Holographic D3-probe-D5 Model of a Double Layer Dirac Semimetal

TL;DR

This paper uses a holographic D3-probe-D5 model to explore inter-layer exciton condensation in a strongly coupled double monolayer Dirac semi-metal under magnetic fields, revealing conditions for condensate formation and phase behavior.

Contribution

It introduces a holographic model to analyze inter-layer exciton condensation, highlighting the effects of charge balance, layer separation, and symmetry breaking in strongly coupled systems.

Findings

Inter-layer condensates form at any layer separation when charges are balanced.

Charge neutrality leads to condensates only at small separations, with intra-layer condensates dominating at larger distances.

Spontaneous charge balance can occur via symmetry breaking in multi-species semi-metals.

Abstract

The possibility of inter-layer exciton condensation in a holographic D3-probe-D5 brane model of a strongly coupled double monolayer Dirac semi-metal in a magnetic field is studied in detail. It is found that, when the charge densities on the layers are exactly balanced so that, at weak coupling, the Fermi surfaces of electrons in one monolayer and holes in the other monolayer would be perfectly nested, inter-layer condensates can form for any separation of the layers. The case where both monolayers are charge neutral is special. There, the inter-layer condensate occurs only for small separations and is replaced by an intra-layer exciton condensate at larger separations. The phase diagram for charge balanced monolayers for a range layer separations and chemical potentials is found. We also show that, in semi-metals with multiple species of massless fermions, the balance of charges required for Fermi surface nesting can occur spontaneously by breaking some of the internal symmetry of the monolayers. This could have important consequences for experimental attempts to find inter-layer condensates.