Effect of the electric depinning of an incommensurate CDW on the phonon spectrum probed by X-ray diffuse scattering experiments

The CDW state appears in the diffraction pattern as an incommensurate modulation of the lattice, the wavevector of the modulation is related to the Fermi wavevector of the condensed electrons, QIC~2kF. One of the goals of these proposals is to solve a long-standing fundamental controversy, that goes back to the early days, on the means by which the CDW state is created: either weak or strong electron-phonon coupling. A key point in this controversy is how the CDW is pinned to the lattice, and therefore experiments under an applied electric field are mandatory. IXS experiments are in principle feasible but are time consuming and, in view of our past experience, it is very unlikely that they can be of much help in this task [HC-4045]. An alternative approach that we would like to explore in this proposal is the study of the intensity of the diffuse scattering under an applied electric field through the threshold value and at different temperatures.