  We construct zero-temperature solutions of supergravity theories in five and
four dimensions which interpolate between two copies of anti-de Sitter space,
one of which preserves an abelian gauge symmetry while the other breaks it.
These domain wall solutions can be lifted to solutions of type IIB string
theory and eleven-dimensional supergravity. They describe quantum critical
behavior and emergent relativistic conformal symmetry in a superfluid or
superconducting state of a strongly coupled dual gauge theory. We include
computations of frequency-dependent conductivities which exhibit power law
scaling in the infrared, with exponents determined by irrelevant perturbations
to the symmetry-breaking anti-de Sitter background.
