Physics & Astronomy Colloquium
3:30 PM, Friday, September 3, 2010
Room 155, Chem-Phys Building
Dr. Sean Ling
Department of Physics
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