Coherent and incoherent transport in holographic models with spontaneously broken translations

 In holography it is relatively easy to construct the models which break translation symmetry either explicitly, or spontaneously, or both. AC transport in these models has a few interesting features, which were in focus for the past few years, including the gapped “pseudo-Goldstone” mode, the metal — Mott insulator transition, the residual incoherent conductivity and the contribution of the gapped coherent peak in DC conductivity due to “phase relaxation”. It is particularly interesting to study these features in detail, since they might have a direct representation in the experimental data on cuprates and doped Mott insulators. I will overview the subject and present several recent observations in models with either helical or periodic holographic lattices, which shed some light on the physics behind these interesting features.