Superconducting properties of [BaCuOx]2/[CaCuO2]n artificial structures with ultrathick CaCuO2 blocks
Abstract
The electrical transport properties of [BaCuOx]2/[CaCuO2]n (CBCCO-2xn)underdoped high temperature superconducting superlattices grown by Pulsed Laser Deposition have been investigated. Starting from the optimally doped CBCCO-2x2 superlattice, having three CuO2 planes and Tc around 80 K, we have systematically increased the number n up to 15 moving toward the underdoped region and hence decreasing Tc. For n>11 the artificial structures are no longer superconducting, as expected, for a uniformly distributed charge carriers density inside the conducting block layer. The sheet resistance of such artificial structures (n nearly equal to 11) turns out to be quite temperature independent and close to the 2D quantum resistance 26 kOhm. A further increase of the number of CuO2 planes results in an 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 Superconducting and the Insulating regimes supports the fermionic scenario of the Superconductor-Insulator transition in these systems.
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