DFTT 32/2011 Unbalanced Holographic Superconductors

We present a minimal holographic model for s-wave superconductivity with unbalanced Fermi mixtures, in 2 + 1 dimensions at strong coupling. The breaking of a U(1)A “charge ” symmetry is driven by a non-trivial profile for a charged scalar field in a charged asymptotically AdS4 black hole. The chemical potential imbalance is implemented by turning on the temporal component of a U(1)B “spin ” field under which the scalar field is uncharged. We study the phase diagram of the model and comment on the eventual (non) occurrence of LOFF-like inhomogeneous superconducting phases. Moreover, we study “charge ” and “spin ” transport, implementing a holographic realization (and a generalization thereof to superconducting setups) of Mott’s two-current model which provides the theoretical basis of modern spintronics. Finally we comment on possible string or M-theory embeddings of our model and its higher dimensional generalizations, within consistent Kaluza-Klein truncations and brane-anti brane setups. 1 a