Theory of tunneling in metal--superconductor devices: Supercurrents in the superconductor gap at zero temperature
Tunneling experiments in metal-oxide superconductor have shown the existence of ''leakage'' currents for applied voltages V smaller than one-half of the superconductor gap ..delta... These currents are independent of temperature T. Recently experiments with scanning tunneling microscopy (STM) and squeezable tunnel junctions have shown that the observation of the superconductor gap depends strongly on the resistance in the junction. In fact only for resistances larger than approx.10/sup 6/ ..cap omega.. the gap is clearly observable. These experiments have been explained in terms of the perturbative Hamiltonian formalism of Bardeen. However, it may happen that this theory while applicable for very large resistances may not be so for small tunnel resistances. We present here a nonperturbative theory in all orders of the transmitivity chemically bondTochemically bond/sup 2/ and show the existence of supercurrents for values of V<..delta.. at T = 0. This is done by performing a matching in the junction between the superconductor Bogolubov wave functions for Copper pairs and the electron and hole wave functions in the normal metal. Typical numerical results are presented for several values of chemically bondTochemically bond/sup 2/. We believe that experiments in STM and other junctions should be interpreted in the frame of this theory.
- Research Organization:
- Departamento de Fisica de la Materia Condensada, Universidad Autonoma de Madrid, Cantoblanco, 28049-Madrid, Spain
- OSTI ID:
- 5334862
- Journal Information:
- J. Vac. Sci. Technol., A; (United States), Vol. 6:2
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
SUPERCONDUCTIVITY AND SUPERFLUIDITY
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
SUPERCONDUCTING JUNCTIONS
LEAKAGE CURRENT
SCANNING ELECTRON MICROSCOPY
TUNNEL EFFECT
ELECTRIC CONDUCTIVITY
MATHEMATICAL MODELS
SUPERCONDUCTORS
CURRENTS
ELECTRIC CURRENTS
ELECTRICAL PROPERTIES
ELECTRON MICROSCOPY
JUNCTIONS
MICROSCOPY
PHYSICAL PROPERTIES
656100* - Condensed Matter Physics- Superconductivity
420201 - Engineering- Cryogenic Equipment & Devices