Hole redistribution across interfaces in superconducting cuprates superlattices

With the aim of disentangling the role of the constituent blocks in the high-${T}_{c}$ cuprate superconductors we have measured x-ray absorption spectra at the $\text{Cu}\text{ }{L}_{3}$ edge on $({\text{Cu}}_{1\ensuremath{-}\ensuremath{\delta}}{\text{C}}_{\ensuremath{\delta}}){\text{Ba}}_{2}\phantom{\rule{0.1em}{0ex}}\text{Cu}{\text{O}}_{x}$ (BCO), ${\text{CaCuO}}_{2}$ (CCO), and BCO/CCO superconducting superlattices obtained by stacking in a sequence the two blocks. By observing the polarization dependence we could discriminate between the in-plane and out-of-plane hole densities. The results strongly indicate that charge is redistributed across the interfaces from the BCO charge reservoir block to the CCO infinite layer block. In the superconducting samples a relatively high density of out-of-plane holes is still present, whereas when the CCO layer thickness is excessive the holes appear to have preferential in-plane orientation and superconductivity is suppressed.