Fig. 3. Suppression of the CDW order via potassium doping.

a, The structural phase diagram of BKSO based on neutron (Supplementary Fig. 2) and X-ray (Supplementary Fig. 3) diffraction data. Black diamonds, tan crosses and red squares represent the face-centred cubic (fcc, Fm$\overline{3}$m), tetragonal (T, I4/mcm) and primitive cubic (C, Pm$\overline{3}$m) phases, respectively. The insets depict the local atomic structure of each phase, which shows transitions of the CDW order from the commensurate long range (Fm$\overline{3}$m) to short range (I4/mcm), and finally to complete suppression (Pm$\overline{3}$m). b, Raman spectra of BKSO measured with the excitation wavelength of 632 nm at 300 K. ω denotes the Raman shift in the unit of wavenumber. As highlighted in the dashed box, the breathing-mode phonon peak observed in the Fm$\overline{3}$m and I4/mcm phases disappears in the Pm$\overline{3}$m phase (x ≥ 0.65), confirming the CDW order is completely suppressed. The inset shows a schematic picture of the breathing-mode phonon.