Chirality Induced Second Harmonic Generation in Aligned and Enantiomer Enriched Carbon Nanotubes

Aligned assemblies of single-chirality semiconducting carbon nanotubes (CNTs) are ideal materials for developing nanoelectronic, optoelectronic, and quantum photonic devices. Although left- and right-handed CNTs have identical properties in many aspects, enantiomer-dependent properties can manifest in magneto-transport, optical polarization selection, and nonlinear optics. For example, theoretical studies have predicted a large, resonance-enhanced second-order nonlinear optical susceptibility up to nm/V in perfect chiral CNT ensembles, but the value has never been experimentally verified due to mixed chirality components, poor alignment, and low densities. Here, we report the synthesis of centimeter-scale single-enantiomer, highly packed, and aligned (11,-5) CNT thin films using the controlled vacuum filtration method. We observed giant second harmonic generation (SHG) from the samples with effective second-order nonlinear optical susceptibility up to 70 pm/V, which corresponds to 350 pm/V for an enantiomerically pure, densely packed and perfectly aligned solid as predicted when the fundamental frequency resonates with the transition of the CNTs at 1000 nm. We confirmed that the SHG signal originates from the inversion symmetry breaking from the intrinsic chirality of the film, instead of surface defects, by angle and polarization dependent SHG measurements. Our findings provide a fast and scalable method for characterizing the alignment and enantiomer purity of CNT films, and establish them as an excellent material for nonlinear optical studies and applications.