Proceedings Article | 1 March 1991
Douglas Lowndes, David Norton, J. Budai, D. Christen, C. Klabunde, R. Warmack, Stephen Pennycook
KEYWORDS: Superlattices, Superconductors, Technetium, Electrons, Modulation, Transistors, Oxygen, Anisotropy, Transmission electron microscopy, Deposition processes
The pulsed-laser deposition method has been used to fabricate epitaxial, nonsymmetric M(Y) x N(Pr)
superlattices in which YBa2Cu3O7 (YBCO) layers either M = 1, 2, 3, 4, 8, or 16 c-axis unit cells thick are
separated by insulating PrBa2Cu3O7 (PBCO) layers N unit cells thick (N = I to -32). The zero-resistance
superconducting transition temperature, Tc0, initially decreases rapidly with increasing PBCO layer thickness,
but then saturates at TcO 19 K, 54 K, 71 K, or 80 K, for structures containing 1-, 2-, 3-, or 4-cell-thick YBCO
layers, respectively. Critical current density measurements carried out on structures with 16- or 32-cell thick
YBCO layers show that the magnitude of Jc(H 0) 12 MA/cm2, as well as the magnetic field dependence and
the anisotropy of Jc(H) all are in good agreement with corresponding measurements on thicker, single-layer
YBCO films. Thus, there is no evidence of an enhanced Jc(H) due to the multi-layered structure, for the layer
thicknesses investigated to date. The systematic variation of Tc0, as a function of the YBCO and PBCO layer
thicknesses, is discussed in light of other recent experiments and theoretical model calculations. The
superlattices' structural and compositional order are characterized using x-ray diffraction, transmission
electron microscopy, and scanning tunneling microscopy, and details of the pulsed-laser deposition process are
reported.
