Fig. 2. Experimental demonstration of photoinduced nonreciprocal circular dichroism in WS₂.

a, b show cases of σ⁺ and σ⁻ probes spectral reflectivity, under wavevector inversion geometry (for k = k_z and k = −k_z cases), for the σ⁻ pump incidence. Solid lines show the result of fitting by a modified Fresnel equation with surface conductivity described by a Lorentzian model (see Methods for details). Inset shows the optical microscope image of an encapsulated WS₂ monolayer on a glass substrate. c, d show pump power dependent dichroic response as seen in reflectivity from the sample (see Eq. 4) for probes coming from opposite directions. Here 600 nm σ⁻ pump is incident as in positive k_z direction (as shown in Fig. 1). The results for the σ⁺ pump can be found in the Supplementary Note 2.