Fig. 4: Simulated polarizability anisotropy of the aqueous salt solutions.

a, Total polarizability anisotropy ΔΠ of aqueous solutions of MgCl₂ at 1 M (blue), 2 M (green) and 4 M (red) concentrations. The amplitude increases linearly with concentration, as shown in the inset. b, ΔΠ of Na₂SO₄ solution at 1 M (red) exhibits modestly smaller amplitude relative to that of pure water (black). Red arrows in a and b indicate the increase and decrease of ΔΠ relative to pure water. \(E_{\rm{THz}}^2\), the square of the THz electric field. c,d, Single molecule ΔΠ^M (blue) and collision-induced ΔΠ^I (green) components of ΔΠ (red) for MgCl₂ solution at 4 M and for Na₂SO₄ at 1 M, respectively. Notably, while ΔΠ^I is the dominant contribution in the ΔΠ of the MgCl₂ solution, its contribution is minor in the Na₂SO₄ solution. The shadowed areas indicate standard errors.