Metal-insulator Transition by Holographic Charge Density Waves
  We construct a gravity dual for charge density waves (CDW) in which the translational symmetry along one spatial direction is spontaneously broken. Our linear perturbation calculation on the gravity side produces the frequency dependence of the optical conductivity, which exhibits the two familiar features of charge density waves, namely the pinned collective mode and gapped single-particle excitation. These two features indicate that our gravity dual also provides a new mechanism to implement the metal to insulator phase transition by CDW, which is further supported by the fact that d.c. conductivity decreases with the decreased temperature below the critical temperature. 
Yi Ling, Chao Niu, Jianpin Wu, Zhuoyu Xian, Hongbao Zhang
hep-th cond-mat.str-el gr-qc