Broken discrete symmetries in a frustrated honeycomb antiferromagnet

TL;DR

This study explores the complex magnetic phases and symmetry-breaking phenomena in a frustrated honeycomb antiferromagnet at zero and low temperatures using Monte Carlo simulations, revealing multiple broken discrete symmetries and magnetic structures.

Contribution

It provides the first detailed phase diagram of the $J_1$--$J_2$ honeycomb antiferromagnet at the strongly frustrated point, identifying novel symmetry-breaking phases and magnetic states.

Findings

Identification of three distinct field regimes with different broken symmetries.

Discovery of a 1/2-magnetization plateau with $Z_4$ symmetry breaking.

Observation of an intermediate phase breaking both $Z_3$ and $Z_4$ symmetries.

Abstract

We study the magnetic phase diagram of the $J_1$--$J_2$ Heisenberg antiferromagnet on a honeycomb lattice at the strongly frustrated point $J_2/J_1=1/2$ using large-scale Monte Carlo simulations. At low temperatures we find three different field regimes, each characterized by different broken discrete symmetries. In low magnetic fields up to $h_{c1}/J_1\approx 2.9$ the $Z_3$ rotational lattice symmetry is spontaneously broken while a 1/2-magnetization plateau is stabilized around $h_{c2}/J_1=4$. The collinear plateau state and the coplanar state in higher fields break the $Z_4$ translational symmetry and correspond to triple-$q$ magnetic structures. The intermediate phase $h_{c1}<h<h_{c2}$ has an interesting symmetry structure, breaking simultaneously the $Z_3$ and $Z_4$ symmetries. At much lower temperatures the spatial broken discrete symmetries coexist with the quasi long-range order of the transverse spin components.