Spin-polarized quasiparticle transport in cuprate superconductors

TL;DR

This study investigates how spin-polarized quasiparticles affect superconductivity in YBCO films, revealing significant suppression of critical currents and anisotropic spin relaxation processes, with implications for understanding spin transport in high-Tc superconductors.

Contribution

It provides the first detailed experimental analysis of spin-polarized quasiparticle transport effects in cuprate superconductors, highlighting differences from non-magnetic injection and proposing anisotropic spin relaxation mechanisms.

Findings

Strong suppression of critical current in F-I-S heterostructures.

Rapid increase in transport length near Tc in F-I-S samples.

Evidence of anisotropic spin relaxation processes.

Abstract

The effects of spin-polarized quasiparticle transport in superconducting YBa2Cu3O_{7-\delta} (YBCO) epitaxial films are investigated by means of current injection into perovskite ferromagnet-insulator-superconductor (F-I-S) heterostructures. 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 as a function of the injection current density, temperature and the thickness of the superconductor reveal drastic differences between the F-I-S and N-I-S heterostructures, with strong suppression of the critical currents and a rapidly increasing characteristic transport length near the superconducting transition temperature only in the F-I-S samples. The temperature dependence of the injection efficiency in the F-I-S samples is also in sharp contrast to that in the N-I-S samples. 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. Several alternative scenarios attempted to account for the suppression of critical currents in F-I-S samples are also critically examined, and are found to be neither compatible with experimental data nor with the established theory of nonequilibrium superconductivity.