Systematic Effective Field Theory Investigation of Spiral Phases in Hole-Doped Antiferromagnets on the Honeycomb Lattice

TL;DR

This paper uses effective field theory to explore spiral magnetic phases in hole-doped antiferromagnets on the honeycomb lattice, revealing unique symmetry properties and phase preferences relevant to high-temperature superconductor precursors.

Contribution

It introduces a systematic low-energy effective field theory approach to analyze magnetic phases in honeycomb lattice antiferromagnets, highlighting differences from square lattice systems.

Findings

Spiral phases can form due to a single-derivative term in the effective action.

The preferred phase depends on low-energy parameters, favoring either homogeneous or spiral states.

Spirals are not constrained to lattice directions due to an accidental continuous rotational symmetry.

Abstract

Motivated by possible applications to the antiferromagnetic precursor of the high-temperature superconductor Na$_x$CoO$_2\cdot$yH$_2$O, we use a systematic low-energy effective field theory for magnons and holes to study different phases of doped antiferromagnets on the honeycomb lattice. The effective action contains a leading single-derivative term, similar to the Shraiman-Siggia term in the square lattice case, which gives rise to spirals in the staggered magnetization. Depending on the values of the low-energy parameters, either a homogeneous phase with four or a spiral phase with two filled hole pockets is energetically favored. Unlike in the square lattice case, at leading order the effective action has an accidental continuous spatial rotation symmetry. Consequently, the spiral may point in any direction and is not necessarily aligned with a lattice direction.