Charge density waves in NbSe sub(3): The models and the experimental evidence

Charge density wave (CDW) ordering in the prototypical low-dimensional compound NbSe sub(3) is reconsidered. It is shown that the model with two incommensurate modulations, [inline image] and [inline image], localized on type-III and type-I bi-capped trigonal prismatic columns, does not explain details, revealed by various microscopic methods. An alternative explanation, based on the existence of modulated layered nano-domains below both CDW onset temperatures, is suggested. It accounts for the presence of the [inline image] modulation in the STM images recorded above the [inline image] CDW transition and for the absence of [inline image] satellites in the corresponding diffraction patterns. The long periodic modulation, detected by LT STM, is attributed to a beating between the two CDWs, centered on adjacent columns of the same type. Such pairs of alternatively modulated columns represent the basic modulation units, ordered into nano-domains.