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Spin-polarized quasiparticle transport in cuprate superconductors

Citation

Fu, Chu-Chen (2003) Spin-polarized quasiparticle transport in cuprate superconductors. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechETD:etd-10242002-021518

Abstract

The effects of spin-polarized quasiparticle transport in superconducting YBa2Cu3O(7-d) (YBCO) epitaxial films are investigated by means of current injection into perovskite ferromagnet-insulator-superconductor (F-I-S) heterostructures. Transport and magnetic properties of these CMR perovskites are first investigated by inducing lattice distortions using lattice mismatching substrates. The half-metallic nature of these perovskites provides an epitaxially grown heterostructure, ideal for injection of spin-polarized current. These effects are compared with the injection of simple quasiparticles into control samples of perovskite non-magnetic metal-insulator-superconductor (N-I-S). Systematic studies of the critical current density (Jc) as a function of the injection current density, temperature, and the thickness of the superconductor demonstrate the "self-injection effect" and reveal dramatic differences between the F-I-S and N-I-S heterostructures, with strong suppression of Jc and a rapidly increasing characteristic transport length near the superconducting transition temperature Tc only in the F-I-S samples. The temperature dependence of the efficiency in the F-I-S samples is also in sharp contrast to that in the N-I-S samples, suggesting significant redistribution of quasiparticles in F-I-S due to the longer lifetime of spin-polarized quasiparticles. Application of conventional theory for nonequilibrium superconductivity to these data further reveals that a substantial chemical potential shift in F-I-S samples must be invoked to account for the experimental observation, whereas no discernible chemical potential shift exists in the N-I-S samples, suggesting strong effects of spin-polarized quasiparticles on cuprate superconductivity. The characteristic times estimated from our studies are suggestive of anisotropic spin relaxation processes, possibly with spin-orbit interaction dominating the c-axis spin transport and exchange interaction prevailing within the CuO2 planes.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Nonequilibrium superconductivity; spin-injection; YBCO
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Physics
Thesis Availability:Restricted to Caltech community only
Research Advisor(s):
  • Yeh, Nai-Chang
Thesis Committee:
  • Yeh, Nai-Chang (chair)
  • Zmuidzinas, Jonas
  • Cross, Michael Clifford
  • Tombrello, Thomas A.
Defense Date:17 October 2002
Record Number:CaltechETD:etd-10242002-021518
Persistent URL:http://resolver.caltech.edu/CaltechETD:etd-10242002-021518
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:4227
Collection:CaltechTHESIS
Deposited By: Imported from ETD-db
Deposited On:24 Oct 2002
Last Modified:26 Dec 2012 03:06

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