Analysis of the charge transfer mechanism on ( Ba 1 − x Nd x CuO 2 + δ ) 2 / ( CaCuO 2 ) n superconducting superlattices by thermoelectric power measurements

We have investigated the charge transfer mechanism in artificial superlattices by Seebeck effect measurements. Such a technique allows a precise determination of the amount of charge transferred on each ${\mathrm{CuO}}_{2}$ plane. A systematic characterization of thermoelectric power in $({\mathrm{BaCuO}}_{2+\ensuremath{\delta}}{)}_{2}/({\mathrm{CaCuO}}_{2}{)}_{n}$ and $({\mathrm{Ba}}_{0.9}{\mathrm{Nd}}_{0.1}{\mathrm{CuO}}_{2+\ensuremath{\delta}}{)}_{2}/({\mathrm{CaCuO}}_{2}{)}_{n}$ superlattices demonstrates that electrical charge distributes uniformly among the ${\mathrm{CuO}}_{2}$ planes in the Ca block. The differences observed in the Seebeck effect behavior between the Nd-doped and undoped superlattices are ascribed to the different metallic character of the Ba block in the two cases. Finally, the special role of structural disorder in superlattices with $n=1$ is pointed out by such analysis.