Fermionic spin excitations in two and three-dimensional antiferromagnets

TL;DR

This paper demonstrates that in frustrated two- and three-dimensional antiferromagnets, spin excitations can be fermionic spinons rather than bosonic magnons, revealing a new quantum state of matter.

Contribution

It shows that in the kagome antiferromagnet, spin excitations are spinons with fermionic statistics, contrasting with traditional magnon excitations in ordered magnets.

Findings

Spin excitations in kagome are spinons, not magnons.

Breaking a spinon pair costs 0.06 J in energy.

Ground state described as pairs of spinons with spin 0.

Abstract

Spin excitations in an ordered Heisenberg magnet are magnons--bosons with spin 1. That may change when frustration and quantum fluctuations suppress the order and restore the spin-rotation symmetry. We show that spin excitations in the $S=1/2$ Heisenberg antiferromagnet on kagome are spinons--fermions with spin 1/2. In the ground state the system can be described as a collection of small, heavy pairs of spinons with spin 0. A magnetic excitation of lowest energy amounts to breaking up a pair into two spinons at a cost of $0.06 J$.