Giant nonlinear optical responses of carbyne

Carbyne, the third allotrope of carbon with alternating single and triple bonds, consists of sp-hybridized carbon atoms. Theoretically, with two degenerate pi-electron bands in one monomer, carbyne exhibits stronger nonlinear optical responses than graphene and it is acknowledged as a superior nonlinear optical material with just one p-electron band. Very recently, carbyne has been synthesized in the laboratory. Here, we demonstrate the giant nonlinear optical responses of carbyne. By employing the Z-scan technique using a femtosecond laser, we show that carbyne exhibits a large nonlinear absorption coefficient beta and a refractive index n(2) of 3.53 x 10(-13) m W-1 and -1.40 x 10(-13) esu at 800 nm excitation, respectively. Excellent broadband optical limiting responses of carbyne to femtosecond laser pulses at 800 and 400 nm were observed, respectively. We also establish that extensive p-electron delocalization and electron resonance enhancement of carbyne have made significant contributions to these nonlinear optical responses. These findings open the door to exploring the optical and technological applications of carbyne.