Superconducting energy gap in Bi[sub 1. 8]Pb[sub 0. 4]Sr[sub 2]Ca[sub 2]Cu[sub 3]O[sub 10+[delta]] studied by photoemission spectroscopy

We report photoemission measurements on highly textured polycrystalline samples of Bi[sub 1.8]Pb[sub 0.4]Sr[sub 2]Ca[sub 2]Cu[sub 3]O[sub 10+[delta]] (Bi-2223, [ital T][sub [ital c]]=104 K). High-resolution data show a superconducting gap opening below [ital T][sub [ital c]]. The gap-spectrum line shape suggests an anisotropic gap structure in the Brillouin zone. The maximum gap in Bi-2223 is estimated to be 29 meV so that 2[Delta]/[ital kT][sub [ital c]][similar to]6.5, somewhat larger than the reduced gap in Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub 8] (Bi-2212). A spectral dip feature is observed at 72 meV in the superconducting state. The results are compared with angle-resolved experiments on Bi-2212 single crystals.