Anomalous gap structures in HgBa₂Ca₂Cu₃O_8+γ single crystals measured by scanning tunneling spectroscopy

Scanning tunneling spectroscopy on high-Tc superconductors with nonideal surfaces can generate misleading results. We demonstrate that reproducible BCS-like gap structures with sharp peaks and very flat subgap conductance on HgBa2Ca2Cu3O8+δ (Hg-1223) single crystals (Tc, onset = 110 K) are in fact due to a combination of charging effects (Coulomb staircase) and superconductivity.