I. Low frequency noise in metal films at the superconducting transition. II. Resistance of superconductor - normal metal- superconductor sandwiches and the quasiparticle relaxation time

Technical Report · Fri Jul 01 04:00:00 EDT 1977

DOI:https://doi.org/10.2172/5047982· OSTI ID:5047982

Hsiang, T Y

Measurements of the noise power spectra of tin and lead films at the superconducting transition in the frequency range of 0.1 Hz to 5k Hz are reported. Two types of samples were made. Type A were evaporated directly onto glass substrate, while Type B were evaporated onto glass or sapphire substrate with a 50A aluminum underlay. The results were consistent with a thermal diffusion model which attributes the noise to the intrinsic temperature fluctuation in the metal film driven with a random energy flux source. In both types of metal films, the noise power was found to be proportional to (V-bar)/sup 2/ ..beta../sup 2//..cap omega.., where V-bar was the mean voltage across the sample, ..beta.. was the temperature coefficient of resistance and ..cap omega.. was the volume of the sample. Correlation of noises in two regions of the metal film a distance d apart was detected at frequencies less than or = D/..pi..d/sup 2/. A possible explanation of the noises using quantitative boundary conditions and implications of this work for device applications are discussed. Theoretical and experimental investigation are reported on the resistance of superconductor-normal metal-superconductor sandwiches near T/sub c/. The increase in SNS resistance is attributed to the penetration of normal electric current in the superconductor. It is proved from first principles that an electric field can exist inside the superconductor when quasiparticles are not equally populated on the two branches of the excitation spectrum, and such is the case in a current biased SNS junction. The electric field inside S decays according to a diffusion law. The diffusion length is determined by the quasiparticle ''branch-crossing'' relaxation time. The branch-crossing relaxation times were measured. Impurity-doping of tin was found to decrease this relaxation time.

• Research Organization: California Univ., Berkeley (USA). Lawrence Berkeley Lab.
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 5047982
• Report Number(s): LBL-6611
• 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
DIFFUSION
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
ELEMENTS
FILMS
IMPURITIES
LEAD
METALS
NOISE
PHYSICAL PROPERTIES
QUASI PARTICLES
RELAXATION
SUPERCONDUCTING FILMS
SUPERCONDUCTING JUNCTIONS
SUPERCONDUCTIVITY
THERMAL BOUNDARY RESISTANCE
TIN