Aspects of Nodal Quasiparticle Transport in High-Tc Superconductors [microform]
Aspects of Nodal Quasiparticle Transport in High-Tc Superconductors [microform]

Author: Michael F. (Michael Francis) Smith

Publisher: Library and Archives Canada = Bibliothèque et Archives Canada

Published: 2005

Total Pages: 240

ISBN-13: 9780494028902

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Various low-temperature thermodynamic and transport properties of high TC superconductors at temperatures well below TC are studied theoretically under the assumption that the low-energy excited states can be regarded as independent Bogolubov quasiparticles near the nodes of the superconducting order parameter. In the limiting case of temperatures well above that corresponding to the impurity scattering rate, a Boltzmann-equation description of the quasiparticle distribution is used to study thermal and electrical transport for several scattering mechanisms. In particular, the dominant scattering mechanism for the relaxation of microwave electrical currents well below TC is identified, and the observed temperature dependence of the microwave conductivity data in optimally-doped YBa2Cu3O7-delta thus explained. The Knight shift and nuclear spin relaxation rate at temperatures well above the impurity scattering rate are also calculated and compared with available data. In the opposite limiting case of temperatures well below that corresponding to the impurity scattering rate, the sound attenuation and electron-phonon heat transfer rate are calculated. A model for the electron-phonon interaction in square-lattice tight-binding materials is developed and used to explain the huge measured anisotropy of the normal-state sound attenuation in the unconventional superconductor Sr2RuO4 and to rule out certain candidates for the order parameter symmetry of this material. A calculation of the electron-phonon heat transfer rate for d-wave superconductors gives the dependence of this quantity on various material parameters. Finally, the result for the electron-phonon heat transfer rate is used to explain the origin of the anomalous downturns in the thermal conductivity that have been observed in both the normal and superconducting state of cuprate superconductors, most notably in Pr2-xCe xCuO7-delta.

Transport Properties of Chiral P-wave Superconductor-normal Metal Nanostructures
Transport Properties of Chiral P-wave Superconductor-normal Metal Nanostructures

Author: Ahmet Keles

Publisher:

Published: 2014

Total Pages: 67

ISBN-13:

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In this thesis, we present a theory of electron transport for unconventional superconductors. We focus on the superconducting properties of Sr2RuO4, which is a strong candidate for two dimensional p-wave superconductivity in electronic systems. We present Green function formulation of the theory of superconductivity and reduce the formulation within quasiclassical approximation. To study the systems with disordered normal metal junctions, we derive the boundary conditions of quasiclassical equations from the microscopic theory considering a spin active boundary. Boundary between normal metal and superconductor is modeled with Rashba type spin orbit coupling. An exact solution of the resulting equations are given and the resistance of the model system is calculated as a function of temperature, boundary transparency and superconducting state symmetry. The developed theory is used to study the phase transition of unconventional superconductors with increasing impurity concentration. It has been shown that, in the strong disordered regime, system can be modeled as Mattis model known from the theory of spin glasses. We show that with increasing disorder there will be two consecutive phase transitions: A phase transition from unconventional superconductor to s-wave superconductor followed by a transition from s-wave superconductor to normal metal. A qualitative phase diagram is prsented and corrections to Mattis model approximation is considered.

{Open_quotes}Local Texture, Current Flow, and Superconductive Transport Properties of Tl1223 Deposits on Practical Substrates{close_quotes}
{Open_quotes}Local Texture, Current Flow, and Superconductive Transport Properties of Tl1223 Deposits on Practical Substrates{close_quotes}

Author:

Publisher:

Published: 1996

Total Pages: 5

ISBN-13:

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Quantitative investigations of the crystal grain orientations and electrical transport properties of high temperature superconducting (HTS)TiBa2Ca2Cu3O{sub 8+x} (Tl1223) deposits on polycrystalline substrates show that current flow comprises percolative networks of strongly-coupled material. Superconductive transport properties on different samples, on the same samples at different widths, and on samples with artificially-induced strong flux pinning defects confirm the nature of current flow, and suggest that these materials may be useful as a new class of HTS conductors.