Two-dimensional electronic spectroscopy reveals the dynamics of phonon-mediated excitation pathways in semiconducting single-walled carbon nanotubes

Electronic two-dimensional Fourier transform (2D-FT) spectroscopy is applied to semiconducting single-walled carbon nanotubes and provides a spectral and time-domain map of exciton-phonon assisted excitations. Using 12 fs long pulses, we resolve side-bands above the E ₂₂ transition that correspond with the RBM, G, G′, 2G and other multiphonon modes. The appearance of 2D-FT spectral cross-peaks explicitly resolves discrete phonon assisted population transfer that scatters excitations to the E ₂₂ (γ-pt) state, often through a second-order exciton-phonon coupling process. All 2D-FT peaks exhibit a strong peak amplitude modulation at the G-band period (21 fs) which we show originates from an impulsive stimulated Raman process that populates a ground-state G-band vibrational coherence over a 1.3 ps phonon lifetime.