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

We use angle-resolved photoemission spectroscopy (ARPES) to investigate the properties of the energy gap(s) in optimally doped (Bi,Pb)2(Sr,La)2CuO6+d (Bi2201). We find that the spectral gap has two components in the superconducting state: a superconducting gap and pseudogap. Significant 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 Tc that closes at Tc. Near the antinode, the spectra are broad with a large energy gap of ~40meV above and below Tc. The spectral shape and gap magnitude around the antinode are almost constant across Tc, which indicates that the pseudogap state coexists with the superconducting state below Tc, and it dominates the character of the spectra around the antinode. We speculate that the pseudogap state competes with the superconductivity by diminishing spectral weight in the antinodal regions, where the magnitude of the superconducting gap is largest.