Tunneling STM/STS and break-junction spectroscopy of the Pb-doped Bi2223 superconductor

Abstract

The combined scanning tunneling microscopy/spectroscopy (STM/STS) and the break-junction tunneling spectroscopy (BJTS) measurements of the three-layered Pb _x Bi_2-x Sr₂Ca₂Cu₃O_10+y cuprate superconductors were carried out. The averaged dI/dV spectrum obtained by the STS shows the gap Δ _STS ≈ 45 meV, while that of BJTS shows Δ _BJ ≈ 35 meV. In case of the BJTS measurements, we also referred the zero bias (ZB) peak as being due to the maximum Josephson current I_Jc . The product of I_Jc and normal resistance R_N (I_JcR_N ) was obtained I_JcR_N ≈ 3.5 mV at T = 11 K, which is one order lower than that of the BCS-based Ambegaokar-Baratoff theory with Δ _BJ =35 meV taken into account. With increasing the temperature, the I_JcR_N was reduced and vanished just below the T_c (≈ 106 K), indicating the bulk superconductivity. Simultaneously, from the temperature dependence of the gap features from 80 K to 120 K, the gap Δ was shown to persist across the T_c , indicating that the I_JcR_N product is a significant parameter for understanding the cuprate superconductivity.