Strong Shift of the Irreversibility Line in High-Tc Superconductors upon Vortex Shaking with an Oscillating Magnetic Field

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 Hc2(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.