Friedel Oscillations in Holographic Metals
  In this article we study the conditions under which holographic metallic states display Friedel oscillations. We focus on systems where the bulk charge density is not hidden behind a black hole horizon. Understanding holographic Friedel oscillations gives a clean way to characterize the boundary system, complementary to probe fermion calculations. We find that fermions in a "hard wall" AdS geometry unambiguously display Friedel oscillations. However, similar oscillations are washed out for electron stars, suggesting a smeared continuum of Fermi surfaces. 
V. G. M. Puletti, S. Nowling, L. Thorlacius, and T. Zingg
hep-th cond-mat.str-el