Extended Data Fig. 7: QPI analysis of raw Fourier transforms.

(a, d) Raw Fourier transform (FT) of dI/dV maps in (a) Fig. 4a and (d) Extended Data Fig. 3a at 4.5 K. It is evident that rotation symmetry is broken even before two-fold symmetrizing the data. Black circles enclose the Bragg peaks, and blue circles enclose the 2a₀ CDW peaks. (b, e) FT linecut taken along the red dashed lines in (a,d) at different temperatures, normalized by subtracting the average FT background determined for each FT away from any prominent FT peaks. Red and blue arrows in the top panel point to the left and the right side of the q₂ scattering wave vector, which are almost the same height. (c,f) Amplitudes of the two sides of the q₂ wave vector (blue and red circles) corresponding to the peak heights denoted by red and blue arrows in (b, e) as a function of temperature. The amplitude suppression plotted in (c, f) is nearly identical to that presented in symmetrized data in Fig. 4. We use 0.36 Å⁻¹ average transverse to and 0.02 Å⁻¹ average along the linecut direction to create curves shown in (b); we use 0.29 Å⁻¹ average transverse to and 0.04 Å⁻¹ average along the linecut direction to create curves shown in (e). Error bars in (c, f) represent standard errors obtained by Lorentzian fits to data shown in (b, e). STM setup conditions: (a–c) V_sample = −6 mV, V_exc = 1 mV, I_set = 80 pA; (d, e) V_sample = −5 mV, V_exc = 1 mV, I_set = 50 pA.