Fig. 1. Lattices and electronic structures of the normal- and CDW-state CuTe.

a b-projected crystal structure in the normal state. Gray thick rectangle, unit cell. b STEM imaging of the CDW-modulated structure at 300 K. Gray thin rectangle, the CDW supercell of 5a × 2c with systematic Te displacements (∆x; picometer-level evaluations³⁸). The displacements organize into rows of trapezoids (gray) that show inverse Te-displacement directions in one trapezoid compared to the neighboring one in the same row, resulting in a wavelike displacement pattern of the periodicity of 5a. The Te displacements in the row right beneath (above) are anti-phase coupled, leading to the 2c periodicity. The gray sinusoidal waves, the wavelike, anti-phase coupled Te displacements. See text for the imperfection in the arrow-size repetition with the anticipated superperiodicity of 5a × 2c. c Electronic structure of the normal-state CuTe. Color, orbital decomposed Te-p states (black solid curves underneath, portraying the band dispersions). Black solid curves without color overlays, Cu 3d states. Fermi level, 0 eV. d Blowup of the CDW-state electronic structure along ΓX (i.e., the CDW counterpart to the light gray box in c). The CDW-gap opening at the Fermi level (black arrow) is dominated by one of the two practically linearly-dispersing Te-p_x bands. e Blowup of the CDW-state electronic structure around the dark gray-boxed region in c. f The high-symmetry directions in reciprocal space. g FS projected onto the X-Γ-Y plane at c* = 0. The Te-p_x bands (red) are sheet-like and in favor of FS nesting by q_N. The Te-p_y band (blue) forms a hole pocket.