LAUSR

Abstract The heavily underdoped (Bi,Pb) 2 Sr 2 (Ca,Y)Cu 2 O 8+δ single crystals were successfully grown by conventional floating zone technique with a very slow growth rate of 0.20 mm/h. The superconducting gap of prepared single crystals was investigated by means of laser induced ARPES measurement. We found that the superconducting gap was kept almost unchanged from optimally doped region, T c  = 92 K, to heavily underdoped region, T c  ∼ 12 K. The result suggest that the pair-formation-energy in underdoped region is similar to that in optimally doped region, and the superconducting temperature is presumably suppressed by the pseudogap which increase with decreasing hole concentration.