Symmetry breaking in zero-field two-dimensional electron bilayers

TL;DR

This paper theoretically investigates spontaneous symmetry breaking in low-density 2D electron bilayers, revealing a transition to a pseudospin XY ferromagnetic phase driven by interlayer Coulomb interactions.

Contribution

It demonstrates a U(1) layer symmetry breaking transition using a self-consistent mean field approach, confirming earlier simpler models and identifying a new low-density phase.

Findings

Identification of a U(1) symmetry breaking transition at low densities

Validation of earlier Hartree-Fock results with a more rigorous method

Prediction of a pseudospin XY ferromagnetic phase in 2D bilayers

Abstract

We theoretically consider bilayers of two dimensional (2D) electron gases as in semiconductor quantum wells, and investigate possible spontaneous symmetry breaking transitions at low carrier densities driven by interlayer Coulomb interactions. We use a self-consistent technique implementing mean field truncations of the interacting four-fermion terms, and find a U(1) layer symmetry breaking transition at low carrier densities where the individual layer identities are lost leading to an effective pseudospin XY ferromagnet in the 2D plane. Our results validate earlier theoretical works using simpler restricted Hartree-Fock techniques, and establish the pseudospin XY ferromagnet as a possible low-density symmetry broken phase of 2D bilayers.