Can bilayer graphene become a fractional metal?

TL;DR

This paper proposes that multi-band systems like doped AA bilayer graphene can host fractional metallic states, such as quarter-metals, where only a fraction of the Fermi surface is active, expanding the concept of half-metals.

Contribution

It introduces the concept of fractional metals in multi-band systems and demonstrates the possibility of quarter-metal states in doped AA bilayer graphene under specific interactions.

Findings

Doped AA bilayer graphene can host a quarter-metal state.

Fractional metals can emerge at higher doping levels.

Transport properties of these fractional metals are briefly analyzed.

Abstract

It is known that electron interactions can cause a perfect spin polarization of the Fermi surface of a metal. In such a situation only half of the non-interacting Fermi surface is available, and thus this phase is commonly referred to as a 'half-metal'. Here we argue that, in multi-band electronic systems with nesting, further 'fractionalization' of the Fermi surface is possible. Taking the AA bilayer graphene as a convenient test case, we demonstrate that, under suitable conditions imposed on the electron interactions, doped AA bilayer graphene can host a 'quarter-metal' state. In such a state, only one quarter of the non-interacting Fermi surface (Fermi contour) reaches the Fermi energy. At higher doping level, other 'fractional' metals can emerge. We briefly analyze the transport properties of these proposed phases.