This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
This award supports theoretical research and education focused mainly on the light elements, including hydrogen under conditions of high pressure and high temperature. The PI aims to elucidate quantum orderings, both in hydrogen and in hydrogen alloyed with other light element systems. Of increasing prominence in these systems is the enduringly fundamental and pragmatic area of superconductivity, impelled by the recent and quite dramatic discovery of superconductivity occurring in the metallic state of silane. That this could be a possibility was already raised in research supported by the previous grant and companion predictions that the hitherto 'simple' elements would adopt structures of considerable complexity at similar conditions were also swiftly borne out by experiment. It is remarkable that many of the elements hitherto regarded as 'simple' are observed to take up structures at higher densities even exhibiting incommensurabilities.
A major theme of the research is spurred by striking recent advances in experimental high pressure physics. The PI aims to elucidate the physics of the superconducting state, and particularly the role of electronic fluctuation in multi-band and quasi-localized contexts. High temperature superconductivity has long been predicted to occur in metallic phases of hydrogen and now more recently in hydrogen dominant metallic alloys. Further development of the theory for this class of system seems in order, especially to explore the possibility of further orderings that might accompany sublattice melting. For pure hydrogen itself, co-existence of superfluidity and superconductivity has been predicted for liquid metallic (near) ground states, and extension of the theory now to the mixed symmetry system embodied by liquid metallic deuterium is an interesting avenue to pursue, again with an eye towards experimental realization. In electronic terms all of these systems are highly inhomogeneous, as guaranteed by the cusp theorem, and this work will continue the development of weighted density and related approaches to the density functional viewpoint of the associated electronic structures, and could help illuminate the physics of transitions from the metallic state back to insulating or semiconducting.
NON-TECHNICAL SUMMARY: This award supports theoretical research and education in condensed matter physics focused mainly on the light elements, including hydrogen under extremes of pressure and temperature. A key feature of this work is the prediction of key signatures that could be observed in experiments. While hydrogen under enormous pressure exists in various places in our solar system and elsewhere in the universe, recent advances in experimental high pressure techniques suggest that the discovery of exciting new phases of matter with potential technological applications is coming within grasp. Among the possibilities are superconducting states that occur at high temperature in the light elements under high pressure. The PI will continue and extend his theoretical work to predict and explore new states of matter that may emerge in the seemingly simplest elements. Hydrogen and hydrogen-dominant metallic alloys under high pressure will be a particular focus of the work. This research may have impact on other disciplines and will provide a training ground for future scientists.
