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Physics and Astronomy

Physics & Astronomy Colloquium

3:30 PM, Friday, September 3, 2010
Room 155, Chem-Phys Building

Dr. Sean Ling
Department of Physics
Brown University

Neutron Scattering Studies of Vortex Matter in Type-II Superconductors: Search for Bragg Glass
Ever since the famous "Imry-Ma theorem" of 1975, it was widely accepted in condensed matter physics that true phase transition cannot occur in any real system with an order parameter from a broken-continuous symmetry, e.g. crystallization. This is because real systems contain "quenched disorder", random static impurities, which tend to prevent true long-range order even in cleanest samples with weak random pinning. A classical example is the vortex lattice in type-II superconductors. Random pinning gives the useful property of supercurrent which makes superconducting magnets possible. An unresolved question is whether the vortex matter in weak-pinning systems (such as Nb and YBCO single crystals) can form an ordered solid at low-temperatures. In this talk, I'll discuss our latest neutron scattering data which will clarify a number of issues in vortex physics, such as why some samples exhibit disordered vortex state in zero-field-cooling path. With proper thermal annealing, a Bragg glass phase can be found in all Nb crystals, thus establishing the universality of the Bragg glass concept.

Refreshments will be served in CP 179 at 3:15 PM