Dependence of Phase Diagram of BSCCO on Disorder and Anisotropy

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" Dependence of Phase Diagram of BSCCO on Disorder and Anisotropy "
Tal Verdene E. Zeldov

Document Type	:	Latin Dissertation
Language of Document	:	English
Record Number	:	55411
Doc. No	:	TL25365
Call number	:	‭3461760‬
Main Entry	:	Tal Verdene
Title & Author	:	Dependence of Phase Diagram of BSCCO on Disorder and Anisotropy\ Tal Verdene
College	:	The Weizmann Institute of Science (Israel)
Date	:	2008
Degree	:	Ph.D.
student score	:	2008
Page No	:	72
Abstract	:	In this work we studied the B–T phase diagram of vortex matter in high-Tc and low-T c type II superconductors. First and second order phase transitions of vortex matter in the layered high-Tc superconductor Bi2Sr2CaCu2O8 were mapped using local magnetization measurements with micro Hall-sensor arrays. The equilibrium measurements down to ∼ 27K were obtained by utilization of the shaking method, in which an in-plane ac field is applied to relax vortices to their equilibrium configuration. Transport measurements were performed in order to study the dynamic behavior of vortex matter in the low- Tc superconductor NbSe2. Measurements of the self-field induced by ac current in the new superconductor MgB2 were performed within the study of its edge and bulk related mechanisms. We present thermodynamic evidence for new first-order - second-order - first-order behavior of the melting line in BSCCO samples irradiated with a low density of columnar defects. This unusual behavior is due to close competition between four different energy scales in the dilute columnar defects limit. As columnar defects are introduced, the melting transition initially alters its order from first to second at intermediate temperatures where correlated pinning has a dominant effect. At high and low temperatures the transition remains first-order despite the disordering potential of columnar defects. As the density of the columnar defects is increased, the second-order segment of the transition line expands both to the higher and lower temperatures. The observed nucleation and growth process of the second-order segment along the original first-order transition line clarifies the general process of transformation of phase transitions with increased disorder. We found that disorder and thermal-fluctuations weaken relative to elasticity with increased oxygen doping, which shifts the first-order melting line towards higher fields. Disorder still gains relative dominance over thermal fluctuations, which concurrently shifts the maximum of the first-order line and its bisection with the second-order line towards higher temperatures. We present evidence which suggest that the disordered metastable states near the peak effect of the critical current in NbSe2 are enhanced by the presence of columnar defects. Whether this enhancement occurs predominantly at the edges of the sample and is linked to the edge contamination mechanism or in the bulk of the sample remains an open question for future investigation.
Subject	:	Applied sciences; Pure sciences; BSCCO; Phase diagram; Superconductors; Vortex matter; Condensed matter physics; Materials science; 0611:Condensed matter physics; 0794:Materials science
Added Entry	:	E. Zeldov
Added Entry	:	The Weizmann Institute of Science (Israel)