Fig. 3: Temperature dependent evolution of the (2 × 2) CDW in Ba_0.23K_0.77Fe₂As₂.

a Temperature-dependent constant current differential conductance maps dI/dV_cc(r, V) at V = −10 mV reveals the progressive attenuation of the CDW, which becomes completely suppressed above 10 K [(V_s, I_s) = −10 mV, 200 pA; \({V}_{{{{{\rm{mod}}}}}}=0.75\,{{{{\rm{mV}}}}}\)]. All map slices were taken in the same surface location. b The associated Fourier transformations of a. Black circles mark the As- lattice peaks, red squares mark the charge order peaks. c Plot of the extracted intensities of the CDW peak as a function of temperature. All the peak intensities are normalised to that of the As- unit cell Bragg peak. The grey solid line shows the trend of the intensity drop. d Point dI/dV spectra taken from the As-terminated surface at two different temperatures: 300 mK and 12 K [(V_s, I_s) = − 10 mV, 200 pA; \({V}_{{{{{\rm{mod}}}}}}=0.25\,{{{{\rm{mV}}}}}\)]. The spectra are vertically offset for clarity. e Histogram of the spatial distribution of the CDW peak energies. Solid purple and green lines are the results from numerical fittings using a Gaussian function.