Unbalanced Holographic Superconductors and Spintronics

TL;DR

This paper develops a holographic model for unbalanced s-wave superconductivity in 2+1 dimensions, exploring phase diagrams, transport properties, and potential string theory embeddings, with implications for spintronics.

Contribution

It introduces a minimal holographic framework for unbalanced superconductors, analyzing phase behavior, transport phenomena, and connections to string theory.

Findings

Phase diagram analysis reveals conditions for superconducting phases.

Holographic Mott's two-current model applied to spin and charge transport.

Discussion of possible inhomogeneous LOFF-like phases.

Abstract

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 AdS_4 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.