University
of Toronto
Physics Department
Quantum Optics and Condensed Matter
SPECIAL SEMINAR
Please note unusual date and time
University
of Toronto
SPECIAL SEMINAR
Please note unusual date and time
| Speaker : | Britton Plourde
Department of Physics University of Illinois at Urbana-Champaign |
| Topic : | Vortex dynamics in superconducting systems
imaged by Scanning SQUID Microscopy |
| Time : | Friday, April 7 at 1:00 p.m. |
| Place : | Room 408, Burton Tower 60 St. George Street / 255 Huron Street |
Abstract
Using a Scanning SQUID Microscope (SSM), we have studied vortex distributions
in various superconducting systems. The excellent flux sensitivity
of the SSM allows us to resolve individual vortices for low flux density.
Field cooling produces quenched vortex patterns which can be disordered
in strong-pinning Nb films or well ordered into a lattice in a-MoGe films
with weak pinning. Surface steps alter the field-cooled patterns,
with vortices formed in dense rows along the low side of steps with few
vortices near the high side. We observe an asymmetry in the dynamics
of vortices around the surface steps under the application of a driving
force. The vortex line tension impedes vortex motion from thin parts
of the superconductor to thick regions, while not affecting the opposite
motion down the steps. We have also investigated the behavior of
vortices in thin superconducting strips in a perpendicular magnetic field,
a complex problem due to the large demagnetizing effects. These geometrical
barriers are frequently encountered in transport measurements on high-Tc
superconductors. Strips with transverse surface steps as well as
strips with a uniform cross section have been imaged. We are attempting
to correlate the observed vortex distributions with transport measurements
of the vortex dynamics in the strips.
Local Host: Prof
John Wei 
416-978-5943