Spin Relaxation Mechanism in a Highly Doped Organic Polymer Film

TL;DR

This study investigates spin transport and relaxation in highly doped organic polymer films, revealing that spin relaxation mainly occurs due to spin-orbit coupling at nanoscale grains, with a long spin diffusion length.

Contribution

It provides the first systematic measurement of spin diffusion length, spin lifetime, and diffusion constant in highly doped organic semiconductors using multiple experimental techniques.

Findings

Spin lifetime is shorter than previously expected.

Large spin diffusion constant explained by hopping transport.

Spin angular momentum is preserved during hopping events.

Abstract

We report the systematic studies of spin current transport and relaxation mechanism in highly doped organic polymer film. In this study, we have determined spin diffusion length (SDL), spin lifetime, and spin diffusion constant by using different experimental techniques. The spin lifetime estimated from the electron paramagnetic resonance experiment is much shorter than the previous expectation beyond the experimental ambiguity. This suggests that significantly large spin diffusion constant, which is reasonably explained by the hopping transport mechanism in degenerate semiconductors, exists in highly doped organic semiconductors. The calculated SDL using the spin lifetime and spin diffusion constant estimated from our experiment is comparable to the experimentally obtained SDL of the order of one hundred nanometers. Moreover, the present study revealed that the spin angular momentum is almost preserved in the hopping events. In other words, the spin relaxation mainly occurs due to the spin-orbit coupling at the nanoscale crystalline grains.