Holographic conductivity of zero temperature superconductors

Using the recently found by G Horowitz and M Roberts (arXiv 0908 3677) numerical model of the ground state of holographic superconductors (at zero temperature), we calculate the conductivity km such models The universal relation connecting conductivity with the reflection coefficient was used for finding the conductivity by the WKB approach The dependence of the conductivity on the frequency and charge density is discussed Numerical calculations confirm the general arguments of (arXiv 0908 3677) in favor of non-zero conductivity even at zero temperature In addition to the Horowitz-Roberts solution we have found (probably infinite) set of extra solutions which are normalizable and reach the same correct RN-AdS asymptotic at spatial infinity These extra solutions (which correspond to larger values of the grand canonical potential) lead to effective potentials that also vanish at the horizon and thus correspond to a non-zero conductivity at zero temperature (C) 2010 Elsevier B V All rights reserved