Interlayer tunneling spectroscopy and doping-dependent energy-gap structure of the trilayer superconductorBi2Sr2Ca2Cu3O10+δ

Abstract

The superconducting gap, the pseudogap, and their doping and temperature dependences have been measured by the short-pulse interlayer tunneling spectroscopy for the ${\mathrm{CuO}}_{2}$ triple-layer $\mathrm{h}\mathrm{i}\mathrm{g}\mathrm{h}\ensuremath{-}{T}_{\mathrm{c}}$ superconducting ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{Ca}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{10+\ensuremath{\delta}}$ system. It is found for a nearly optimally doped sample that the superconducting gap magnitude is $\ensuremath{\approx}80\mathrm{meV}$ and the pseudogap is \ensuremath{\approx}120 meV, the values of which are slightly larger than those for ${\mathrm{CuO}}_{2}$ double-layer system. Both gap magnitudes show a clear tendency to decrease with increasing doping. In an underdoped sample, a clear dip-and-hump structure is observed, which declines with increasing doping and tends to diminish in overdoped samples. The relationship between unchanged ${T}_{\mathrm{c}}$ and decreasing superconducting gap in the overdoped region is discussed in terms of the proximity effect applied to the inequivalent doping model. We also discuss the dip-and-hump structure in comparison with other spectroscopic results. Finally, we argue an important implication of the increasing maximum Josephson current and the decreasing superconducting gap magnitude, both with increasing doping.