Separating hyperfine from spin-orbit interactions in organic semiconductors by multi-octave magnetic resonance using coplanar waveguide microresonators

TL;DR

This study introduces a multi-octave magnetic resonance technique using coplanar waveguide microresonators to distinguish hyperfine from spin-orbit interactions in organic semiconductors, revealing subtle effects of spin-orbit coupling across a broad frequency range.

Contribution

The paper presents a novel multi-octave resonator setup for electrically detected magnetic resonance, enabling detailed analysis of spin interactions in organic semiconductors.

Findings

Spin-orbit interactions cause broadening of resonance spectra at higher frequencies.

Resonators cover nearly five octaves in frequency within a single setup.

Small but significant effects of spin-orbit coupling are observed.

Abstract

Separating the influence of hyperfine from spin-orbit interactions in spin-dependent carrier recombination and dissociation processes necessitates magnetic resonance spectroscopy over a wide range of frequencies. We have designed compact and versatile coplanar waveguide resonators for continuous-wave electrically detected magnetic resonance, and tested these on organic light-emitting diodes. By exploiting both the fundamental and higher-harmonic modes of the resonators we cover almost five octaves in resonance frequency within a single setup. The measurements with a common pi-conjugated polymer as the active material reveal small but non-negligible effects of spin-orbit interactions, which give rise to a broadening of the magnetic resonance spectrum with increasing frequency.