Many experiments on unconventional superconductors consistently find a peculiar energy scale, distinct from the regular superconductivity gap. This second energy scale is called ’pseudo gap’, and its physical origin is still debated. Some theories relate the pseudo gap to a long-range order that competes with superconductivity. Recent X-ray experiments suggest that an incommensurate charge-density-waves (CDW) order is indeed present in the cuprate family of high-Tc superconductors.
By analyzing the Lindhard theory of scattering, we propose a different interpretation for these results. We claim that the experimental findings are simply due to Friedel oscillations, enhanced by the scattering of quasiparticles from nested segments of the Fermi surface. Starting from existing phenomenological models of the Fermi surface, we numerically evaluate the Lindhard function and compare our results to X-ray experiments. The similarity in the results and our ability to predict the position and the width of the X-ray peaks loses the connection between charge modulations and unconventional superconductivity.

The lecture is based on the paper we wrote, which is now on the arxiv here: http://arxiv.org/abs/1507.04345