Jiang, Wen (1995) Effects of controlled disorder on the vortex phases of high-temperature superconductors. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-06212007-152240
The high transition temperature, short coherence length and long penetration depth of high-temperature superconductors result in novel vortex properties associated with the large thermal and disorder fluctuations. This thesis presents systematic experimental investigations on the vortex phases of YBa2Cu3O7 single crystals with different types of controlled disorder. Measurements of dc current-voltage characteristics and ac impedance as a function of frequency are carried out on dilutely twinned YBa2Cu3O7 single crystals irradiated with 3.0 MeV protons. It is found that the moderately increased vortex pinning caused by the increasing density of controlled point defects does not change the nature of the second-order vortex-glass transitions in YBa2Cu3O7 single crystals with dilute twin boundaries, as manifested by the universal critical exponents and scaling functions for samples with different densities of point defects. In YBa2Cu3O7 single crystals with c-axis correlated columnar defects created by 0.9 GeV Pb-ion irradiation, a Bose-glass to "superfluid" transition is demonstrated by the universal critical scaling behavior of the ac impedance versus frequency isotherms. The static and dynamic critical exponents and the universal scaling functions are determined from our self-consistent critical scaling analyses. The Bose-glass transition temperature is found to decrease with the increasing angle between the applied magnetic field and the column orientation, in contrast to the angular dependence of the vortex-glass transition temperature which increases monotonically with the increasing angle due to the intrinsic sample anisotropy.
The interplay of vortex pinning and thermodynamic vortex phase transitions is further studied in the weak pinning limit by investigating the vortex transport properties of a nearly defect-free, untwinned YBa2Cu3O7 single crystal. Two novel phenomena are observed and studied quantitatively. The resistive hysteresis near the vortex-solid melting transition is ascribed to a current-induced non-equilibrium effect; the resistive "peak effect" below the vortex-solid transition is found to be a general phenomenon existing in extreme type-II superconductors, and is associated with the softening of the vortex-solid before the thermodynamic melting transition. It is therefore concluded that the current-induced effects are of particular importance in determining the vortex properties of extreme type-II superconductors with weak pinning.
|Item Type:||Thesis (Dissertation (Ph.D.))|
|Degree Grantor:||California Institute of Technology|
|Division:||Physics, Mathematics and Astronomy|
|Thesis Availability:||Restricted to Caltech community only|
|Defense Date:||15 May 1995|
|Default Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Imported from ETD-db|
|Deposited On:||18 Jul 2007|
|Last Modified:||26 Dec 2012 02:53|
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