A15 niobium-tin: fabrication and superconductive tunneling spectroscopy

Thesis/Dissertation · Sat Jan 01 04:00:00 EST 1983

OSTI ID:6848573

Rudman, D A

The material and superconducting properties of A15 phase niobium-tin have been studied by tunneling spectroscopy. The ability to fabricate high-quality tunnel junctions on transition-metal compounds has been made possible by the combined use of thin-film deposition techniques and an artificial tunneling barrier. The material is synthesized by co-deposition of niobium and tin in an electron-beam evaporator. Careful control of the substrate temperature during deposition has proved critical to improving the homogeneity and reproducibility of the films. The tunneling barrier is formed from a thin (2-3 nm) layer of amorphous silicon, deposited in vacuum on the freshly-made base electrode, and then oxidized in air. This barrier has proved generally applicable to a wide variety of materials. The tunnel junctions formed on these films are of high quality, but exhibit some non-ideal behavior independent of the deposition techniques used. Most notably, the measured tunneling density of states at the superconducting gap edge is much broader than for a BCS superconductor, suggesting a distribution of gap values at the surface of the material. In addition, off-stoichiometry samples (tin poor) deposited at substrate temperatures below 800/sup 0/C have gap values (determined by tunneling) that are too small for the inductively measured critical temperature. This produces calculated values of the coupling strength below the BCS weak-coupling limit. It has been found that increasing the deposition temperature above 850/sup 0/C eliminates this problem. The tunneling density of states can be used with the proximity-effect modified Eliashberg equations to calculate the electron-phonon coupling spectrum.

• Research Organization: Stanford Univ., CA (USA)
• OSTI ID: 6848573
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360104* -- Metals & Alloys-- Physical Properties
656102 -- Solid State Physics-- Superconductivity-- Acoustic
Electronic
Magnetic
Optical
& Thermal Phenomena-- (-1987)
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ALLOYS
DATA
ELECTRON-PHONON COUPLING
ENERGY GAP
ENERGY-LEVEL DENSITY
EXPERIMENTAL DATA
FABRICATION
FILMS
INFORMATION
JUNCTIONS
NIOBIUM ALLOYS
NUMERICAL DATA
SPECTROSCOPY
SUPERCONDUCTING FILMS
SUPERCONDUCTING JUNCTIONS
TEMPERATURE DEPENDENCE
TIN ALLOYS
TUNNEL EFFECT