The AC magnetic penetration depth λ(T,H,j) was measured in presence of a macroscopic DC (Bean) supercurrent, j. In single crystal BSCCO below approximately 28 K, λ(T,H,j) exhibits thermal hysteresis. The irreversibility arises from a shift of the vortex position within its pinning well as j changes. It is demonstrated that below a new irreversibility temperature, the nonequilibrium Campbell length depends upon the ratio j/jc. λ(T,H,j) {\it increases} with j/jc as expected for a non-parabolic potential well whose curvature {\it decreases} with the displacement. Qualitatively similar results are observed in other high-Tc and conventional superconductors.
Cite
@article{arxiv.cond-mat/0004122,
title = {Nonequilibrium Campbell length: probing the vortex pinning potential},
author = {R. Prozorov and R. W. Giannetta and T. Tamegai and P. Guptasarma and D. G. Hinks},
journal= {arXiv preprint arXiv:cond-mat/0004122},
year = {2007}
}