Emergence of superconducting gap features in Bi2Sr2CaCu2O8+delta single   crystals from intrinsic c-axis interlayer tunneling
  Static and dynamic transport measurements on stacks of intrinsic Josephson junctions on Bi2Sr2CaCu2O8+delta single crystals, near to optimal doping, are presented. The zero bias minimum in dynamic conductance is consistent with a normal state pseudo-gap. At Tc, a critical current develops simultaneously with new features consistent with a gap in the superconducting density states at an already well-established energy. The lack of thermal broadening and the small scale of the features force us to conclude a high degree of coherent interlayer tunneling in both the superconducting and normal states. 
I.F.G. Parker, M. Endres, P.J. Thomas, G. Yang, A. Yurgens, C.E. Gough