Cooperative flux pinning in single crystals of YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}}
- Research Reactor and Department of Physics and Astronomy, University of Missouri, Columbia, Missouri 65211 (United States)
We have investigated thermally activated magnetic flux creep in single crystals of superconducting YBa{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} in the low-field, low-temperature regime of the {ital H},{ital T} phase diagram where flux motion is expected to occur via individual fluxoid jumps. Between 5 and 15 K the creep data are accurately described by a current-dependent activation barrier of the form {ital U}({ital j}){proportional_to}{ital j}{sup {minus}{mu}}, with {mu}=1.20{plus_minus}0.12. The functional form for {ital U}({ital j}) can be understood within the framework of cooperative pinning models that ascribe fluxoid pinning to the collective effects of a large number of weak-pinning defects. We argue that the appropriate extension of scaling arguments to the {open_quote}{open_quote}individual fluxoid{close_quote}{close_quote} regime implies {mu}{approx_equal}1.0, as measured. Some successful features of the model include (1) a natural interpretation for the measured {open_quote}{open_quote}four-volume{close_quote}{close_quote} {ital VX}, the volume of the moving flux bundle times the mean distance to the pinning barrier (this interpretation leads to a value for the length of a fluxoid segment that can move in a single activated jump; the shortest length observed in our experiments is approximately 75 nm); (2) an explicit correction for the temperature dependence of {ital U}({ital j}) that agrees with experiment; (3) a physically plausible value for the {open_quote}{open_quote}flux velocity{close_quote}{close_quote} {ital v}{sub {ital f}}{approx_equal}1000 m/sec; and (4) a satisfactory description of the temperature dependence of the {open_quote}{open_quote}critical current{close_quote}{close_quote} {ital j}{sub {ital c}} between 5 and 15 K. For self-consistency the concentration of pinning defects must be greater than 3{times}10{sup 19} cm{sup {minus}3}, and oxygen vacancies are the likely candidates. (Abstract Truncated)
- Research Organization:
- Purdue Research Foundation
- DOE Contract Number:
- FG02-90ER45427
- OSTI ID:
- 285636
- Journal Information:
- Physical Review, B: Condensed Matter, Journal Name: Physical Review, B: Condensed Matter Journal Issue: 1 Vol. 54; ISSN 0163-1829; ISSN PRBMDO
- Country of Publication:
- United States
- Language:
- English
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