Vortex pinning in an irradiated Bi-2212 single crystal: What about the screening of the transverse magnetic field?

Abstract
Magneto-transport measurements I-V have been recorded for B=300G at both low and high temperature in Bi-2212 single crystals irradiated along the c-axis. Pinning properties have been studied versus the temperature T, and the angle between B and the columnar defects (CD's). We show that I _c decreases as t=T/T _c is lowered below 0.3. This result suggests that the rigidity of the moving vortex system increases as T decreases. The angular dependence of I _C confirms that, at low temperature, the pinning is collective as it has already been shown. More, the fact that the vortex penetration always take place parallel to the c-axis of the sample evidences an intrinsic infinite tilt modulus C44. At high temperature, C44 is finite and the localization of the discrete vortices takes place over different column sites. Key words. Columnar defects - Peak effect - Plasticity - Critical current - Decoupling.