Intrinsic tunneling spectroscopy for Bi2−xPbxSr2CaCu2O8+δ of nm-thickness mesa structure

► Intrinsic tunneling spectroscopy is investigated in PbBi2212. ► The value of the superconducting gap corresponds to one in the underdoped Pb-free Bi2212. ► Pb substitution makes the tunnel barrier lower, resulting in low anisotropy. ► Josephson critical current density increases with decreasing anisotropy even in the underdoped region.