2019 Nevill Mott Medal and Prize
Professor Stephen Hayden for pioneering studies of spin and charge excitations in cuprate superconductors and other strongly correlated electron systems.
Stephen Hayden is a world-renowned experimental physicist distinguished for use of novel neutron scattering techniques in studying collective magnetic excitations in superconductors and other strongly correlated electron materials. He has made groundbreaking measurements on high temperature cuprate, iron-based and heavy-fermion superconductors. His work has had lasting impact, making major contributions to the theoretical understanding of the systems investigated.
Hayden has made seminal discoveries in the field of high-temperature cuprate superconductors throughout his career. His progressive work has revealed, with every greater detail, how the structure and strength of the spin excitations in these materials vary across their doping-temperature phase diagram. Key findings are that the excitations in the superconducting compositions are highly structured and the spin waves in the antiferromagnetic parent are unconventional, unbinding into spinon pairs for certain wavevectors. The results provide definitive evidence for the high-energy excitations required by magnetically mediated theories of high temperature superconductivity.
Hayden's work on charge order in cuprate superconductors has also been highly influential. His groups' results have shown the detailed structure of the charge density waves and importantly how they interact with superconductivity as the latter is tuned with high magnetic field. It has been suggested that this charge order could play an important role in the mechanism of high temperature superconductivity.
Significant advances have also been made in studies of other strongly correlated materials, in particular the ruthenates. In Sr3Ru2O7, measurements led by Hayden, revealed the existence of a field-induced spin-density wave. This answers the question regarding the nature of the field induced quantum critical nematic state in this material. This has been a model system for studying electronic nematic order which now has applications in many other systems, including iron-based and cuprate superconductors.