The magnetic phase diagram of high quality superconducting YBa2Cu3O7-8 single crystals
The magnetic phase diagram of high quality superconducting YBa2Cu3O7-8 single crystals
Resistivity and a.c. susceptibility measurements have been performed on very high quality, superconducting YBa2Cu3O7-δ single crystals in applied d.c. fields of up to 14T. The measurements were conducted using purpose built rigs. The vortex lattice melting transition has been observed in both the resistivity data and a.c. susceptibility data. Furthermore, the multi-critical point was clearly observable in these data. The disordered solid state above the critical point was found not to be a vortex glass.
The effects of oxygen stoichiometry have also been investigated for detwinned YBa2Cu3O7-δ, δ<0.1. The critical point was seen to vary systematically with δ, as was the normal state resistivity. The profound effects on the magnetic phase diagram that have been observed are explained in terms of chain superconductivity reducing the anisotropy of the YBa2Cu3O7-δ system as δ tends to zero.
The evolution of the resistive peak effect has been studied at low current densities using d.c. SQUID picovoltometry. The tail of the peak effect has been shown to be due to the thermally activated plastic deformation of the vortex domain structure. Analysis has shown the activation barrier to be temperature and d.c. field independent, with some evidence that the barrier scales with driving current density.
High field a.c. susceptibility measurements on detwinned YBa2Cu3O7-δ have shown a sharp onset in the out of phase susceptibility. This onset has been correlated with the vortex lattice melting transition from resistivity measurements on the same samples. The sharp onset is seen to disappear at the critical point, being replaced by a single symmetric losses peak. A transition region about the melting transition is identified, where at low a.c. driving fields a transition from a vortex liquid to a pinned solid is observed. Furthermore, at high a.c. driving fields a transition from a the vortex liquid to a moving solid is also identified.
The excellent agreement between the critical points, as obtained from a.c. susceptibility measurements and transport measurements, show that the melting line and the critical point in the magnetic phase diagram of high quality YBa2Cu3O7-δ single crystals can be accurately obtained from a.c. susceptibility.
University of Southampton
1997
Pinfold, Steven
(1997)
The magnetic phase diagram of high quality superconducting YBa2Cu3O7-8 single crystals.
University of Southampton, Doctoral Thesis.
Record type:
Thesis
(Doctoral)
Abstract
Resistivity and a.c. susceptibility measurements have been performed on very high quality, superconducting YBa2Cu3O7-δ single crystals in applied d.c. fields of up to 14T. The measurements were conducted using purpose built rigs. The vortex lattice melting transition has been observed in both the resistivity data and a.c. susceptibility data. Furthermore, the multi-critical point was clearly observable in these data. The disordered solid state above the critical point was found not to be a vortex glass.
The effects of oxygen stoichiometry have also been investigated for detwinned YBa2Cu3O7-δ, δ<0.1. The critical point was seen to vary systematically with δ, as was the normal state resistivity. The profound effects on the magnetic phase diagram that have been observed are explained in terms of chain superconductivity reducing the anisotropy of the YBa2Cu3O7-δ system as δ tends to zero.
The evolution of the resistive peak effect has been studied at low current densities using d.c. SQUID picovoltometry. The tail of the peak effect has been shown to be due to the thermally activated plastic deformation of the vortex domain structure. Analysis has shown the activation barrier to be temperature and d.c. field independent, with some evidence that the barrier scales with driving current density.
High field a.c. susceptibility measurements on detwinned YBa2Cu3O7-δ have shown a sharp onset in the out of phase susceptibility. This onset has been correlated with the vortex lattice melting transition from resistivity measurements on the same samples. The sharp onset is seen to disappear at the critical point, being replaced by a single symmetric losses peak. A transition region about the melting transition is identified, where at low a.c. driving fields a transition from a vortex liquid to a pinned solid is observed. Furthermore, at high a.c. driving fields a transition from a the vortex liquid to a moving solid is also identified.
The excellent agreement between the critical points, as obtained from a.c. susceptibility measurements and transport measurements, show that the melting line and the critical point in the magnetic phase diagram of high quality YBa2Cu3O7-δ single crystals can be accurately obtained from a.c. susceptibility.
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Published date: 1997
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Local EPrints ID: 463162
URI: http://eprints.soton.ac.uk/id/eprint/463162
PURE UUID: dfbffa21-3b89-4438-8fed-5bf47993c695
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Date deposited: 04 Jul 2022 20:46
Last modified: 04 Jul 2022 20:46
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Author:
Steven Pinfold
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