Structure and superconductivity of Nb/Pd(Mn) multilayers

J.M. Slaughter, James Eickmann, U. Hiller, Satoru Kaneko* and Charles M. Falco

Optical Sciences Center and Department of Physics
The University of Arizona, Tucson, Arizona  85721

C. Coccorese, C. Attanasio, L. Maritato and M. Salvato

Dipartimento di Fisica, Universita' di Salerno, 84081 Baronissi, Italy

We have grown Nb/Pd multilayers by sputtering and Nb(110)/Pd(111)
superlattices by molecular beam epitaxy(MBE).  Low-angle x-ray reflectance and
high-angle x-ray diffraction at =1.54 � were used to characterize their
structure.  In addition to the ex situ x-ray characterization, the MBE-grown
samples were characterized in situ by reflection high energy electron
diffraction.  Measurements of their superconducting critical temperature (TC)
as a function of Pd layer thickness were used to study their superconducting
behavior.  The MBE samples were grown on Cu(111) buffer layers which were
grown on Si(111) wafers.  Thick films of pure Nb and Pd were used to measure
the electron mean free paths and the TC of the pure Nb.  Although the
structure of the sputter-deposited multilayers is good, the superconducting
properties are strongly affected by residual contamination.  In contrast, the
MBE-grown films exhibit high residual resistivity ratios and TC of the thick
Nb film is not depressed from the bulk value as it is in the polycrystalline
sputter-deposited films.  The behavior of TC as a function of Pd layer
thickness is in agreement with the deGennes-Werthamer proximity effect theory,
showing that Nb/Pd is a conventional proximity system.

This work was supported by the Office of Naval Research under contract
N00014-92-J-1159.

* Permanent address:  Industrial Research Institute of Kanagawa
Prefecture, 3173 Showa-machi, Kanazawa-ku, Yokahama 236, Japan.