Hidden multiferroic order in graphene zigzag ribbons

TL;DR

This paper reveals a hidden multiferroic order in graphene zigzag ribbons by describing their magnetic phase through a BCS wave function of spin-polarized electron-hole pairs, highlighting coupled magnetic and electric properties.

Contribution

It introduces a novel theoretical framework using a BCS wave function to describe multiferroic order in graphene ribbons without additional approximations.

Findings

Identification of spin-dependent dipoles in graphene ribbons

Demonstration of spin-resolved ferroelectricity

Explanation of zero total electric dipole and magnetization

Abstract

The insulating magnetic phase in graphene zigzag ribbons, predicted both by density functional and mean field Hubbard model calculations, is described without additional approximations with a BCS wave function of two phase-locked condensates of spin-polarized electron-hole pairs. The associated order parameter is the spin dipole operator that features both magnetic and electric order and accounts for the spin-resolved ferroelectricity of the system. Each condensate is associated to a spin-dependent dipole and their relative phase locking sets the total electric dipole and total magnetization equal to zero.