Fig. 2: Doping dependence.

a temperature dependence of the resistivity and its derivative measured upon cooling in BaNi₂As₂, b of the integrated intensity of the q_I-CDW = (0.28,0,0) and q_C-CDW = (1/3,0,1/3) superstructure peaks (measured upon cooling) in BaNi₂As₂ (c) temperature dependence of the E_g,2 phonon intensity in BaNi₂As₂ (after background subtraction and Bose-factor correction, Supplementary Note 3) (d) temperature dependence of the E_g,1 phonon intensity in BaNi₂As₂ (after background subtraction and bose correction, Supplementary Note 3). e, f, g, h same as (a, b, c, d) for \({{{{{\rm{Ba}}}}}}{{{{{{\rm{Ni}}}}}}}_{2}{({{{{{{\rm{As}}}}}}}_{1-x}{{{{{{\rm{P}}}}}}}_{x})}_{2}\)(x = 3.5%) (i, j, k, l) same as (a, b, c, d) for \({{{{{\rm{Ba}}}}}}{{{{{{\rm{Ni}}}}}}}_{2}{({{{{{{\rm{As}}}}}}}_{1-x}{{{{{{\rm{P}}}}}}}_{x})}_{2}\)(x =7.6%) (m, n, o, p) same as (a, b, c, d) for \({{{{{\rm{Ba}}}}}}{{{{{{\rm{Ni}}}}}}}_{2}{({{{{{{\rm{As}}}}}}}_{1-x}{{{{{{\rm{P}}}}}}}_{x})}_{2}\)(x = 10%). In each panel we have indicated the position of the triclinic transition (upon cooling) T_Tri, of the local minimum of dR/dT T_rho and of the temperature at which the I-CDW intensity starts to grow T_I-CDW. The shaded area corresponds to the uncertainty on the determination of T^* at which the E_g phonon starts to broaden.