Oscillating spin Hall effect from polaron transport in organic chains

Abstract

The polaron dynamics in organic ladders is calculated in the presence of electron-lattice and spin-orbit couplings (SOCs), employing an extended Su-Schrieffer-Heeger (SSH) model and a nonadiabatic dynamics method. The time-dependent total charge and spin in the chains is averaged over initial polaron states with spins up and down. This average reveals a strong oscillating spin Hall effect (SHE). We show the necessity of all terms in the SSH Hamiltonian for the SHE, including intrachain and interchain hopping as well as intrachain and interchain SOC. The large and rapidly oscillating behavior of the SHE is verified to originate from the existence of polarons by comparison with the case of rigid chains without polarons. We attribute the enhancement of the SHE to skew scattering off transient deformations of the chains. Spectral analysis exhibits three dominant parts in the Fourier-transformed spin Hall signal. The high-frequency part is associated with the pure spin-flip dynamics due to SOC, while the low-frequency parts, which are also observed in the charge response, are related to the intrinsic electron transfer between the chains and the appearance of polarons, respectively. In this paper, we reveal the distinct properties of the dynamical SHE in organics dominated by polaron transport.