Universal features of tunneling conductance on high-Tc cuprates

We present tunneling spectra measured at 4.2 K on several high- T c cuprates including Bi 2+ y Sr 2−( x + y ) La x CuO 6+ δ (Bi2201), Tl 2 Ba 2 CuO y , Bi 2 Sr 2 CaCu 2 O 8+ δ (Bi2212) single crystals, as well as (Cu,C)Ba 2 Cu 3 Cu 4 O 12+ δ polycrystals, using SIN point contact method. All of high quality tunneling conductances on these samples exhibit not only a well-defined superconducting gap peak at Δ but also the high energy features known as dip (hump) at roughly ∼2 Δ (∼3 Δ ). In addition, it is demonstrated that analogous to Bi2212, the superconducting gap in Bi2201 monotonically increases with decreasing hole concentration. It is concluded that the dip and hump features as well as the doping dependence of energy gap are generic to high temperature superconductors.