Structural study of the charge-density-wave phase transition of the blue bronze : K0.3MoO3

Abstract

We present an X-ray study of the Peierls transition of the blue bronze K0.3MoO3, including the temperature dependence of the intensity of the first order and second order satellite reflections below Tc, a complete characterization of the structural fluctuations above Tc (both their temperature dependence and their anisotropy) and an accurate determination of the wave vector of the charge density wave above and below Tc. An analysis of the phase transition within a mean field theory is justified and yields reasonable values of the electron phonon coupling and of the Coulomb interaction between charge density waves. The value of the modulation wave vector is explained as resulting from the presence of two conducting quasi one dimensional bands crossing the Fermi level E F and of a third one located about 650 K above E F. The opening of an absolute gap at the Fermi level occurs at the Peierls transition due to the folding of one conduction band on the other, and leads to a semiconducting state below Tc. Finally our measurements do not reveal any clear commensurate-incommensurate phase transition in temperature.