The onset of superconductivity in two-dimensional disordered systems
Investigations of ultra-thin films grown by quench-evaporation and studied in-situ show an interesting evolution of normal and superconducting properties as the films are made thinner. The films are categorized into two different classes based on the nature of the evolution of superconductivity in each class: granular and homogeneous. Granular films show rich behavior which is believed to be due to quantum fluctuations of the phase of the superconducting order parameter. The onset of quasi-reentrant behavior is correlated with the activation energy of normal state conduction becoming the order of the superconducting gap, where the normal state conduction is modeled by a hopping conduction mechanism in the presence of strong Coulomb interactions. This Josephson coupling of superconducting grains on a local scale gives way to global superconducting coupling as the film is made thicker and less resistive. Homogeneous films begin to conduct at extremely low thickness, and do not exhibit complicated quasi-reentrant behavior in the evolution of superconductivity. The first appearance of superconductivity is a separation of R(T) curves at the lowest temperature attainable. In Bi this occurred at a normal state sheet resistance near h/4e squared, however in Pb and Al the separatrix was above this value. The Al film showed distinct signs of granularity which also cannot be ruled out in the Pb films, because strong suppression of the superconducting transition temperature T{sub c} make it difficult to observe properties associated with granularity. The suppression of T{sub c} is analyzed in light of theories which incorporate the effects of localization, and little agreement is found.
- Research Organization:
- Minnesota Univ., Minneapolis, MN (USA)
- OSTI ID:
- 7071795
- Resource Relation:
- Other Information: Ph.D. Thesis
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ALUMINIUM
SUPERCONDUCTIVITY
BISMUTH
LEAD
SUPERCONDUCTING FILMS
THICKNESS
ACTIVATION ENERGY
CRITICAL TEMPERATURE
EXPERIMENTAL DATA
ORDER-DISORDER TRANSFORMATIONS
TRANSITION TEMPERATURE
DATA
DIMENSIONS
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
ELEMENTS
ENERGY
FILMS
INFORMATION
METALS
NUMERICAL DATA
PHASE TRANSFORMATIONS
PHYSICAL PROPERTIES
THERMODYNAMIC PROPERTIES
360603* - Materials- Properties