Speaker
Beena Kalisky (Stanford U.)
(Stanford)
Description
We use scanning SQUID microscopy to investigate local
variations in the diamagnetic susceptibility in twinned
samples of two families of high temperature superconductors.
In Ba(Fe1-xCox)2As2 of the pnictides we observe increased
diamagnetic susceptibility on the twin boundaries in
underdoped, but not overdoped, single crystals. Vortex
behavior near the twin boundaries reveals that vortices
avoid pinning on the twins, and prefer to travel parallel to
them. These results indicate a relationship between
superfluid density, local strain, and frustrated magnetism,
and demonstrate two mechanisms for enhancing critical
currents. In YBa2Cu3O7-x of the cuprates vortices have been
observed to line up on the twin boundaries. I will show our
preliminary data on direct measurement of the susceptibility
near twin boundaries in YBa2Cu3O7-x . I will also show and
discuss SQUID imaging of vortices at very low fields in both
systems.