Intrinsic Tunneling Spectroscopy for Pb-Substituted Bi2212 in the Underdoped Region

We measured intrinsic tunneling spectroscopy in mesa structures (S = 1 × 1μm2) of Bi1.9Pb0.1Sr2CaCu2O8+δ (PbBi2212) and Hall effect in PbBi2212 cleaved thin crystals. The doping level p of the PbBi2212 is estimated quantitatively through the comparison with LSCO, which is in the underdoped region. It is found that the Josephson critical current density Jc of PbBi2212 is less deviated from Ambegaokar Baratoff critical current density JcAB ≍ π Δ/2eRNS than the case of underdoped Bi2212. It is interpreted that the Pb substitution makes the tunnel barrier lower, resulting in a high superconducting pair density even with a lower doping.