Spin Waves and Dirac Magnons in a Honeycomb Lattice Zig-zag Antiferromagnet BaNi2(AsO4)2

TL;DR

This study investigates spin wave excitations in the honeycomb lattice antiferromagnet BaNi2(AsO4)2, revealing Dirac magnons and providing insights into magnetic interactions relevant for quantum spin liquid research.

Contribution

It reports the observation of symmetry-protected Dirac points in spin waves of BaNi2(AsO4)2, advancing understanding of magnetic excitations in honeycomb antiferromagnets.

Findings

Identification of Dirac points in spin wave spectrum

Determination of magnetic exchange interactions

Insight into zig-zag antiferromagnetic order

Abstract

The topological properties of massive and massless fermionic quasiparticles have been intensively investigated over the past decade in topological materials without magnetism. Recently, the bosonic analogs of such quasiparticles arising from spin waves have been reported in the two-dimensional (2D) honeycomb lattice ferromagnet/antiferromagnet and the 3D antiferromagnet. Here we use time-of-flight inelastic neutron scattering to study spin waves of the S = 1 honeycomb lattice antiferromagnet BaNi2(AsO4)2, which has a zig-zag antiferromagnetic (AF) ground state identical to that of the Kitaev quantum spin liquid candidate alpha-RuCl3. We determine the magnetic exchange interactions in the zig-zag AF ordered phase, and show that spin waves in BaNi2(AsO4)2 have symmetry-protected Dirac points inside the Brillouin zone boundary. These results provide a microscopic understanding of the zig-zag AF order and associated Dirac magnons in honeycomb lattice magnets, and are also important for establishing the magnetic interactions in Kitaev quantum spin liquid candidates.