Superconducting gap and pseudogap in Bi₂Sr₂Ca₂Cu₃O _10+δ by short-pulse interlayer tunneling spectroscopy

We have measured the superconducting gap, pseudogap and their doping dependence of CuO₂ trilayer high-T_c superconductor Bi₂Sr₂Ca₂Cu₃O_10+δ by short-pulse interlayer tunneling spectroscopy. While both gaps exhibit temperature dependence similar to those for the bilayer system, their doping dependence behaves differently from that of T_c, presenting an anomalous relationship between T_c and the gap magnitude. In the overdoped region, T_c remains almost unchanged from its optimum value irrespective of doping, while the gap decreases with increasing doping. This is suggestive of inequivalent hole doping in the inner and outer planes, which is thought to occur in trilayer systems.