X-ray diffraction from pinned charge density waves

Abstract

Abstract. We present an x-ray study of doped charge density waves systems. When a 2k f -charge density wave is strongly pinned to impurities, an interference effect gives rise to an asymmetry between the intensities of the +2k f and −2k f satellite reflections. Moreover, profile asymmetry of the satellite reflections indicates the existence of Friedel oscillations (FOs) around the defects. We have studied these effects in V-and W-doped blue bronzes. A syncrotron radiation study of the V-doped blue bronze clearly reveals the presence of FO around the V atoms.

Study of Molecular Conductors by X-ray Diffuse Scattering

“…Nevertheless, it is now well-established that CDW long-range order is destroyed by impurities, as predicted by the above-mentioned theories. Indeed, diffraction experiments clearly show that introduction of disorder broadens the 2 k F satellite reflections, either in blue bronze, − NbSe 3 , − or in molecular conductors, as we shall see. Moreover, squared Lorentzian line shapes are usually observed, showing that the Lee-Rice domain image is relevant.…”

“…In a 3D system, the region in which the phase changes has to be as small as possible . Theoretical works then considered a structure with small and large scale variations. − Other authors , have stressed the importance of Friedel oscillations around impurities, and the importance of their phase shift …”

“…For a CDW, two terms dominate this equation: 184,185,197 (1) The bakscattering term at q ∼ (2k F is responsible for the pinning of the CDW phase on the impurity. In the FLR model, where the impurity potential is supposed to have the simple form v(rr m ) ) Uδ(rr m ), this term dominates eq 5.5.…”

Diffuse X-ray scattering studies of molecular conductors

“…Nevertheless, it is now well-established that CDW long-range order is destroyed by impurities as predicted by the above-mentioned theories. Indeed, diffraction experiments clearly show that introduction of disorder broaden the 2k F satellite reflections, either in blue bronze, 147,[157][158][159] NbSe 3 [160][161][162][163] or in molecular conductors, as we shall see. Moreover, squared Lorentzian line shapes are usually observed, 159 showing that the Lee-Rice domain image is relevant.…”

“…[142][143][144] Other authors 145,146 have stressed the importance of Friedel oscillations around impurities, and the importance of their phase shift. 147 Finally, let us mention that this problem of CDW pinning has been revisited recently, due to its similarity with vortices pinning in superconductors. 148,149 The ground state of the weak pinning case is described by a Bragg glass, [150][151][152][153] in which vortices positions (or the CDW phase) have a quasi-long range order (QLRO) for distances larger than the Lee-Rice domain sizes88.…”