Fig. 4
Curie–Weiss fit to temperature dependence of Δd/d as a function of x for NaFe1−xNixAs. Temperature dependence of Δd/d and Curie–Weiss fit to the data for (a) x = 0.01, (b) x = 0.015, (c) x = 0.017, and (d) x = 0.017. Clear reduction below Tc is seen for all tetragonal samples. e Ni-doping dependence of Weiss temperature T*, showing a change of sign around x = 0.015, suggesting the presence of a nematic QCP. Data points in (a–d) with T < 50 K are obtained from the same neutron Larmor diffraction data used to extract δ in Fig. 3 (see Methods Section). All vertical error bars in the figure represent least-square fits to the raw data with errors of 1 s.d
