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
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|
|Thesis Availability:||Restricted to Caltech community only|
|Defense Date:||17 October 2002|
|Default Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Imported from ETD-db|
|Deposited On:||24 Oct 2002|
|Last Modified:||26 Dec 2012 03:06|
- Final Version
Restricted to Caltech community only
See Usage Policy.
Repository Staff Only: item control page