Magnetic flux noise in copper oxide superconductors

Journal Article · Sat Jan 01 00:00:00 EST 1994 · Journal of Low Temperature Physics; (United States)

DOI:https://doi.org/10.1007/BF00755416· OSTI ID:5091095

Ferrari, M J; Johnson, M; Wellstood, F C; Kingston, J J; Shaw, T J; Clarke, J ^[1]

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

The authors report on the magnetic flux noise in thin films of YBa[sub 2]Cu[sub 3]O[sub 7-x] (YBCO), Tl[sub 2]Ca[sub 2]Ba[sub 2]Cu[sub 3]O[sub x], and TlCa[sub 2]Ba[sub 2]Cu[sub 3]O[sub x] and in crystals of YBCO and Bi[sub 2]Sr[sub 2]CaCu[sub 2]O[sub 8+x], measured with a Superconducting QUantum Interference Device (SQUID). They ascribe the noise to the motion of flux vortices. In the low magnetic fields in which the experiments are performed the average vortex spacing always exceeds the superconducting penetration depth. The spectral density of the noise usually scales as 1/f (f is frequency) from 1 Hz to 1 kHz and increases with temperature to a peak which is of the same magnitude in all samples, at the transition temperature. Furthermore, the noise power increases with the magnitude of the magnetic field in which the sample is cooled, with a power-law dependence over several decades, whereas a supercurrent well below the critical current density applied to YBCO films suppresses the noise power by an order of magnitude. Most of the measurements were made on YBCO films. A model of thermally activated vortex motion is developed which explains the dependence of the noise on frequency, temperature, magnetic field, and current. The pinning potential is idealized as an ensemble of symmetrical double wells, each with a different activation energy separating the two states. From the noise measurements, this model yields the distribution of pinning energies, the vortex hopping distance, the number density of mobil vortices, and the restoring force on a vortex at a typical pinning site. The distribution of pinning energies in YBa[sub 2]Cu[sub 3]O[sub 7-x] shows a broad peak below 0.1 eV. Over narrow temperature intervals, most samples exhibit random telegraph signals in which the flux switches between two discrete levels with activation energies and hopping distances much greater than those deduced from the 1/f noise measurements.

• DOE Contract Number: AC03-76SF00098
• OSTI ID: 5091095
• Journal Information: Journal of Low Temperature Physics; (United States), Vol. 94:1-2; ISSN 0022-2291
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
HIGH-TC SUPERCONDUCTORS
MAGNETIC FLUX
NOISE
BARIUM OXIDES
BISMUTH OXIDES
CALCIUM OXIDES
COPPER OXIDES
STRONTIUM OXIDES
THALLIUM OXIDES
YTTRIUM OXIDES
ALKALINE EARTH METAL COMPOUNDS
BARIUM COMPOUNDS
BISMUTH COMPOUNDS
CALCIUM COMPOUNDS
CHALCOGENIDES
COPPER COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
STRONTIUM COMPOUNDS
SUPERCONDUCTORS
THALLIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
YTTRIUM COMPOUNDS
360207* - Ceramics
Cermets
& Refractories- Superconducting Properties- (1992-)