Superconducting properties of [BaCuOx](2)/[CaCuO2](n) artificial structures with ultrathick CaCuO2 blocks

The electrical transport properties of [BaCuOx](2) /[CaCuO2](n)(CBCCO-2 X n ) underdoped high-temperature superconducting superlattices grown by pulsed laser deposition have been investigated. Starting from the optimally doped CBCCO-2 X 2 superlattice, having three CuO2 planes and T-c around 80 K, we have systematically increased the number n up to 15 moving toward the unde rdoped region and hence decreasing T-c. For n > 11 the artificial structure s are no longer superconducting, as expected, for a uniformly distributed c harge carrier density inside the conducting block layer. The sheet resistan ce of such artificial structures (n approximate to 11) turns out to be quit e temperature independent and close to the two-dimensional quantum resistan ce 26 k Omega. A further increase of the number of CuO2 planes results in a n insulator-type dependence of R(T) in the wide range of temperatures from room temperature to 1 K. The value of the sheet resistance separating the s uperconducting and the insulating regimes supports the fermionic scenario o f the superconductor-insulator transition in these systems.