Is there an intrinsic difference between bulk YBCO and a single unit-cell layer?

The reduction of Tc in ultrathin films of YBCO in multilayers has often been assumed to be the result of the absence of essential transverse coupling. Our work shows instead that the changes in Tc are correlated with changes in conductance, which are the result of extrinsic effects, such as charge transfer and defects at the interfaces. Except for these effects there seems to be no evidence for any change in the YBCO properties down to the thickness of a single unit-cell layer.