Orderings in Highly Quantal Light Element Systems

Cornell University, Ithaca NY

Investigators

Abstract

TECHNICAL SUMMARY: This award supports theoretical research and education focused mainly on the light elements, including hydrogen under conditions of high pressure and eventually 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 compressed lithium with a transition temperature which is now the highest of any element. 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. And it is surely also noteworthy that the light elements in the especial combination MgB2 have had such a significant impact on the field of superconductivity. 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. The vortex characteristics, resulting either from applied magnetic fields or from rotation, may be unusual. In electronic terms all of these systems are highly inhomogeneous, as guaranteed by the cusp theorem, and it is also proposed to further develop weighted density and related approaches to the density functional viewpoint of the associated electronic structures, both for energetics and for effective interactions. NON-TECHNICAL SUMMARY: This award supports theoretical research and education in condensed matter physics focused mainly on the light elements, including hydrogen under extermes of pressure and temperature. Under a previous award the PI has predicted that novel superconducting and superfluid states in these systems will arise when exposed to a magnetic field or when they are rotated. 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 simplist 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.