Optical readout of singlet fission biexcitons with photoluminescence detected magnetic resonance

TL;DR

This study demonstrates optical detection of spin states in singlet fission systems via photoluminescence detected magnetic resonance, revealing detailed spin dynamics and polarization, advancing quantum information applications.

Contribution

It introduces a method to optically read out and analyze spin states in singlet fission materials using ODMR, providing new insights into triplet pair dynamics and spin polarization.

Findings

Resonant ODMR transitions observed for triplet and quintet states.

Zero-field parameters characterized for each spin sublevel.

Unusual excitation intensity dependence affecting ODMR signals.

Abstract

Molecular spin systems based on photoexcited triplet pairs formed via singlet fission (SF) are attractive as carriers of quantum information because of their potentially pure and controllable spin polarization, but developing systems that offer optical routes to readout as well as initialization is challenging. Herein, we characterize the electron spin magnetic resonance change in photoluminescence intensity for a tailored organic molecular crystal while sweeping a microwave drive up to 10 GHz in a broadband loop structure. We observe resonant transitions for both triplet and quintet spin sublevel populations showing their optical sensitivity, and revealing zero-field parameters for each. We map the evolution of these spectra in both microwave frequency and magnetic field, producing a pattern of optically-detected magnetic resonance (ODMR) peaks. Fits to this data using a suitable model suggest significant spin polarization in this system with orientation selectivity. Unusual excitation intensity dependence is also observed, which inverts the sign of the ODMR signal for triplet features, but not for quintet. These observations demonstrate optical detection of the spin sublevel population dictated by SF and intermolecular geometry, and provide unique insight into the dynamics of triplet pairs.