Superconducting critical current of a single Cu2O4-plane in   Bi2Sr2CaCu2O8+x single crystal
  By feeding current into the topmost $\mathrm{Cu_2O_4}$-layer of a mesa etched into the surface of a $\mathrm{Bi_2Sr_2CaCu_2O_{8+x}}$ (BSCCO) single crystal, we measured its superconducting critical value from a sharp upturn or break in current-voltage characteristics of the mesas. From this, we estimate the sheet critical current density of a single $\mathrm{Cu_2O_4}$ plane to be $\sim$\ 0.3-0.7 A/cm at 4.5 K, corresponding to the bulk current density of $2-5\ \mathrm{MA/cm^2}$. These values are among the largest ever measured for BSCCO single crystals, thin films and tapes. 
L. X. You, A. Yurgens, D. Winkler