New correlated electronic states arising from strong spin-orbit coupling

Magnetic phenomena pervade the world around us and are used in a huge variety of practical devices, ranging from nanoscale data storage devices through electric motors to plasma fusion reactors. At a fundamental level, magnetism in solids comes from the coordinated actions of many atomic magnets. The atomic magnetism originates from the intrinsic spin and the orbital motion of the electrons, and the relative importance of spin and orbital magnetism depends on the particular magnetic atom and its environment.

This project concerns magnetism in oxides containing heavy metal atoms such as ruthenium, molybdenum, osmium and rhenium. These atoms have partially filled 4d or 5d electronic orbitals with a large spin-orbit interaction which strongly entwines the spin and orbital magnetism. Until recently, the study of magnetism in the presence of strong spin-orbit coupling was confined to f-electron systems, but today there is increasing focus on 4d and 5d systems, in which the greater mobility of the electrons results in a more diverse range of phenomena.

In the past few years, a large number of theoretical predictions have appeared for magnetic systems with strong spin-orbit coupling, but very few have been confirmed empirically. The predictions include: (i) materials whose atoms have no magnetism when in isolation but develop magnetism through interactions with neighbouring atoms, (ii) anisotropic, bond-directional magnetic couplings resulting in novel propagating magnetic modes, (iii) quantum-mechanically entangled spin and orbital liquid states with exotic emergent quasiparticle excitations, (iv) metal-insulator transitions driven by spin-orbit enhanced magnetic correlations, and (v) unconventional superconductivity of doped electrons mediated by magnetic fluctuations.

The programme of research aims to search for and study these and other novel magnetic phases in 4d and 5d oxides. A significant challenge will be the growth of high quality single crystals, which are essential as samples for the experiments. To overcome this challenge we have assembled two leading crystal growers with a vast amount of relevant expertise, as well as a Project Partner, Prof Yamaura, who brings additional capability in high pressure synthesis. We shall perform measurements to probe the novel spin-orbital states in the materials of interest using state-of-the-art techniques at international synchrotron and neutron facilities. We shall collaborate with staff at the facilities, including our Project Partners the Diamond Light Source and Paul Scherrer Institute, as well as the European Synchrotron Radiation Facility in Grenoble and the ISIS spallation neutron source, to perform the measurements and develop the necessary techniques. Finally, we shall work with our theory Project Partners at the University of Toronto and collaborators to develop a detailed understanding of the new electronic and magnetic states we will uncover.

Beyond the academic community, the research will have an impact on

1) Existing and future industries, particularly those that exploit emerging functional materials, such as magnetic, spintronic and superconducting materials, and future electronic devices that aim to exploit Mott physics. Discovery research of the kind we are proposing provides the fuel from which new functional materials and phenomena are developed and subsequently translated into technologies. This type of impact is not likely to be felt in the short term, and is difficult to predict, but the correlated behaviour of compounds containing 4d and 5d electrons which we will investigate could well form the basis for materials which have desirable properties for applications. Oxides, in particular, are attractive for applications because of their stability under typical device operating conditions.

A more immediate way in which industry will benefit is through the supply of skilled scientific personnel. The post-docs and graduate students directly involved with the research will receive a broad training in research techniques, scientific communication, project planning and team-working, all of which are transferrable skills should they choose to pursue a career outside academia.

2) Intellectual culture in society. The general public is fascinated by science, especially younger members of society, as can be seen from the popularity of science communicators such as Jim Al-Khalili and Brian Cox. Effective communication of fundamental science is important for inspiring the next generation of scientists, and also for educating the wider public about the benefits and risks associated with science and technology, for example in the process of climate change. In addition to conventional academic dissemination routes we are committed to a wider spectrum of public awareness and outreach activities through our institutions which provide a vehicle to communicate any important new discoveries arising from the research to the public.

3) Large-scale condensed matter facilities. The research will make extensive use of national and international facilities for neutron and synchrotron X-ray research, such as the Diamond Light Source, ISIS Facility, European Synchrotron Radiation Facility, the Institut Laue-Langevin and the Paul Scherrer Institute. Many of the experiments will be challenging, for example through having signals of interest which are very weak or difficult to interpret, or could require developments such as new ways to exploit beam polarisation or sample environments. Our close engagement with facilities through our Project Partner agreements and other links will facilitate technique developments which will benefit the facilities and all their users, including users from industry and other non-academic groups.