CAREER: Theory and Modelling of Non-Uniform Superconductors and Superfluids

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TECHNICAL SUMMARYThis CAREER award supports theoretical and computational research and education to investigate non-uniform superconducting states and their origin in novel superconductors and superfluid helium-3. Inhomogeneous states appear due to a complex interplay of multiple energy scales that lead to strong local modification of the quasiparticle spectrum and, macroscopically, to states with new symmetries. Such states are expected to play major roles in strongly correlated materials, systems with competing orders, and in the interface regions of small-scale devices.The search for superconductors with higher critical temperature and better material characteristics has led to the discovery of new families of complex materials with exotic properties. Besides superconductivity, most display some kind of magnetic order which may significantly influence superconducting properties, and may provide or contribute to the pairing interaction that leads to superconductivity. Similar behavior may have also been observed in spin-triplet superfluid helium-3 in confined geometries. Experiments suggest many new condensate phases that are thought to be non-uniform.This research will focus on presenting a comprehensive picture of non-uniform states in heavy fermion materials, superconductors without inversion center, FeAs-pnictides, and superfluid helium-3 films. New states and their thermodynamic, transport and magnetic properties will be studied in these systems, including strong-coupling and non-equilibrium phenomena. This project will advance understanding of the nature of new superconducting states of matter and help to link theory and experiment. The theoretical and numerical approach will be based on a quasiclassical formulation of the theory of superconductivity that will include magnetic degrees of freedom, multiple bands, and significant spin effects. The results of this research may contribute to the realization of superconductor-based devices with superconducting interfaces. The study of magnetically active superconducting surfaces may influence appearance of new charge- and spin-coupled electronics. The research inspires demonstrations of the most influential principles of physics, such as symmetry and emerging complexity in many-particle systems. This forms the basis of the education component which involves the development of new courses on both graduate and undergraduate levels, and the development of an educational website with graphical demonstrations and links to other physics, chemistry and biological research conducted at Montana State University.NONTECHNICAL SUMMARYThis CAREER award supports theoretical and computational research and education to investigate the nature of superconductivity in materials, that are highly non-uniform, have special arrangements of atoms, or display an interplay between magnetism and superconductivity. Superconductivity is an extraordinary state of electrons that can occur in some materials at sufficiently low temperatures. Unlike common wires made of, for example, copper, a superconductor can carry electric current without dissipation. Superconductors have other unusual properties that make them promising for applications in future electronic device technologies. This research will explore materials and conductions under which superconductivity can vary or can change from one superconducting state to another in the same material, for example in response to regions of magnetic order. This research may predict new phenomena in superconductors and in superfluids. Superfluids generalize the concept of superconductivity beyond electrons in a material to liquid states, for example those that that occur in liquid helium at temperatures approaching absolute zero. Superconductivity and more generally superfluidity is an intriguing state of matter that requires a quantum mechanical description and remains fertile not only intellectually in the discovery of new superconducting states and phenomena, but also for its potential applications, for example in new electronic devices and power transmission. This research inspires demonstrations of some of the most powerful principles of condensed matter physics, such as symmetry and emerging complexity in many-particle systems. It also forms the basis of the education component which involves the development of new courses at both graduate and undergraduate levels, and the development of an educational website with graphical demonstrations and links to other physics, chemistry and biological research conducted at Montana State University.