Intertube Excitonic Coupling in Nanotube Van der Waals Heterostructures

Strong intertube excitonic coupling is demonstrated in 1D van der Waals heterostructures by examining the ultrafast response of radial C/BN/MoS₂ core/shell/skin nanotubes to femtosecond infrared light pulses. Remarkably, infrared excitation of excitons in the semiconducting carbon nanotubes (CNTs) creates a prominent excitonic response in the visible range from the MoS₂ skin, even with infrared photons at energies well below the bandgap of MoS₂. Via classical analogies and a quantum model of the light–matter interaction these findings are assigned to intertube excitonic correlations. Dipole–dipole Coulomb interactions in the coherent regime produce intertube biexcitons, which persist for tens of femtoseconds, while on longer timescales (>100 ps) hole tunneling—from the CNT core, through the BN tunnel barrier, to the MoS₂ skin—creates intertube excitons. Charge transfer and dipole–dipole interactions thus play prominent roles on different timescales, and establish new possibilities for the multi-functional use of these new nanoscale coaxial cables.