Extended Data Fig. 4: THz field-induced circular and linear dichroism and temperature dependence.

a. THz-induced circular dichroism ΔCD measurements at 118K (green) and at 140K (grey). ΔCD is measured as a difference in transmittance of right-circularly polarized (RCP) and left-circularly polarized (LCP) probe beams. At high temperature (140K) ΔCD signal is absent, indicating there are no experimental artifacts in our setup that would result in ΔCD signal. b. Suppression of equilibrium linear dichroism by THz pulse at 118K. In equilibrium, transmission of horizontally polarized light is 2.3 times larger than the vertically polarized light, which reduces by ~1% after THz pumping, as shown in b. Since LD is proportional to the square of zigzag AFM order parameter, we can conclude that the THz pulse suppresses the AFM order by about  ~0.5%. c. Raw data of temperature dependent Δη experiments performed near Néel temperature with fine steps. It shows a marked change near transition point. A box with black dashed lines marks the region near transition a build-up of pre-time zero signal. Figure 2e in the Main Text is obtained by measuring the signal amplitude at long time delays (~170 ps). The pre-timezero signal decreases with temperature for T < 118K, whereas it increases with increasing temperature for higher temperatures.