Evidence for two energy scales in the superconducting state of optimally doped (Bi,Pb)2(Sr,La)2CuO6+δ

We use angle-resolved photoemission spectroscopy to investigate the energy gap(s) in (Bi,Pb)(2)(Sr,La)(2)CuO6+delta. We find that the spectral gap has two components in the superconducting state: a superconducting gap and pseudogap. Differences in their momentum and temperature dependence suggest that they represent two separate energy scales. Spectra near the node reveal a sharp peak with a small gap below T-c that closes at T-c. Near the antinode, spectra are broad with a large energy gap of similar to 40 meV above and below T-c. The latter spectral shape and gap magnitude are almost constant across T-c, indicating that the pseudogap state coexists with the superconducting state below T-c, and it dominates spectra around the antinode. We speculate that the pseudogap state competes with the superconductivity by diminishing spectral weight in antinodal regions, where the superconducting gap is largest.