Direct observation of stress accumulation and relaxation in small   bundles of superconducting vortices in tungsten thin-films
  We study the behavior of bundles of superconducting vortices when increasing the magnetic field using scanning tunneling microscopy and spectroscopy (STM/S) at 100 mK. Pinning centers are given by features on the surface corrugation. We find strong net vortex motion in a bundle towards a well defined direction. We observe continuos changes of the vortex arrangements, and identify small displacements, which stress and deform the vortex bundle, separated by larger re-arrangements or avalanches, which release accumulated stress. 
I. Guillamon, H. Suderow, S. Vieira, J. Sese, R. Cordoba, J.M. De   Teresa and M.R. Ibarra
cond-mat.supr-con cond-mat.soft