Z-contrast electron microscopy demonstrates that interdiffusion is not affecting the resistive transitions observed in M×N ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}2}$/${\mathrm{PrBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathit{x}}$ superlattices. At moderate supersaturations, island growth is observed, the islands comprising one Ba-Y-Ba structural unit in height terminated at the Cu-chain plane, having sides 20–30 nm long along [100] and [010]. The associated gradual roughening of the growing surface has no apprent effect on critical currents for M≥2, the temperature and field dependence being comparable to that of a film.

• Received 4 April 1991

DOI:https://doi.org/10.1103/PhysRevLett.67.765