Fig. 4: Third-order optical nonlinearity in tBLG electrically tuned by ion-gel-based top gating.
From: Enhanced third-harmonic generation by manipulating the twist angle of bilayer graphene
a Schematic diagram of the ion-gel-coated top-gating graphene device. b Microscope image of the graphene area corresponding to the white-coloured rectangle (highlighted with a white arrow) in (a). Inset: enlarged microscope image of a selected tBLG region consisting of various twist angles represented with different colour circles, whose Raman spectra are shown in Supplementary Fig. S4b. Measured THG images of the tBLG region (inset in b) at c Vg = 0 V and d Vg = –1.8 V, where the strongest THG occurs from grey-circled tBLG and green-circled tBLG, respectively. e THG intensities normalized by the THG intensity of MLG at Vg = 0 V for each graphene position before/after applying a Vg of –1.8 V. f Gating-induced THG enhancement factor; the rate of increased THG intensity at Vg = –1.8 V compared to the THG intensity at Vg = 0 V at each graphene position. The number indicates the sample location shown in the inset in (b)
