Strong shift of the irreversibility line in high-Tcsuperconductors upon vortex shaking with an oscillating magnetic field

Abstract

Torque magnetometry is a powerful method for probing superconducting anisotropy in the mixed state. In order to use the three-dimensional anisotropic London model to analyze torque data, the vortex lattice must be in a reversible state, a state normally restricted to a narrow range close to the upper critical-field boundary ${H}_{c2}(T)$ because of large pinning effects that set in at lower temperatures $T.$ We show that the application of an additional oscillating magnetic field perpendicular to the main field $B$ leads to a fast depinning of the vortex lattice. This vortex-shaking process dramatically extends the reversible domain in the $(H,T)$ phase diagram, and thus the range in which torque investigations can be made.