Spectroscopic evidences of quantum critical charge fluctuations in   cuprates
  We calculate the optical conductivity in a clean system of quasiparticles coupled to charge-ordering collective modes. The absorption induced by these modes may produce an anomalous frequency and temperature dependence of low-energy optical absorption in some cuprates. However, the coupling with lattice degrees of freedom introduces a non-universal energy scale leading to scaling violation in low-temperature optical conductivity. 
M. Grilli, S. Caprara, C. Di Castro, and D. Suppa