Edge Magnon Excitation in Spin Dimer Systems

TL;DR

This paper studies edge magnon modes in spin dimer systems on a bilayer honeycomb lattice, revealing how quantum phase transitions influence edge excitations and drawing parallels to graphene and monolayer honeycomb systems.

Contribution

It demonstrates the evolution of edge magnon modes across quantum phase transitions in bilayer honeycomb spin systems, highlighting the effects of magnetic ordering on edge excitations.

Findings

Flat edge magnon mode in disordered phase

Edge mode dispersion deviates from flat in ordered phase

Evolution of edge modes across quantum phase transition

Abstract

Magnetic excitation in a spin dimer system on a bilayer honeycomb lattice is investigated in the presence of a zigzag edge, where disordered and ordered phases can be controlled by a quantum phase transition. In analogy with the case of graphene with a zigzag edge, a flat edge magnon mode appears in the disordered phase. In an ordered phase, a finite magnetic moment generates a mean-field potential to the magnon. Since the potential is nonuniform on the edge and bulk sites, it affects the excitation, and the dispersion of the edge mode deviates from the flat shape. We investigate how the edge magnon mode evolves when the phase changes through the quantum phase transition and discuss the similarities to ordered spin systems on a monolayer honeycomb lattice.