Multilayer effects in Bi2Sr2Ca2Cu3O10+z superconductors

We discuss the characteristic features of triple CuO2 layer cuprate superconductors through comparisons with single and double layer ones. After a brief introduction to multilayer cuprates and their characteristic properties, such as the doping imbalance between the inner and outer CuO2 planes (IP and OP, respectively) revealed by nuclear magnetic resonance, we present the experimental results of angle-resolved photoemission and Raman scattering spectroscopy for the triple layer Bi2Sr2Ca2Cu3O10+z. These showed two different superconducting gaps opening on the IP and OP. The doping dependence of the double peak structure in the Raman spectra was found to be qualitatively consistent with that of single and double layer cuprates, if each layer doping for the IP and OP is taken into account. The fact that the IP and OP share the same electronic phase diagram and transition temperature (T-c) hints at a coupling between the IP and OP. Moreover, the energies of IP and OP Raman peaks were found to be very large and not scaling with T-c, which can be attributed to the strong influence of the pseudogap of the underdoped IP in triple layer cuprates. These findings suggest that the high T-c and the large gap ratio of triple layer cuprates are realized through a combination of the interlayer coupling between the OP and IP and the interaction between superconductivity and the pseudogap.