Exciton Condensation in a Holographic Double Monolayer Semimetal

TL;DR

This paper investigates exciton condensate phases in a double monolayer Weyl semi-metal using holographic duality, revealing complex phase transitions influenced by charge density, layer separation, and multiple fermion species.

Contribution

It introduces a holographic model for exciton condensation in Weyl semi-metals, uncovering new phase transitions and the role of charge balance in exciton formation.

Findings

Phase diagram with inter-layer and intra-layer condensates

Strong inter-layer condensation when charge densities are balanced

Spontaneous charge balance in systems with multiple fermion species

Abstract

The formation of intra-layer and inter-layer exciton condensates in a model of a double monolayer Weyl semi-metal is studied in the strong coupling limit using AdS/CFT duality. We find a rich phase diagram which includes phase transitions between inter-layer and intra-layer condensates as the charge densities and the separation of the layers are varied. The tendency to inter-layer condensation is strongest when the charge densities are balanced so that the weak coupling electron and hole Fermi surfaces would be nested. For systems with multiple species of massless Fermions, we find a novel phase transition where the charge balance for nesting occurs spontaneously.