The influence of low doses of columnar defects on the dissipation in layered high-T-c superconductors.

A number of workers have used columnar defects to increase flux pinning in the high T-c materials. However in single crystal whiskers of 2:2:1:2 BSCCO we find that a low concentration of 1.6 x 10(9) defects/cm(2) actually increases die dissipation in low magnetic fields. By 0.01T, H//c the excess dissipation disappears and at fields comparable to the matching field die dissipation is reduced. A dose of 4 x 10(9) defects/cm(2) is observed to have little effect on die dissipation in zero field, but by the matching field the dissipation is again reduced.