Point-contact tunneling in monophasic and polyphasic Y-Ba-Cu-O samples: Experiment and model

Journal Article · Wed Feb 01 04:00:00 EST 1989 · Phys. Rev. B: Condens. Matter; (United States)

DOI:https://doi.org/10.1103/PhysRevB.39.2261· OSTI ID:6552479

Gonnelli, R S; Andreone, D; Lacquaniti, V; Abbattista, F; Vallino, M

Tunneling experiments using large-area point-contact structures have been performed on several monophasic polycrystalline Ba/sub 2/Cu/sub 3/O/sub 7-//sub delta/ samples and on polyphasic samples containing, mixed with the previous superconducting phase, also about 11% of the so-called green phase (BaY/sub 2/CuO/sub 5/). Both niobium and Y-Ba-Cu-O tips were used as counterelectrodes and measurements were made at 4.2 and 77 K. Results obtained at different experimental conditions show great reproducibility indicating the presence of the gap voltage at about 20 mV in the dynamic resistance curves. A phenomenological model was then developed to interpret in a quantitative way our data by means of a decomposition of the experimental conductance into a background component and a superconducting-tunneling component. The former results essentially in a parabolic contribution versus the bias voltage typical of a tunneling between normallike junction electrodes while the latter component is smeared out in voltage by a large amount of broadening. Using the model in a least-squares fit of the experimental data of Nb/Y-Ba-Cu-O junctions, values V/sub G/ = 21.3 +- 0.8 mV and V/sub G/ = 22.0 +- 0.6 mV for the voltage gaps at 4.2 K of monophasic and polyphasic materials, respectively, have been determined. These results have been well confirmed by measurements on Y-Ba-Cu-O/Y-Ba-Cu-O junctions while, at 77 K, there are no indications of a superconducting tunneling. We obtained also the parameters of the background conductance, which indicates the presence of a nonsuperconducting layer at the surface of the material.

• Research Organization: Dipartimento di Fisica, Politecnico di Torino, Torino, Italy
• OSTI ID: 6552479
• Journal Information: Phys. Rev. B: Condens. Matter; (United States), Journal Name: Phys. Rev. B: Condens. Matter; (United States) Vol. 39:4; ISSN PRBMD
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360204* -- Ceramics
Cermets
& Refractories-- Physical Properties
656100 -- Condensed Matter Physics-- Superconductivity
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ALKALINE EARTH METAL COMPOUNDS
BARIUM COMPOUNDS
BARIUM OXIDES
CHALCOGENIDES
COPPER COMPOUNDS
COPPER OXIDES
CRYSTALS
ELECTRIC CONDUCTIVITY
ELECTRIC CONTACTS
ELECTRICAL EQUIPMENT
ELECTRICAL PROPERTIES
ENERGY GAP
EQUIPMENT
LOW TEMPERATURE
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
POLYCRYSTALS
STRUCTURAL MODELS
SUPERCONDUCTIVITY
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENT COMPOUNDS
TRANSITION TEMPERATURE
TUNNEL EFFECT
ULTRALOW TEMPERATURE
YTTRIUM COMPOUNDS
YTTRIUM OXIDES