Equilibrium vortex motion in two- and three-dimensional superconductors studied with a dc SQUID

Thesis/Dissertation · Wed Oct 01 00:00:00 EDT 1997

DOI:https://doi.org/10.2172/578751· OSTI ID:578751

Shaw, Timothy J. ^[1]

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1. Univ. of California, Berkeley, CA (United States). Dept. of Physics

The equilibrium motion of vortices in two- and three-dimensional superconductors has been studied with a dc Superconducting QUantum Interference Device (SQUID). This technique has the advantage of probing the system in a non-invasive manner as well as providing dynamic information over many decades in frequency. Through measurements of the spectral density of magnetic flux noise, S_Ψ(ω), as a function of temperature and applied magnetic field, the effects of proton and heavy ion irradiation on flux noise in crystals of YBa₂Cu₃O_7-δ have been measured and compared with the effects on the critical current, J_c. Both proton and heavy ion irradiation proved effective at reducing S_Ψ(ω), with proton irradiation having a larger effect. Measurement of S_Ψ(ω) due to the equilibrium Kosterlitz-Thouless-Berezinskii transition in two-dimensional Josephson Junction Arrays (JJAs) was studied as a function of temperature for three different arrays and using three different sensors. S_Ψ is shown to obey dynamic scaling over as many as five decades in frequency, and estimates are made for the dynamic critical exponent z. An analytic theory for the high- and low-frequency behavior of S_Ψ(ω) is presented and compared to the measured data, with the result that the low-frequency behavior is well described by the theory but the high-frequency behavior is not. Other theories and numerical simulations are described and compared with the data, but none are completely satisfactory. Lastly, suggestions for necessary further theoretical work and possible future experimental work are suggested.

• Research Organization: Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 578751
• Report Number(s): LBNL-40923; ON: DE98051535; TRN: 98:004383
• Resource Relation: Other Information: TH: Thesis (Ph.D.); PBD: Oct 1997
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
MAGNETIC FLUX
YTTRIUM OXIDES
BARIUM OXIDES
COPPER OXIDES
PHYSICAL RADIATION EFFECTS
JOSEPHSON JUNCTIONS
SQUID DEVICES
RESEARCH PROGRAMS
CRITICAL CURRENT
TEMPERATURE DEPENDENCE
KOSTERLITZ-THOULESS THEORY