Transport and microwave properties of YBa[sub 2]Cu[sub 3]O[sub 7[minus]x] superconducting films

Miscellaneous · Wed Jan 01 00:00:00 EST 1992

OSTI ID:7303107

Jiang, H

High quality YBCO c-axis oriented films were made by a laser ablation technique. Josephson weak links were fabricated on a modified microbridge by using bicrystal YBCO films. Shapiro steps were observed on modified microbridge weak links. Vortex ring nucleation by thermal activation and quantum tunneling processes in high T[sub c] superconductors is discussed. The nonlinear resistance scales as e[sup [minus]](J[sub v]/J)[sup v]. Thermal activation yields a critical index of v = 1, while quantum tunneling (without normal current dissipation) yields v = 2. I-V characteristics were measured on both disordered (low J[sub c]), ordered (high J[sub c]) YBCO films and microbridges below T[sub c]. The data were examined in terms of both thermal activation and quantum tunneling models. Intrinsic critical current densities in high T[sub c] superconducting films are discussed. The enhancement of the quantum electrodynamic tunneling process due to normal current dissipation is proposed to explain the measured J[sub c] results for YBCO films. The limitation of J[sub c] appears to be due to vortex ring creation. Studying J[sub c] of bridge constrictions was a way to approach the depairing current limit. A novel microwave self-resonant (MSR) technique was developed to measure surface resistance, R[sub 8], of YBCO superconducting films directly and surface reactance, X[sub 8], indirectly. R[sub 8] at 21 GHz decreased by about three orders of magnitude as the temperature decreased from 90K to 80K. The smallest surface resistance was 2.7 [times] 10[sup [minus]4][Omega] at 21 GHz and at 15K, and the surface reactance was 0.031[Omega]. Using the MSR technique, the authors measured the London penetration depth and coherence length, and found that both [lambda] and [xi] were anisotropic, their values depended on the direction of the microwave electric field relative to the c-axis.

• Research Organization: Northeastern Univ., Boston, MA (United States)
• OSTI ID: 7303107
• Resource Relation: Other Information: Thesis (Ph.D.)
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
SUPERCONDUCTING FILMS
ELECTRICAL PROPERTIES
TUNNEL EFFECT
BARIUM OXIDES
CUPRATES
CURRENT DENSITY
ELECTRIC BRIDGES
ELECTRIC CONDUCTIVITY
HIGH-TC SUPERCONDUCTORS
INTERMETALLIC COMPOUNDS
JOSEPHSON JUNCTIONS
MICROWAVE RADIATION
YTTRIUM OXIDES
ALKALINE EARTH METAL COMPOUNDS
ALLOYS
BARIUM COMPOUNDS
CHALCOGENIDES
COPPER COMPOUNDS
ELECTRICAL EQUIPMENT
ELECTROMAGNETIC RADIATION
EQUIPMENT
FILMS
JUNCTIONS
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
RADIATIONS
SUPERCONDUCTING JUNCTIONS
SUPERCONDUCTORS
TRANSITION ELEMENT COMPOUNDS
YTTRIUM COMPOUNDS
360207* - Ceramics
Cermets
& Refractories- Superconducting Properties- (1992-)