Fig. 5. v_F of the light electrons, STEM-EELS of the CDW at 300 K, and CDW coherence lengths.

a The calculated $v_{\mathrm{F}}$ of the Te-p_x light electrons. Black ($v_{\mathrm{F}}$), calculated results using the temperature-dependent m* and n in Fig. 4b. Blue ($v_{\mathrm{F}}^{\mathrm{G}}$), calculations using Eq. (2) formulated for graphene. For clarity, all results normalized to the respective ones at 300 K. b, STEM-EELS elemental mapping of the CDW superlattice. Blue (yellow), Cu (Te). Solid (open) blue symbols, crystallographic Cu sites in the upper (lower) c portion of the 5a × 2c supercell. Solid (open) yellow symbols, Te in the upper (lower) part of the superlattice. c STEM-EELS probing of the Cu and Te core-level edges at each crystallographic site in (b) (related STEM-EELS spectra, Supplementary Fig. 12). Error bars, standard errors upon the analyses of the first derivative of the STEM-EELS spectra. Black horizontal lines, excitation edges of metallic Cu⁰ and Te⁰ acquired on thin metal-foil references. d The temperature-dependent coherence lengths of the CDW along c- (ξ_c, black) and a-axes (ξ_a, gray), respectively. Gray curve, the temperature dependence in accordance with the BCS theory. Error bars, standard deviations upon the averaging over five diffraction patterns.