Suppression of the superconducting energy gap in intrinsic Josephson   junctions of $\mathbf{Bi_2Sr_2CaCu_2O_{8+\delta}}$ single crystals
  We have observed back-bending structures at high bias current in the current-voltage curves of intrinsic Josephson junctions. These structures may be caused by nonequilibrium quasiparticle injection and/or Joule heating. The energy gap suppression varies considerably with temperature. Different levels of the suppression are observed when the same level of current passes through top electrodes of different sizes. Another effect which is seen and discussed, is a super-current ``reentrance'' of a single intrinsic Josephson junction with high bias current. 
L. X. You, P. H. Wu, J. Chen, W. W. Xu, K. Kajiki, S. Watauchi and I.   Tanaka