First-principles Study of the Optical and Spin Properties of sp3-doped (6,5) Single-Walled Carbon Nanotubes

Single-walled carbon nanotubes (SWCNTs) doped with sp3 defects are a promising class of optoelectronic materials with bright tunable photoluminescence and demonstrated single-photon emission. We apply first-principles theory in combination with experimental studies to understand the optoelectronic and spin properties of sp3-defective (6,5) SWCNT containing a single unpaired spin. Density functional theory studies indicate that this unpaired spin localizes around the defect site and leads to an in-gap dispersionless state in the bandstructure of the SWCNT. Furthermore, many-body perturbation theory within the GW/BSE approximation predicts strong excitonic effects with an exciton binding energy of ~ 1 eV for both pristine and sp3-defective (6,5) SWCNT. Additionally, we simulate dephasing of the localized spin by considering spin-bath interactions as the main source of decoherence. We apply the cluster correlation expansion method with a pure-dephasing spin Hamiltonian to doped SWCNT in presence of solvent molecules at near 0 K and estimate the magnitude of the decoherence time (T₂), in good agreement with experiment.