Electron tunneling studies of Mo/sub 1-x/Re/sup x/: Enhancement of superconductivity by a resonance mode

Technical Report · Sat Nov 01 00:00:00 EST 1986

OSTI ID:7067990

Shum, D P.C.

It is well-known that a heavy impurity atom in a lattice of light atoms induces a lower frequency in-band resonance mode in the vibrational spectrum. The exact effect of such a mode on the lattice spectrum has not previously been reported and effects of such modes on superconductivity have not previously been described. Sputtered thin films of bcc Mo/sub 1-x/Re/sub x/, 0.2 < x < 0.4, have been prepared for this study because the Re atom is almost twice as heavy as Mo. High quality MoRe/Al/sub 2/O/sub 3//Pb tunnel junctions on these films have been made with an in situ deposited and subsequently oxidized thin Al layer as barrier. Three phonon peaks were observed directly in the dV/dI and d/sup 2/V/dI/sup 2/ curves. The ..cap alpha../sup 2/F(..omega..) spectra, determined from the data through the Eliashberg theory of superconductivity, all show an anomalous low energy peak, in addition to the Mo-derived transverse and longitudinal phonon peaks. This peak appears near 14 MeV, in agreement with the Brout-Visscher theory and with neutron scattering data which first indicated the Re resonance mode in Mo/sub .85/Re/sub .15/. We show that the resonance mode contributes strongly to ..cap alpha../sup 2/F(..omega..) and to strong coupling delta(=2..delta../k/sub B/T/sub c/ - 3.53) > 0. delta increases with lambda/sub R/, the Re contribution to the electron-phonon coupling constant lambda. The dependence of the anomalous softening and width of the resonance mode on lambda/sub R/ fit the Yu-Anderson theory of local phonon screening by a Fermi gas of electrons treated as Tomonaga bosons. These results explain the low N(0), high T/sub c/ behavior of Mo/sub .6/Re/sub .4/.

• Research Organization: Ames Lab., IA (USA)
• DOE Contract Number: W-7405-ENG-82
• OSTI ID: 7067990
• Report Number(s): IS-T-1246; ON: DE87003048
• Resource Relation: Other Information: Thesis
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
MOLYBDENUM ALLOYS
TUNNEL EFFECT
RHENIUM ALLOYS
PHONONS
QUANTITY RATIO
RESONANCE
SPUTTERING
SUPERCONDUCTING JUNCTIONS
SUPERCONDUCTIVITY
THIN FILMS
ALLOYS
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
FILMS
JUNCTIONS
PHYSICAL PROPERTIES
QUASI PARTICLES
360104* - Metals &amp; Alloys- Physical Properties
656100 - Condensed Matter Physics- Superconductivity