Fig. 2: Experimental result.

a Transient transmissivity change dT/T induced by THz excitation in YFeO3 sample under various THz field strengths. b Fourier spectrum of a normalized to the peak at 0.3 THz. c Spectral amplitudes of 0.3 THz and 0.6 THz peaks as functions of incident THz field strength. Fitting curves with linear (0.3 THz) and quadratic (0.6 THz) dependence are also plotted.