We obtain holographic realizations for systems that have strong similarities
to Mott insulators and supersolids, after examining the ground states of
Einstein-Maxwell-scalar systems. The real part of the AC conductivity has a
hard gap and a discrete spectrum only. We add momentum dissipation to resolve
the delta function in the conductivity due to translational invariance. We
develop tools to directly calculate the Drude weight for a large class of
solutions and to support our claims. Numerical RG flows are also constructed to
verify that such saddle points are IR fixed points of asymptotically AdS_4
geometries.Comment: 52 pages, jheppub, 15 figures; v2: minor corrections, references
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