Tcup to 50 K in superlattices of insulating oxides

Here we report a structural and electronic investigation of the recently discovered CaCuO 2 /SrTiO 3 superconducting artificial superlattices based on two insulating oxides. We show that T c = 50 K is reached in the superlattices grown on NdGaO 3 substrate under optimized growth conditions. If the superlattices are grown on LaAlO 3 substrate the T c is drastically reduced due to the much higher lattice mismatch between CaCuO 2 and LaAlO 3 , which has lattice parameters substantially smaller than NdGaO 3 . The consequent in-plane lattice contraction also makes the incorporation of extra oxygen atoms more difficult, leading to a decrease of hole doping and T c . Finally, x-ray absorption spectroscopy study as a function of the thickness of the CaCuO 2 block in CaCuO 2 /SrTiO 3 superconducting superlattices has revealed the important role played by the interfaces as the location of hole doping and superconductivity in these systems.