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Title:High frequency studies of the organic superconductor kappa-bis-ethylenedithio cuprous dicyanonitrobromide
Author(s):Tea, Nim Hak
Doctoral Committee Chair(s):Salamon, Myron B.
Department / Program:Physics
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Physics, Condensed Matter
Abstract:We report measurements of the rf vortex penetration depth $\lambda$(B) of the organic compound, $\kappa$-ET$\sb2$Cu$\lbrack$N(CN)$\sb2\rbrack$Br as a function of temperature, magnetic field, and the angle made by the applied magnetic field with the ac-planes of the crystal. For$\rm\vec B\sb{dc}$$\perp$ planes, we show that the crossover B$\sp{*}$ can be described quantitatively by the 3D Lindemann melting theory; thus, it corresponds to the melting of the vortex lattice in $\kappa$-(ET)$\sb2$Cu$\lbrack$N(CN)$\sb2\rbrack$Br and lies very close to the irreversibility line. This is the first experimental evidence for vortex lattice melting in the ET family of organic superconductors. In the vortex-liquid state, we argue that the saturation of the vortex penetration depth in a magnetic field results from the finite size of the sample. Our results do not have the scaling form predicted by the the Coffey-Clem model in contrast to previous findings.
For $\rm\vec B\sb{dc}\parallel$ planes, the field penetrates the sample in the form of Josephson vortices (no normal core). We present results on the electrodynamics of Josephson vortices as a function of magnetic field and temperature. No crossover is observed with increasing magnetic field at any temperature. This is consistent with the theoretical prediction that strong intrinsic pinning inhibits the melting of the vortex lattice. We identify the transition from a single-vortex pinning to a new flux pinning regime.
When $\rm\vec B\sb{dc}$ is slightly tilted away from the ac-plane, there is an unusual broad peak in $\Delta\lambda$(H) which can be understood in terms of the huge pinning anisotropy and intrinsic pinning due to the layered structure of the organic superconductors. The results are in excellent agreement with recent ac-magnetization results on a different organic superconductor which belongs to the same family.
Issue Date:1995
Rights Information:Copyright 1995 Tea, Nim Hak
Date Available in IDEALS:2011-05-07
Identifier in Online Catalog:AAI9624509
OCLC Identifier:(UMI)AAI9624509

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