of a quantum kagomé network. While this approach has unveiled some fascinating materials properties, it is ultimately limited by a fundamental need to vastly improve our control of materials design at the atomic level to truly understand the experimental signatures intrinsic to the quantum kagomé magnet.

To address this need, this research will first explore our ability to control the assembly and ensuing properties of a family of magnetic hybrid framework materials known as metal-organic frameworks; materials composed of inorganic copper-based magnetic kagomé layers connected via carbon-based organic molecules. The research will then go on to investigate a variety of promising routes to delaminate these materials and produce unique realisations of the quantum kagomé magnet in the two-dimensional limit. In the short-term, this project will deliver new understanding in quantum materials design and synthesis and a step-change in the available chemical realisations of quantum kagomé magnets. In the longer-term, the chemical nature of the targeted materials coupled with their strong propensity to manifest unconventional physics may have far-reaching implications in diverse fields, from condensed matter theory to magnetic property measurement and device fabrication.

To summarise project impact in the themes of economy, society, people and knowledge:

Economy - this project will deliver a new family of two-dimensional quantum magnetic materials synthesised at room temperature, which have the potential to manifest strong electronic correlations, quantum entanglement and topological order. Advancing our ability to synthesise and understand the structure-property relationships of such quantum materials is essential to move towards targeting specific functions for the development of next-generation quantum technologies [Nature Mater. 16, 1077 (2017)]. The commercialisation of quantum technologies is in its infancy globally, and so there is an opportunity for the UK to develop a competitive edge with support from UKRI and organisations such as the Compound Semiconductor Applications and High Value Manufacturing Catapults. The demonstration of an atomically thin quantum kagomé magnet produced via solution-processable methods would open wholly unique means to study and exploit the fascinating emergent properties of this highly-prized class of quantum matter and with it, possible routes to device integration and application of appeal to the growing quantum technologies market. As such, the results of this project will continue to strengthen the UK's position as a leader in quantum materials discovery, which forms the vital foundations for longer-term economic impact in quantum technology delivery.

Society - the potential for strong interplay between quantum materials discovery and capturing the emergent properties of quantum matter for new advanced technologies also holds great promise to enhance the quality of life in the 21st Century. As a 2017 article in The Economist [Subatomic opportunities: Quantum leaps] notes on the possible social impact of quantum research "for much of the 20th Century quantum has, in the popular consciousness, simply signified weird. In the 21st, it will come to mean better." With the ubiquitousness of digital information in the present day, the prospects for quantum spin systems, such as those targeted in this project, to provide low-power, energy-efficient and topologically-protected computation may enable unprecedented levels of global connectivity and information security to enrich further the ways in which we can interact and communicate. Of course, it is vital that this is achieved responsibly, and that society remains informed of the scientific advances that may underpin such remarkable technologies through clear and accurate public engagement.

People - the proposed research offers considerable professional development and training opportunities for both the PDRA and PI as well as associated researchers, such as PhD and undergraduate project students. The technical and interpersonal skills developed by these early-career researchers will make them highly valuable to future UK employers, in industrial research and development and higher-education sectors.

Knowledge - by complementing quantum materials synthesis with advanced characterisation and materials modelling this research will produce new knowledge and methodology of broad scientific appeal from functional materials chemistry to theoretical condensed matter physics. The knowledge outputs from this project set the pathway to a longer-term programme of research for the PI, as well as three key UK collaborations between early-career researchers working across materials synthesis, modelling and measurement. The interdisciplinary knowledge generated from this research aligns well with EPSRC's strategic focus for exploring opportunities outside the immediate research area of magnetic materials within its Physical Sciences theme, as well as addressing their recently identified Grand Challenges of both quantum physics for new quantum technologies and the nanoscale design of functional materials.