Ac susceptibility and resistivity studies of YBa2Cu3O7-8 high-temperature superconductors
Ac susceptibility and resistivity studies of YBa2Cu3O7-8 high-temperature superconductors
Detailed ac susceptibility and resistivity measurements have been carried out using purpose built equipment and in dc fields of up to 12 T, on high quality, superconducting YBa2Cu3O7-δ single crystals.
Comparative measurements of the ac susceptibility and resistivity have detected corresponding signatures of the vortex melting transition at a temperature Tm. The ac susceptibility data suggest that just below Tm, there is a transition region where the liquid and solid phases coexist. The width of this region was found to be sample dependent and can be related to structural inhomogeneity.
Detailed studies of the E-J characteristics across the transition region have been performed using a sensitive superconducting quantum interference device picovoltmeter. It was found that within the transition region the system could be switched from a lower to a higher resistivity state by applying a current in excess of a threshold value. We interpret this observation in terms of a rearrangement of solidified vortex domains.
Ac susceptibility measurements have been performed on several twinned and detwinned YBa2Cu3O7-δ single crystals, at low and high dc fields. In the low dc field case, a linear vortex response was found for low amplitudes of applied ac field. In this regime the vortex response was frequency independent and satisfactorily described by a Campbell regime of pinned vortices. For higher amplitudes, a non-linear vortex response developed, affected by both Campbell and flux creep contributions. At high dc fields and low amplitudes of the ac field, a mixture of Ohmic and Campbell regimes were found. As the amplitude increased the Campbell contribution becomes less important and the amplitude of the dissipation increased, indicating a flux-flow Ohmic regime.
Finally, experimental evidence has been provided for the suppression of first order melting by twin boundary pinning. In the presence of such pinning, the temperature dependence of the ac susceptibility became very similar to the second order transition observed in the high field case (μ0H=10 T).
University of Southampton
1999
Bracanovic, Darko
(1999)
Ac susceptibility and resistivity studies of YBa2Cu3O7-8 high-temperature superconductors.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Detailed ac susceptibility and resistivity measurements have been carried out using purpose built equipment and in dc fields of up to 12 T, on high quality, superconducting YBa2Cu3O7-δ single crystals.
Comparative measurements of the ac susceptibility and resistivity have detected corresponding signatures of the vortex melting transition at a temperature Tm. The ac susceptibility data suggest that just below Tm, there is a transition region where the liquid and solid phases coexist. The width of this region was found to be sample dependent and can be related to structural inhomogeneity.
Detailed studies of the E-J characteristics across the transition region have been performed using a sensitive superconducting quantum interference device picovoltmeter. It was found that within the transition region the system could be switched from a lower to a higher resistivity state by applying a current in excess of a threshold value. We interpret this observation in terms of a rearrangement of solidified vortex domains.
Ac susceptibility measurements have been performed on several twinned and detwinned YBa2Cu3O7-δ single crystals, at low and high dc fields. In the low dc field case, a linear vortex response was found for low amplitudes of applied ac field. In this regime the vortex response was frequency independent and satisfactorily described by a Campbell regime of pinned vortices. For higher amplitudes, a non-linear vortex response developed, affected by both Campbell and flux creep contributions. At high dc fields and low amplitudes of the ac field, a mixture of Ohmic and Campbell regimes were found. As the amplitude increased the Campbell contribution becomes less important and the amplitude of the dissipation increased, indicating a flux-flow Ohmic regime.
Finally, experimental evidence has been provided for the suppression of first order melting by twin boundary pinning. In the presence of such pinning, the temperature dependence of the ac susceptibility became very similar to the second order transition observed in the high field case (μ0H=10 T).
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Published date: 1999
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Local EPrints ID: 463998
URI: http://eprints.soton.ac.uk/id/eprint/463998
PURE UUID: d1a55f6d-0eb0-4eac-906e-48443e3a44e9
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Date deposited: 04 Jul 2022 21:00
Last modified: 04 Jul 2022 21:00
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Author:
Darko Bracanovic
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