Predominantly Superconducting Origin of Large Energy Gaps in Underdoped   Bi2Sr2CaCu2O8-d from Tunneling Spectroscopy
  New tunneling data are reported in underdoped Bi2Sr2CaCu2O8-d using superconductor-insulator-superconductor break junctions. Energy gaps, Delta, of 51+2, 54+2 and 57+3 meV are observed for three crystals with Tc=77, 74, and 70 K respectively. These energy gaps are nearly three times larger than for overdoped crystals with similar Tc. Detailed examination of tunneling spectra over a wide doping range from underdoped to overdoped, including the Josephson IcRn product, indicate that these energy gaps are predominantly of superconducting origin. 
N. Miyakawa, J. F. Zasadzinski, L. Ozyuzer, P. Guptasarma, D. G.   Hinks, C. Kendziora and K.E. Gray