Fig. S6.

(A) Low energy fits of the $B_{1g}$ response of sample MK at 2.33 eV ($532\hspace{0.17em}\mathrm{nm}$) using Eq. S5. (B) Temperature dependences of the inverse of the two contributions to the nematic susceptibility, $A_1$ and $A_2$ (red triangles; same as in Fig. 4). The dashed line is a linear fit of $A_1^{-1}$ between $T_{\text{S}}$ and $150\hspace{0.17em}\mathrm{K}$. It crosses the x axis at $T^{*}=11\hspace{0.17em}\mathrm{K}$. (C) Temperature dependence of the line width $\mathrm{\Gamma }$ of the QEP. The dashed line is a linear fit between $T_{\text{S}}$ and $150\hspace{0.17em}\mathrm{K}$. It crosses the x axis at $T^{\ast \ast }=66\hspace{0.17em}\mathrm{K}$.