This individual investigator award supports a project addressing the fundamental issues concerning the vortex state of type-II superconductors. Type-II superconductors are of broad scientific and technological importance, and their physical properties are controlled by the basic physics of the vortex state. Recent neutron scattering experiments on weak-pinning crystalline Nb have led to the discovery of a Bragg-glass melting (disordering) transition at the well-known peak-effect anomaly, and a multicritical point on the Bragg-glass phase boundary, suggesting that the formation of the Bragg glass phase can be either a mean-field transition directly from the normal state as predicted by Abrikosov, or a first-order freezing transition from a disordered vortex liquid (or glass) as envisioned by the Bragg glass theory. The proposed program is to use small angle neutron scattering and other complementary techniques to test whether the new vortex phase diagram discovered in Nb is applicable to other important type-II superconductors, and whether the peak effect is related to other types of phase transitions in vortex matter. The proposed work will lead to new insights into the fundamental properties of type-II superconductors, and a firm understanding of the phases and phase transitions in condensed matter systems with random pinning. The graduate and undergraduate students will learn state-of-the-art neutron scattering techniques, acquire a wide range of materials research experiences in thermodynamic and ultrasonic measurements, and participate in the frontier research of superconductivity. Thus, they will be prepared for future careers in academia, industry, or government.
Type-II superconductors are those that, under certain temperature and magnetic field conditions, have a mixed state. The mixed state consists of superconducting regions as well as non-superconducting regions containing a magnetic field. These latter regions are known as vortices. Type-II superconductors are of broad scientific and technological importance, and their physical properties are controlled by the basic physics of the vortex state. This individual investigator award supports a project addressing the fundamental issues of the vortex state. Recent neutron scattering experiments on the well-known type-II material niobium led to the discovery of a melting-type phase transition in the vortex state. This led to a newly discovered phase diagram, or behavior of the vortex state when then the temperature and/or the magnetic field are varied. The project will use small angle neutron scattering and other complementary techniques to test whether the vortex phase diagram in niobium is applicable to other important type-II superconductors. The proposed work will lead to new insights into the fundamental properties of type-II superconductors, and a firm understanding of the phases and phase transitions in superconducting materials. The graduate and undergraduate students will learn state-of-the-art neutron scattering techniques, acquire a wide range of materials research experiences in thermodynamic and ultrasonic measurements, and participate in the frontier research of superconductivity. Thus, they will be prepared for future careers in academia, industry, or government.
