Effect of Charge Localization on the Effective Hyperfine Interaction in Organic Semiconducting Polymers

Organic semiconductors (OSECs) possess weak spin-orbit coupling and hyperfine interaction (HFI); therefore, their spin lifetimes are incredibly long for spin based devices including qubits. In this talk, we will show that the spin lifetime in OSECs can be further prolonged by improving the charge delocalization. HFI, originating from the coupling between electron spins and nuclei, has been demonstrated to strongly influence the spin dynamics in OSECs. Nevertheless, the role of charge localization on the HFI strength in organic thin films has not yet been experimentally investigated. In our PRL (120, 086602, 2018), the statistical relation hypothesis that the effective HFI of holes in regioregular poly(3-hexylthiophene) (P3HT) is proportional to 1/N^0.5 has been examined, where N is the number of the random nuclear spins within the envelope of the hole wave function. First, we verify that HFI is the dominant spin interaction in P3HT. Second, assuming that holes delocalize fully over the P3HT polycrystalline domain, the strength of HFI is experimentally demonstrated to be proportional to 1/N^0.52 in excellent agreement with the statistical relation. Finally, the HFI of electrons in P3HT is about 3 times stronger than that of holes due to the stronger localization of the electrons.