Abstract. We consider holographic superconductors whose bulk description consists of gravity minimally coupled to a Maxwell field and charged scalar field with general potential. We give an analytic argument that there is no ``hard gap'': the real part of the conductivity at low frequency remains nonzero (although typically exponentially small) even at zero temperature. We also numerically construct the gravitational dual of the ground state of some holographic superconductors. Depending on the charge and dimension of the condensate, the infrared theory can have emergent conformal or just Poincare symmetry. In all cases studied, the area of the horizon of the dual black hole goes to zero in the extremal limit, consistent with a nondegenerate ground state.

Key words: Spontaneous Symmetry Breaking; AdS-CFT Correspondence; Black Holes

E-print number: 0908.3677
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Received 3 September 2009, accepted for publication 8 October 2009
Published 5 November 2009