Superconducting properties of ultrathin Bi2Sr2CaCu2O8+x single crystals
  We use Ar-ion milling to thin Bi2212 single crystals down to a few nanometers or one-to-two (CuO2)2 layers. With decreasing the thickness, superconducting transition temperature gradually decreases to zero and the in-plane resistivity increases to large values indicating the existence of a superconductor-insulator transition in ultrathin Bi2212 single crystals. 
L. X. You, A. Yurgens, and D. Winkler