  Using simple holographic models in $D=4$ spacetime dimensions we construct
black hole solutions dual to $d=3$ CFTs at finite charge density with a
Q-lattice deformation. At zero temperature we find new ground state solutions
with broken translation invariance, either in one or both spatial directions,
which exhibit insulating or metallic behaviour depending on the parameters of
the holographic theory. For low temperatures and small frequencies, the real
part of the optical conductivity has a power-law behaviour, with the exponent
determined by the ground state. We also obtain an expression for the the DC
conductivity at finite temperature in terms of horizon data of the black hole
solutions.
