The dominant spin relaxation mechanism in compound organic semiconductors

TL;DR

This paper investigates the primary spin relaxation mechanism in organic semiconductors, providing evidence that spin-orbit interaction via the Elliott-Yafet mechanism, rather than hyperfine interactions, dominates spin relaxation.

Contribution

It presents experimental data on electric-field dependence of spin diffusion length, challenging previous assumptions and identifying the Elliott-Yafet mechanism as the main relaxation process.

Findings

Spin diffusion length depends on electric field.

Temperature dependence data contradict hyperfine interaction dominance.

Elliott-Yafet mechanism is more consistent with observed data.

Abstract

Despite the recent interest in "organic spintronics", the dominant spin relaxation mechanism of electrons or holes in an organic compound semiconductor has not been conclusively identified. There have been sporadic suggestions that it might be hyperfine interaction caused by background nuclear spins, but no confirmatory evidence to support this has ever been presented. Here, we report the electric-field dependence of the spin diffusion length in an organic spin-valve structure consisting of an Alq3 spacer layer, and argue that this data, as well as available data on the temperature dependence of this length, contradict the notion that hyperfine interactions relax spin. Instead, they suggest that the Elliott-Yafet mechanism, arising from spin-orbit interaction, is more likely the dominant spin relaxing mechanism.