  (Quasi-)one-dimensional systems exhibit various fascinating properties such
as Luttinger liquid behavior, Peierls transition, novel topological phases, and
the accommodation of unique quasiparticles (e.g., spinon, holon, and soliton,
etc.). Here we study molybdenum blue bronze A0.3MoO3 (A = K, Rb), a canonical
quasi-one-dimensional charge-density-wave material, using laser-based
angle-resolved photoemission spectroscopy. Our experiment suggests that the
normal phase of A0.3MoO3 is a prototypical Luttinger liquid, from which the
charge-density-wave emerges with decreasing temperature. Prominently, we
observe strong renormalizations of band dispersions, which is recognized as the
spectral function of Holstein polaron derived from band-selective
electron-phonon coupling in the system. We argue that the strong
electron-phonon coupling plays a dominant role in electronic properties and the
charge-density-wave transition in blue bronzes. Our results not only reconcile
the long-standing heavy debates on the electronic properties of blue bronzes
but also provide a rare platform to study novel composite quasiparticles in
Luttinger liquid materials.
