Dependence of the critical temperature on n in (BaCuO2)2/(CaCuO2)n superlattices

(BaCuO2)(2)/(CaCuO2)(n) superconducting superlattices have been grown by pulsed laser deposition for n ranging from 1 to 6. The critical temperature was found to depend strongly on the growth conditions. A maximum T-c value of about 80 K (zero resistance temperature) was found for superlattices grown at high oxygen pressure (P-O2 similar or equal to 0.8 mbar) and relatively high temperature (T-g similar or equal to 600 degrees C). The dependence of T-c on the number n of CaCuO2 layers (for superlattices grown exactly in the same conditions) was investigated. T-c versus n showed the expected behavior with a maximum T-c value of 80 K for n = 2-3. However, such value is somewhat lower than that expected for a cuprate structure containing 3-4 CuO2 planes and having an optimum carrier concentration. Two possible explanations for this effect can be envisaged. The first one deals with the chemistry of the "charge reservoir" block, the second one with the special role of interelectron interaction in these highly disordered artificial structures. Finally, it is shown that, taking into account the degree of disorder, a shift of T-c of about 20 K relative to the bulk value T-c0, consistent with the microscopic parameters of these materials, can be foreseen. [S0163-1829(98)51334-3].